Method and device for determining amount of carbon dioxide absorbed by soil permeate

Abstract

The present disclosure relates to devices, systems, uses and methods for determining the amount of carbon dioxide absorbed by a soil permeate (1). The method comprises positioning the device (3) at a measurement location (7) in the soil (2). A basicity storage layer (6) of the device (3) is arranged below the upstream wall (5), wherein the basicity storage layer (6) is formed from a material bearing a plurality of acidic groups on its surface. The method further comprises allowing the mineral (4) to react with water and carbon dioxide during the measurement time period to form a soil permeate (1) that permeates through the soil (2) and through the alkalinity storage layer (6), thereby deprotonating at least a portion of the acidic groups of the material forming the alkalinity storage layer (6). The method further comprises determining the total alkalinity absorbed by the alkalinity storage layer (6) and determining the total amount of carbon dioxide absorbed by the soil permeate (1) based on the determined total alkalinity absorbed by the alkalinity storage layer (6).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method of determining the amount of carbon dioxide absorbed by a soil infiltrate. BACKGROUND Measurement, reporting and verification (MRV) of carbon removal in field settings poses complex challenges due to its "open system" nature. Take enhanced weathering (EW) as an example, the complete system boundary would encompass the Earth's atmosphere, the project area (typically a plot of land using weathering material), and further river networks, CO2-transporting aquifers, groundwater, and ocean water. Considering the length and time scales of these different components, the project area and duration stand out as a spatiotemporal bottleneck, where the overall detection of the carbon dioxide removal (CDR) signal or related signals is most feasible. Currently, accurate quantification of the EW process remains a major challenge for scientists and project developers alike. Different approaches have been taken, focusing on the gas, liquid or solid phase (or combinations thereof) of the project area, all with their respective trade-offs.

[0003] Gas phase measurements aim at capturing the net CO2 flux from the atmosphere into the soil, which would give direct evidence of carbon removal. So far, these methods have been plagued by high uncertainties due to relatively large inflows and outflows from concurrent processes such as biological activity.

[0004] Soil-based approaches aim at tracking changes in the cation inventory of the solid phase. Alkali cation concentrations (e.g. Na, K, Mg, Ca) can subsequently be used to infer the production and flux of removed CO2. Highly precise cation concentrations can be determined, but the indirectness of this measurement reduces its utility in carbon removal MRV.

[0005] Solution phase methods can track the total amount of chemical species representing the ability to bind CO2 as bicarbonate and carbonate in the liquid phase, often referred to as total alkalinity (TA). Similar observations can be made based on dissolved inorganic carbon - the sum of dissolved CO2, carbonic acid, bicarbonate and carbonate - as bicarbonate typically represents the majority of the active component within TA. Currently, TA measurements are often made due to their practicality, but are typically performed on manually collected samples in a laboratory setting requiring skilled labor. Furthermore, while precise, accuracy issues still exist due to representativeness issues of the sample taken by, for example, a suction cup. It is a common approach to determine the concentration of TA in soil pore water in this way and subsequently use water balance to infer TA outflow from the field, however, this approach relies on several assumptions about the hydrological conditions of the study area. This method severely limits the applicability of TA measurements in large-scale, high-fidelity MRV work. As such, there is a need to provide a method that allows for reliable and accurate determination of the amount of captured carbon dioxide with high fidelity. SUMMARY It is therefore a general object of the present invention to advance the art with respect to quantifying the amount of captured carbon dioxide. In particular, it is an object of at least some variants to provide a method and device that allows for determination of the amount of carbon dioxide absorbed by soil infiltrate with high accuracy and fidelity. It is a further object of at least some variants to reduce the effort required to determine the amount of carbon dioxide absorbed by soil infiltrate, and optionally to reduce disturbance or intrusion into nature during the measurement process. For example, it is an object of at least some variants to provide a method and device that quantifies the amount of carbon dioxide captured in enhanced weathering processes.

[0007] The general object is achieved in a first aspect of the present disclosure by a method of determining the amount of carbon dioxide absorbed by soil infiltrate.

[0008] The method comprises a) positioning a device in a measurement location in soil such that an upstream wall of the device is arranged below the soil surface, preferably at least 10 mm below the soil surface. An alkalinity storage layer of the device is typically arranged below the upstream wall in a vertical direction, wherein the alkalinity storage layer is formed of a material carrying a plurality of acidic groups on its surface. In some variants, the alkalinity storage layer of the device is a buffer layer, for example a buffer layer having an initial pH of 3 to 7. In some variants, the positioned device is a device according to any of the embodiments described herein, in particular any of the embodiments described herein in the context of the third aspect of the present disclosure. The upstream wall can be referred to as a "top wall" in some variants.

[0009] The method further comprises b) allowing the solid (e.g. mineral matter) to react with water and carbon dioxide during the measurement period to form a soil permeate that permeates through the soil and through the alkalinity storage layer, thereby deprotonating at least a portion of the acidic groups of the material forming the alkalinity storage layer within the measurement period. In some variants, e.g. in variants in which the alkalinity storage layer is a buffer layer, in step b) the soil permeate permeating through the buffer layer can cause a change in the pH of the buffer layer within the measurement period.

[0010] The method further comprises c) determining the total alkalinity absorbed by the alkalinity storage layer within at least a portion of the measurement period.

[0011] The method further comprises d) determining the total amount of carbon dioxide absorbed by the soil permeate during the measurement period based on the determined total alkalinity absorbed by the alkalinity storage layer.

[0012] By providing an alkalinity storage layer whose acidic groups are at least partially deprotonated due to the soil permeate passing through the alkalinity storage layer, the method allows determining the amount of carbon dioxide absorbed by the soil permeate with high accuracy and with little interference with nature. In particular, the amount and nature of the chemical species formed by the reaction of carbon dioxide with water can be effectively stored in the device during the measurement period in the form of a change in the degree of deprotonation (respectively, degree of protonation) of the alkalinity storage layer. This is advantageous because the chemical species formed by carbon dioxide (including bicarbonate (HC03 - ), carbonate (C03 2- ) and hydroxide (OH - ), their respective salts) have limited stability, which means that directly measuring these species leads to inaccurate measurements. Furthermore, attempts to measure the cation inventory of the soil permeate rely on dubious and error-prone assumptions about the cation composition of the soil permeate and are therefore not an accurate proxy for determining the amount of captured carbon dioxide. In contrast, the method of the present disclosure effectively allows storing information about the amount of carbon dioxide absorbed by the soil permeate in the alkalinity storage layer in an accurate and stable manner.

[0013] For illustrative examples, an amount of carbon dioxide can react with water to form a soil infiltrate having a concentration of chemical species (e.g., bicarbonate and carbonate), and these chemical species can deprotonate acidic groups of the material forming the alkalinity storage layer upon contact with the acidic groups. If the alkalinity storage layer is a buffer layer, the soil infiltrate exiting the alkalinity storage layer can, for example, have substantially the same pH as the alkalinity storage layer. The degree of deprotonation of the alkalinity storage layer is indicative, first, of the amount of carbon dioxide absorbed by the soil infiltrate. Over time, the alkalinity storage layer can absorb total alkalinity, which is commensurate with the amount of carbon dioxide absorbed by the soil infiltrate. Thus, the total alkalinity absorbed by the alkalinity storage layer can be used to determine the total amount of carbon dioxide absorbed by the soil infiltrate. Optionally, the total amount of carbon dioxide absorbed by the soil infiltrate can be used to determine the amount of carbon dioxide captured in the enhanced weathering process. Furthermore, carbon dioxide removal can also be quantified in turn.

[0014] Depending on the application, different alkalinity storage layers can be used. For example, in some variations, the material forming the alkalinity storage layer is a material that changes its volume expansion upon infiltration of a soil infiltrate having a pH higher than 5, preferably upon infiltration of a soil infiltrate having a pH higher than 7, more preferably upon infiltration of a soil infiltrate having a pH of 8 or higher, more preferably 8 to 14. In some variations, the material forming the alkalinity storage layer is a material that changes its volume expansion upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions. For example, in some variations, the alkalinity storage layer can comprise a resin, preferably an ion exchange resin. The resin can, for example, be swellable and / or contractible upon contact with an aqueous solution having a pH higher than 7, preferably upon contact with an aqueous solution having a pH of 8 or higher. In some variations, the resin is swellable and / or contractible upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions (and respective salts of these ions, respectively). In some variations, the alkalinity storage layer is made of a material that is swellable and / or contractible upon contact with an aqueous solution having a pH higher than 7, preferably 8 or higher. In some variations, the alkalinity storage layer is made of a material that is swellable and / or contractible upon contact with an aqueous solution of bicarbonate ions and / or carbonate ions.

[0015] In several variations described herein, the material or resin forming the alkalinity storage layer is described as being swellable and / or contractible. In these variations, the material or resin forming the alkalinity storage layer is preferably swellable.

[0016] It will be appreciated that, generally, when a material is said to change its volume expansion (e.g. by swelling or shrinking) upon contact with a given substance (e.g. a soil infiltrate or an aqueous solution having a certain pH or containing certain species), at least in preferred variants, this means that the material exhibits a change in its volume expansion that is different from the possible change in volume expansion exhibited upon contact with water in the absence of the given substance. For example, in some variants, the alkalinity storage layer can be made of a material that is swellable and / or shrinkable (respectively changing its volume expansion) upon contact with water (e.g. due to the absorption of water). However, upon contact with water having a pH of 8 or more ((in some variants, a soil infiltrate containing aqueous bicarbonate and / or carbonate ions, respectively), the material can swell (respectively change its volume expansion) more strongly than it would otherwise swell upon contact with the same amount of water having a neutral pH (e.g. water not containing aqueous bicarbonate and carbonate ions). Thus, in some variants, the material forming the alkalinity storage layer is a material that changes its volume expansion upon infiltration of a soil infiltrate having a pH higher than 7 (preferably a pH of 8 or more) through the alkalinity storage layer, wherein the change in volume expansion is at least partially due to alkaline species in the soil infiltrate (e.g. due to species in the soil infiltrate causing a pH higher than 7, preferably a pH of 8 or more). In some variants, the material forming the alkalinity storage layer is a material that changes its volume expansion upon infiltration of a soil infiltrate containing aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer, wherein the change in volume expansion is at least partially due to the aqueous bicarbonate ions and / or aqueous carbonate ions contained in the soil infiltrate. In particular, the change in volume expansion can be due, for example, to a chemical reaction of the acidic groups with the aqueous bicarbonate ions and / or aqueous carbonate ions contained in the soil infiltrate. In some variants, the alkalinity storage layer comprises a resin that is swellable and / or shrinkable upon contact with an aqueous solution having a pH higher than 7 (preferably upon contact with an aqueous solution having a pH of 8 or more), wherein the swelling or shrinking is at least partially due to alkaline species in the soil infiltrate (e.g. due to species in the soil infiltrate causing a pH higher than 7, preferably a pH of 8 or more). In some variants, the alkalinity storage layer comprises a resin that is swellable and / or shrinkable upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions, wherein the swelling or shrinking is at least partially due to the aqueous bicarbonate ions and / or aqueous carbonate ions contained in the soil infiltrate.

[0017] In some variants, the alkalinity storage layer contacts a first side of a detection wall, such that a change in the volume expansion of the material forming the alkalinity storage layer results in a strain on the detection wall and / or a physical deformation of the detection wall. The detection wall may, for example, be elastically deformable, preferably by an elastic outward bulging of the detection wall on a second side of the detection wall opposite the first side of the detection wall, such that a change in the volume expansion of the material forming the alkalinity storage layer results in a physical deformation of the detection wall. In these variants, the penetration of the soil infiltrate through the alkalinity storage layer may, for example, result in a change in the volume expansion of the material forming the alkalinity storage layer, which can eventually be used to infer the amount of absorbed carbon dioxide. In some variants, the detection wall is at least partially arranged inside the housing. In particular, at least the first side of the detection wall can in some variants be arranged inside the housing. In some variants, the second side of the detection wall faces away from the alkalinity storage layer.

[0018] In some variants, the step of determining the total alkalinity absorbed by the alkalinity storage layer comprises determining, preferably measuring, a change in the volume expansion of the material forming the alkalinity storage layer over at least a portion of the measurement time period. In some variants, the step c) of determining the total alkalinity absorbed by the alkalinity storage layer (6) over at least a portion of the measurement time period comprises c.i) determining, e.g. measuring, a change in the volume expansion of the material forming the alkalinity storage layer over at least a portion of the measurement time period; and c.ii) determining the total alkalinity absorbed by the alkalinity storage layer over at least a portion of the measurement time period based on the change in the volume expansion of the material forming the alkalinity storage layer measured over at least a portion of the measurement time period. In some variants, the change in the volume expansion of the material forming the alkalinity storage layer is a swelling and / or shrinking of the material forming the alkalinity storage layer upon the penetration of the soil infiltrate formed by the reaction of the solid with water and carbon dioxide through the alkalinity storage layer. In some variants, the change in the volume expansion of the material forming the alkalinity storage layer is a swelling and / or shrinking of the material forming the alkalinity storage layer upon the penetration of the soil infiltrate containing aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer.

[0019] In some variants, the alkalinity storage layer is formed by a material carrying a plurality of acidic groups and a plurality of basic groups on its surface. For example, the material can comprise carboxylic acid groups and carboxylate groups.

[0020] In some variants, the alkalinity storage layer is arranged inside the housing.

[0021] In some variants, the solid comprises or consists of a mineral. For example, the solid can be a mineral. The solid is allowed to react with water and carbon dioxide during the measurement period to form a soil infiltrate, which infiltrates into the soil and through the alkalinity storage layer. Thereby, the solid is typically configured to undergo a chemical reaction with carbon dioxide and water to form a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions. The solid, preferably a mineral, is typically arranged on or in the soil. Thereby, when the solid, preferably a mineral, is allowed to react with water and carbon dioxide, the formed soil infiltrate infiltrates into the soil and through the alkalinity storage layer. In some variants, the solid, preferably a mineral, is arranged on the soil surface and / or in the surface soil layer. For example, the solid, preferably a mineral, can be arranged on the soil surface and / or within 300 mm, preferably within 80 mm, more preferably within 30 mm, even more preferably within 10 mm of the soil surface. It will be appreciated that the solid, preferably a mineral, is typically arranged between the soil surface and the upstream wall of the device. Depending on the application, the solid, preferably a mineral, can also be arranged at an elevated position, wherein the soil infiltrate drips from the elevated position onto the soil surface and further infiltrates into the soil. Typically, the solid, preferably a mineral, is arranged such that they are in direct contact with the ambient air. This allows for capturing carbon dioxide from the air. Alternatively or in combination, the solid, preferably a mineral, can be arranged in contact with soil pore gas. One potential advantage of doing so is that soil pore gas can contain a significantly higher concentration of carbon dioxide due to the respiration processes occurring within the soil. The solid, preferably a mineral, can also be exposed to carbon dioxide by, for example, using an additional carbon dioxide gas stream, which can optionally be arranged underground. Depending on the application, the solid, preferably a mineral, can be provided, for example, on flat soil or on ploughed soil.

[0022] In some variants, the method further comprises controlling the internal flux of soil penetrant penetrating through said device during the measurement period such that the internal flux has a known or determinable flux ratio with respect to the external flux of soil penetrant penetrating through a first reference segment of soil arranged outside said device. For example, in some variants, the internal flux of soil penetrant penetrating through said device is controlled such that the internal flux substantially maintains a predetermined flux ratio with respect to the external flux of soil penetrant penetrating through a first reference segment of soil arranged outside said device. The predetermined flux ratio can for example fall within a ratio of 1 :5 to 5:1, preferably 1 :2.5 to 2.5:1. In some variants, the method further comprises controlling the internal flux of soil penetrant penetrating through said device during the measurement period such that the internal flux substantially corresponds to the external flux of soil penetrant penetrating through a first reference segment of soil arranged outside said device. In this context, substantially corresponds means that the internal flux is within 25%, preferably within 15%, more preferably within 5% of the external flux. In some variants, the step of controlling the internal flux comprises controlling the vacuum pressure inside said device. As an example, when the internal flux is lower than the external flux, a negative pressure can be applied inside said device in order to draw in more soil penetrant. Conversely, if the internal flux is higher than the external flux, for example, an overpressure can be applied inside said device in order to draw in less soil penetrant. Controlling the internal flux to substantially correspond to the external flux allows measuring an amount of captured carbon dioxide representative of the whole study field, as compared to a small portion of the field where said device can be positioned. The first reference segment of soil can for example be arranged adjacent to said device in a horizontal direction orthogonal to the vertical direction. The first reference segment can be directly adjacent to said device, or it can be spaced apart from said device. In some variants, the first reference segment of soil is arranged adjacent to said device in a horizontal direction orthogonal to the vertical direction.

[0023] Depending on the application, different solids can be used. Since the solid, which can be for example a mineral, is mainly used to react with water and carbon dioxide to form a soil infiltrate that penetrates through the soil, it is understood that the solid can be a mineral, but is not limited to a mineral. Rather, generally a solid can be used. The solid is capable of reacting with water and carbon dioxide, typically forming bicarbonate and / or carbonate. This reaction typically occurs spontaneously at room temperature and 1 bar. This reaction is sufficient to equilibrate with gaseous carbon dioxide. While complete or quantitative conversion of carbon dioxide can be desirable, it is not necessarily required for the purpose of the present disclosure. The solid typically has a pH of 7 or higher, preferably 7 to 12. The solid can for example comprise one or more of the following: an industrial by-product, such as steel slag, cement kiln dust, fly ash, a concrete or a solid derived from concrete, such as recycled concrete aggregate, concrete particles or particles derived from concrete (where each concrete or particle derived from concrete can for example have a particle size of less than 1 cm 3 ).

[0024] Depending on the application, the solid preferably comprises or consists of a mineral. For example, in some variants, the solid comprises at least 50 wt.%, preferably at least 75 wt.%, more preferably at least 90 wt.% of a mineral. The mineral can but need not be crystalline. Typically, the mineral is an alkaline mineral. For example, an aqueous solution (100 g / L) or, if the mineral is poorly soluble, an aqueous suspension (100 g / L) of the mineral can preferably have a pH of 7 or higher, preferably 7 to 12, at room temperature. In some variants, the mineral comprises one or more of the following: an alkali metal oxide, an alkaline earth metal oxide, a silicate-containing mineral. In some variants, the mineral is selected from the list consisting of an alkali metal oxide, an alkaline earth metal oxide and a silicate-containing mineral. In some variants, the mineral comprises or consists of a silicate-containing mineral. For example, in some variants, the mineral comprises basalt and / or wollastonite.

[0025] The soil infiltrate penetrates through the soil and through the alkalinity storage layer. Thus, the soil infiltrate is typically water that penetrates into the soil on or above the soil surface. The soil infiltrate typically includes all water-based solutions, suspensions and dispersions that penetrate through the soil. In some variants, the soil infiltrate can be soil leachate.

[0026] Water and carbon dioxide are allowed to react with the solid, preferably a mineral, to form a soil infiltrate that penetrates through the soil during the measurement period. Due to this reaction, the soil infiltrate comprises chemical species formed by this chemical reaction. The chemical species typically include bicarbonate (HC03 - ), carbonate (C03 2- ) and hydroxide (OH -), the corresponding salts of these anions. Thereby, it can be said that a soil infiltrate with additional alkalinity is formed (i.e. an "additional alkalinity" compared to a soil infiltrate formed without contact to solids, preferably minerals). Depending on the nature of the chemical species and the concentration of the chemical species in the soil infiltrate, the soil infiltrate has a certain total alkalinity. The total alkalinity of a soil infiltrate is defined as the ability of the soil infiltrate to neutralize acids. In some variants, the total alkalinity TA(I) of the soil infiltrate can be provided as TA = [HCO3 - ] + 2[CO3 2- ]+ [B(OH)4 - ] + [OH - ] + [HPO4 2- ] + 2[PO4 3- ] + [SiO(OH)3 - ] + [HS - ] + 2[S 2- ] +[NH3] - [HSO4 + ] + - [HSO4 + ] - [HF]- [H3PO4] -[H + ] wherein [xyz] denotes the concentration of the respective species xyz. In particular, [SiO(OH)3 - ] refers at least in some embodiments to the concentration of orthosilicic acid and its derivatives (e.g. formed by condensation and / or deprotonation of orthosilicic acid). at least in some embodiments refers to the concentration of acetic acid and all other organic carboxylic acids. It is to be understood that among all chemical species contributing to the total alkalinity, some chemical species are more strongly related to the reaction of carbon dioxide and water than others. In particular, when carbon dioxide is allowed to react with water in the presence of solids, e.g. minerals such as oxides, the bicarbonate, carbonate and hydroxide ion concentrations can be more strongly affected than the concentration of some other species. Furthermore, when the total alkalinity is measured at different points in time, some chemical species can be essentially constant and can cancel out when comparing two or more total alkalinity measurements.

[0027] In some variants, the total alkalinity TA(I) of the soil infiltrate can be provided as TA(I) = [HCO3 – ] + 2×[CO3 2– ] + [OH – ] wherein [HCO3 - ] denotes the concentration of bicarbonate ions in the soil infiltrate, [CO3 2–[CO32] represents the concentration of carbonate ions in the soil permeate, and [OH – [OH ] represents the concentration of hydroxide ions in the soil permeate, typically at 25 °C and 1 bar. In a further approximation, the total alkalinity can be approximated as consisting of the bicarbonate ion concentration and the carbonate ion concentration.

[0028] The chemical species formed from the reaction of water and carbon dioxide in the presence of the solid, preferably mineral, is typically basic. Thus, the soil permeate formed can be described as having an additional alkalinity. The term "additional alkalinity" can describe the excess alkalinity of the soil permeate formed in the presence of the solid, preferably mineral, compared to the soil permeate formed in the absence of the solid, preferably mineral.

[0029] When the soil permeate permeates through the alkalinity storage layer, this typically changes the protonation / deprotonation profile of the acidic groups of the material forming the alkalinity storage layer. For example, in variants in which the alkalinity storage layer is a buffer layer, the permeation of the soil permeate causes a change in the pH of the buffer layer over the measurement period. Typically, deprotonation occurs, i.e. the pH of the buffer layer, for example, increases due to the permeation of the soil permeate through the buffer layer. For example, an overall increase in the pH can be observed over the measurement period. Depending on the application, the pH can increase steadily, or the pH can fluctuate over time, for example due to intermittent acidic parts of the soil permeate.

[0030] The total alkalinity of the soil permeate is absorbed by the alkalinity storage layer over the measurement period. In some variants in which the alkalinity storage layer is a buffer layer, the total alkalinity absorbed by the buffer layer over the measurement period corresponds to the change in the pH of the buffer layer over the measurement period. The total alkalinity absorbed by the buffer layer over the measurement period can be defined, for example, as the ability of the buffer layer to neutralize acids after the measurement period until the initial pH of the buffer layer is restored. As understood by the skilled person, the acids used for neutralization typically have a lower pH than the initial pH of the buffer layer. In some variants, the total alkalinity absorbed by the buffer layer over the measurement period can be defined as an excess molar amount of basic buffer group equivalents, wherein the excess basic buffer group equivalents correspond to the difference between the amount of basic buffer group equivalents after the measurement period and the amount of basic buffer group equivalents before the measurement period, i.e. at the initial pH. Thereby, the total alkalinity absorbed by the buffer layer over the measurement period can be defined as the molar amount of basic buffer group equivalents formed during the measurement period.

[0031] The term "amount of basic buffer groups equivalent" as used herein can in some variants be defined as the amount of basic buffer groups multiplied by n(eq), wherein n(eq) is the number of protons less of the basic buffer groups compared to the number of protons of the corresponding acidic buffer groups. For a buffer comprising only monoprotic acids, such as carboxylic acids, n(eq) is 1. In contrast, if the acidic buffer groups can be deprotonated twice, n(eq) is 2 for diprotonated basic buffer groups and 1 for monoprotonated basic buffer groups.

[0032] In some variants, such as when a carboxylate-carboxylic acid buffer is used, the total alkalinity absorbed by the buffer layer within the measurement time period can in some variants be defined as the molar amount of carboxylate groups formed during the measurement time period by deprotonation of the carboxylic acid groups. Thereby, the total alkalinity TA(absorbed) absorbed by the buffer layer within the measurement time period can in this variant be defined as: TA(absorbed) = n(carboxylate groups) T - n(carboxylate groups) 0 wherein n(carboxylate groups) T is the molar amount of carboxylate groups present after the measurement time period, and n(carboxylate groups) 0 is the molar amount of carboxylate groups present before the measurement time period, i.e. at the initial pH.

[0033] Typically, the total alkalinity of the soil permeate is at least partially, preferably completely, absorbed by the alkalinity storage layer. Completely can for example mean that more than 80%, such as more than 90%, preferably more than 95%, more preferably more than 99% of the total alkalinity of the soil permeate can be absorbed by the alkalinity storage layer before contacting the alkalinity storage layer. In some variants, the soil permeate leaving the alkalinity storage layer, such as the buffer layer, has the same pH as the alkalinity storage layer, such as the buffer layer. Additionally or alternatively, the soil permeate leaving the alkalinity storage layer can have a pH of 4 to 7, preferably 4 to 6, such as 4.5 to 5.5.

[0034] In some variants, the total alkalinity TA(absorbed) of the soil permeate absorbed within the measurement time period can be provided by: TA(absorbed) = TA(I) x Q(LW) x T wherein TA(I) is the total alkalinity of the soil permeate (typically as a concentration, such as in mol / L), Q(LW) is the average flow rate of the soil permeate permeating through the buffer layer, and T is the duration of the measurement time period.

[0035] The total alkalinity absorbed by the alkalinity storage layer can be determined in different ways. For example, in some variants, the step of determining the total alkalinity absorbed by the alkalinity storage layer over the measurement period comprises determining the total interval alkalinity absorbed by the alkalinity storage layer during a plurality of intervals over the measurement period; and determining the total alkalinity absorbed by the alkalinity storage layer over the measurement period based on the total interval alkalinity determined for the plurality of intervals. The total interval alkalinity can be determined, for example, by measuring the volume expansion (e.g. swelling and / or shrinking) of the alkalinity storage layer that occurs over the respective interval. Alternatively or in combination, for example in variants in which the alkalinity storage layer comprises or consists of a buffer layer, the total interval alkalinity can be determined, for example, by measuring the pH difference of the buffer layer that occurs over the respective interval (i.e. the pH of the buffer layer at the end of the respective interval minus the pH of the buffer layer at the beginning of the respective interval). In some variants, the pH differences obtained for all intervals can be summed to provide the total alkalinity absorbed by the buffer layer during the measurement period.

[0036] It can also be distinguished whether the total interval alkalinity value is positive or negative. As an example, it can be possible that the soil permeate can be mostly alkaline, but can include sporadic acidic intervals during which the soil permeate can be slightly acidic. If the acidity during these sporadic acidic intervals exceeds the acidity of the buffer layer (i.e. if the pH of the soil permeate is less than the pH of the buffer layer), this can distort the measurement results, as it can intermittently cause protonation of the buffer layer instead of deprotonation. This can potentially lead to inaccurate prediction of the amount of carbon dioxide captured. To address this challenge, the total interval alkalinity can be examined, and only positive total interval alkalinity values can be considered. In some variants, the step of determining the total alkalinity absorbed by the buffer layer over the measurement period is provided by summing the total interval alkalinity of all intervals for which a positive total interval alkalinity is determined. Optionally, the total interval alkalinity of all intervals for which a negative total interval alkalinity is determined is discarded. As used in the present context, a positive interval alkalinity means that the pH of the buffer layer increases (i.e. the buffer layer becomes more alkaline) over the respective interval. In contrast, as used in the present context, a negative interval alkalinity means that the pH of the buffer layer decreases (i.e. the buffer layer becomes more acidic) over the respective interval.

[0037] In some variants, the measurement period comprises at least three, preferably at least five, more preferably 10 to 1’000 intervals. The total interval alkalinity can be determined for each of these intervals, or for a selection of intervals, such as at least 30% of the intervals. In some variants, the total interval alkalinity is determined for a plurality of intervals of at least ten during the measurement period. Depending on the application, the intervals can have different durations. For example, in some variants, each interval can last for at least 10 minutes, preferably 1 hour to 10 days.

[0038] When measuring the total alkalinity absorbed by the alkalinity storage layer, the entire alkalinity storage layer can be subjected to the measurement, or only a part of the alkalinity storage layer (e.g. sub-layers and / or sub-sections) can be subjected to the measurement. For example, in some variants, the step of determining the total alkalinity absorbed by the alkalinity storage layer during the measurement period comprises determining the total alkalinity absorbed by at least a part of a plurality of sub-layers arranged on top of each other in a vertical direction; and subsequently, based on the determined total alkalinity absorbed by the respective sub-layers, determining the total alkalinity absorbed by the alkalinity storage layer during the measurement period. It is to be understood that the sub-layers are sub-layers of the alkalinity storage layer. In other words, the alkalinity storage layer comprises a plurality of sub-layers. In some variants, the total alkalinity can be determined for at least 10% of all sub-layers, preferably for at least 30% of all sub-layers. Depending on the application, the buffer layer can comprise at least three, such as at least five sub-layers.

[0039] Depending on the application (e.g. in variants in which the alkalinity storage layer comprises or consists of a buffer layer), the pH profile over the thickness of the buffer layer can be uniform, or it can fluctuate or deviate over the thickness. In some variants, the pH decreases from a top sub-layer to a bottom sub-layer, wherein the top sub-layer is arranged closest to the upstream wall in the vertical direction and the bottom sub-layer is arranged closest to the bottom wall in the vertical direction. The pH can for example decrease steadily, i.e. it can decrease from each sub-layer to each subsequent sub-layer (i.e. a sub-layer that is subsequent in the vertical direction), or it can increase intermittently, but show an overall decrease from the top sub-layer to the bottom sub-layer. When the pH does not decrease steadily, this can in some variants be indicative of an undesired backflow, which can render the measurement inaccurate.

[0040] In some variants, the total alkalinity absorbed by the alkalinity storage layer is provided as the sum of the total alkalinity absorbed by all sub-layers, if the determined total alkalinity absorbed by the respective sub-layers decreases from each sub-layer to each downstream sub-layer (i.e. a sub-layer that is subsequent in the vertical direction, e.g.).

[0041] Furthermore, in those variants, if the total alkalinity of at least one sublayer is lower than the total alkalinity of a downstream sublayer arranged directly underneath said at least one sublayer in the vertical direction, the total alkalinity of said at least one sublayer (i.e. of the at least one sublayer having the lower total alkalinity) is not included in the determination of the total alkalinity absorbed by the alkalinity storage layer. In some variants, only part of the total alkalinity of said at least one sublayer is included, e.g. with a correction factor. In some variants, if the total alkalinity of at least one sublayer is lower than the total alkalinity of a downstream sublayer arranged directly underneath said at least one sublayer in the vertical direction, the total alkalinity absorbed by the alkalinity storage layer is provided as the sum of the total alkalinity absorbed by the sublayers upstream and / or downstream of said at least one sublayer having the lower total alkalinity. In some variants, if the total alkalinity of an intermediate sublayer is lower than the total alkalinity of a downstream sublayer (i.e. e.g. a subsequent sublayer in the vertical direction) arranged directly underneath the intermediate sublayer in the vertical direction, the total alkalinity absorbed by the alkalinity storage layer is provided as the sum of the total alkalinity absorbed by the intermediate sublayer and all sublayers arranged upstream of the intermediate sublayer (i.e. e.g. above the intermediate sublayer in the vertical direction). The total alkalinity absorbed by the sublayers arranged downstream of the intermediate sublayer (i.e. e.g. below the intermediate sublayer in the vertical direction) is optionally discarded. In some variants, "lower than the total alkalinity of a subsequent sublayer arranged directly downstream of the intermediate sublayer in the vertical direction" means that the pH of the subsequent sublayer is at least 1%, preferably at least 3%, more preferably at least 10% higher than the pH of the intermediate sublayer. The variants described in this paragraph can relate to determining the total alkalinity absorbed by the alkalinity storage layer over a measurement period and / or over one or more intervals within a measurement period.

[0042] The total alkalinity absorbed by the buffer layer (respectively by the sublayer) can be determined in different ways. Since the total alkalinity absorbed by the buffer layer (respectively by the sublayer) usually corresponds to an increase of the pH of the buffer (respectively of the sublayer), a pH measurement can be used to determine the total alkalinity absorbed by the buffer layer (respectively by the sublayer). Thereby, in some variants, the step of determining the total alkalinity absorbed by the buffer layer during the measurement period comprises measuring the variation of the pH of the buffer layer during the measurement period. In some variants, the total alkalinity absorbed by the buffer layer (respectively by the sublayer) is determined by measuring the difference of the pH of the buffer layer (respectively of the sublayer) between two time points, for example the end point marking the end of the measurement period and the start point marking the beginning of the measurement period. The pH difference can also be determined for several intervals within the measurement period. In this case, for example, the pH differences can be summed to provide the overall variation of the pH. Optionally, intervals showing a negative pH difference, i.e. intervals with a net acidification, can be discarded and not included in said sum, which allows a more accurate determination of the total alkalinity absorbed during the measurement period. Based on the pH difference of the measurement period, for example, the total amount of alkalinity or of alkaline equivalents absorbed can be calculated, for example by taking into account the overall volume of the buffer.

[0043] In some variants, the total alkalinity absorbed by the buffer layer (respectively by the sublayer) can be determined by titration, for example by titrating at least a portion of the buffer layer (respectively of the sublayer) to a target pH. In some variants, the step of determining the total alkalinity absorbed by the buffer layer during the measurement period comprises titrating at least a portion of the buffer layer at the end of the measurement period to a target pH. Typically, the difference between the target pH and the initial pH is at least 0.4, preferably at least 1, more preferably at least 2. Additionally or alternatively, the target pH can be from 6.5 to 9.5, preferably from 7 to 9.

[0044] As an illustrative example, the total alkalinity absorbed by the buffer layer during the measurement period can be determined, for example, as follows: - at least a portion of the buffer layer can be titrated to a target pH at the beginning of the measurement period (i.e. in the initial state, i.e. before the absorption of the total alkalinity) to provide a first measurement value; - at least a portion of the buffer layer can be titrated to the target pH at the end of the measurement period (i.e. after the absorption of the total alkalinity) to provide a second measurement value; - the difference between the first measurement value and the second measurement value can provide the total alkalinity absorbed by the buffer layer during the measurement period.

[0045] Determining the total alkalinity absorbed by the buffer layer typically involves detection of a signal, and different signal detection can be envisaged. For example, signal detection can be achieved by on-demand addition of a pH-responsive indicator dye. Additionally or alternatively, signal detection can be performed spectroscopically, for example by measurement of visible light absorption, infrared absorption or by Raman signals, either directly on the relevant species or via addition of dye molecules. Additionally or alternatively, signal detection can be performed electrochemically by measuring the electrode potential difference between the sample solution and a reference. For example, an ISFET-based detector can be used.

[0046] As outlined herein, determining the total alkalinity absorbed by the buffer can involve titration. Titration can for example be performed by an acid provided by a pre-loaded compartment within the device. Additionally or alternatively, titration can be performed by in situ generation of H + Anodes pulses without the need for additional chemicals. Additionally or alternatively, titration and detection can occur in a thin layer sandwiched between a proton pump and a detector. Additionally or alternatively, plasmonic surfaces can be used for signal amplification, for example by surface-enhanced Raman spectroscopy (SERS).

[0047] The total alkalinity absorbed by the buffer layer can also be determined by measuring the total alkalinity absorbed by sub-sections of the buffer layer and subsequently projecting over the entire buffer layer. For example, the step of determining the total alkalinity absorbed by sub-sections of the buffer layer can comprise measuring the pH of a plurality of buffer sub-sections arranged next to each other in a horizontal direction orthogonal to the vertical direction, and subsequently providing an average change in pH of all buffer sub-sections.

[0048] Depending on the application, different alkalinity storage layers, for example buffer layers, can be used. When a buffer layer is used, the buffer layer typically comprises a buffer having a plurality of acidic buffer groups and basic buffer groups. The acidic buffer groups and the basic buffer groups are in equilibrium with each other, and the position of the equilibrium determines the pH of the buffer. Thereby, at an initial pH, the buffer has an initial concentration of acidic buffer groups and an initial concentration of basic buffer groups, and has an initial molar amount of acidic buffer groups and an initial molar amount of basic buffer groups relative to the total molar amount.

[0049] In some variants, the alkalinity storage layer comprises or consists of a buffer layer. The buffer layer can for example have an initial pH of 2 to 6, for example 4 to 6. In some variants, the initial pH is 4 to 5, preferably 4.5 to 4.7. In some variants, the buffer layer comprises a plurality of carboxylic acid groups and a plurality of carboxylate groups.

[0050] In some variants, the alkalinity storage layer (e.g. buffer layer) comprises immobilized buffering agent. In some variants, the alkalinity storage layer (e.g. buffer layer) comprises a bead having a plurality of carboxylic acid groups and a plurality of carboxylate groups on the surface of the bead. The alkalinity storage layer may, for example, comprise DuPont AmberLite MAC-3 H resin or DuPont AmberLite IRC83 H resin, preferably DuPont AmberLite IRC83 H resin.

[0051] The buffer capacity of the buffer layer can be chosen differently depending on the application. The buffer capacity may, for example, be chosen such that it is at least 10%, preferably at least 100%, more preferably at least 500% higher than the target total alkalinity to be absorbed by the buffer layer within the measurement period. In some variants, the buffer capacity may, for example, be at least 2 mol / m 2 , preferably 4.4 mol / m 2 to 568 mol / m 2 , more preferably 10 mol / m 2 to 100 mol / m 2 , even more preferably 44 mol / m 2 . The buffer capacity describes the molar amount of alkalinity that can be absorbed by the buffering agent per unit of surface area (in mm 2 ) that is sampled by the buffer layer. The surface area that is sampled by the buffer layer is typically the surface area of the soil surface from which the soil infiltrate infiltrates into the device, which is typically the surface area of the soil surface below which the device is arranged in vertical direction. In some variants, the surface area that is sampled by the buffer layer corresponds to the surface area of the upstream wall of the device.

[0052] The measurement period can be chosen differently depending on the application. For example, the measurement period can be at least 3 months, preferably 5 to 60 months, more preferably 6 to 24 months.

[0053] The measurement position can be chosen depending on the application. Typically, the measurement position is chosen such that the upstream wall of the device is arranged at least 10 mm below the soil surface. In some variants, the upstream wall of the device is in the measurement position arranged 30 mm to 3’000 mm, preferably 50 mm to 1’000 mm below the soil surface.

[0054] In some variants, the device used in the methods disclosed herein can be labeled as a buffer device. The device comprises an upstream wall and a buffer layer arranged downstream of the upstream wall in the vertical direction. In other words, the buffer layer can be described as arranged downstream of the upstream wall. In some variants, the device further comprises a bottom wall arranged opposite the upstream wall, typically opposite with respect to the vertical direction. The buffer is typically arranged between the upstream wall and the bottom wall. The upstream wall is permeable to water, and if implemented, the bottom wall is typically also permeable to water. In some variants, the upstream wall and / or the bottom wall each comprise a membrane. The upstream wall and / or the bottom wall can each be impermeable to roots and / or insects. Further, the upstream wall and / or the bottom wall can each be impermeable to soil. In some variants, the upstream wall and / or the bottom wall have a through-hole of less than 100 mm 2 , preferably less than 10 mm 2 , more preferably less than 1 mm 2 .

[0055] In some variants, the device further comprises a first interspacing layer arranged between the upstream wall and the alkalinity storage layer in the vertical direction. For example, the first interspacing layer can be directly adjacent to, e.g. contact, the alkalinity storage layer in the vertical direction. The first interspacing layer may, for example, comprise sand, e.g. quartz sand. The first interspacing layer may, for example, have a thickness of at least 2 mm, preferably at least 5 mm, in the vertical direction. In some variants, the first interspacing layer has a higher hydraulic conductivity (e.g. water permeability) than the alkalinity storage layer.

[0056] In some variants, the device further comprises a second interspacing layer (e.g. lower interspacing layer) arranged downstream of the alkalinity storage layer. For example, the second interspacing layer can be arranged below the alkalinity storage layer in the vertical direction, e.g. between the bottom wall and the alkalinity storage layer in the vertical direction. In some variants, the second interspacing layer can be directly adjacent to, e.g. contact, the alkalinity storage layer in the vertical direction. The second interspacing layer may, for example, comprise sand, e.g. quartz sand. The second interspacing layer may, for example, have a thickness of at least 2 mm, preferably at least 5 mm, in the vertical direction. In some variants, the second interspacing layer has a higher hydraulic conductivity (e.g. water permeability) than the alkalinity storage layer, such that backflow of soil infiltrate from the second interspacing layer to the alkalinity storage layer is minimized.

[0057] In some variants, the first interspacing layer can be an upstream interspacing layer, e.g. upper interspacing layer. Alternatively or in combination, the second interspacing layer can be a downstream interspacing layer, e.g. lower interspacing layer. Notably, the device can comprise a second interspacing layer, whether or not it also comprises a first interspacing layer.

[0058] The device typically further comprises a circumferential side wall, which is substantially impermeable to liquid and which extends in the vertical direction from the upstream wall to the bottom wall. The circumferential side wall is arranged circumferentially around the alkalinity storage layer, and, if implemented, around the first and second gap layers. Depending on the application, the circumferential side wall can be coated with an insect repellent and / or a root repellent. The circumferential side wall is typically substantially impermeable to liquid.

[0059] In some variants, the side wall extends in the vertical direction beyond the upstream wall. For example, the side wall can extend into a soil column arranged above the upstream wall in the vertical direction. This can enable the guidance of soil infiltrates, and can facilitate uniform and representative flow of soil infiltrates into the device.

[0060] In some embodiments, the device can comprise a cylindrical tube filled with a buffer layer. The buffer layer may, for example, contain a resin that acts as a buffer for solutions in contact therewith. The buffer resin may, for example, contain chemicals buffered to a relevant pH, for example 4.5. As an example, the buffer layer can comprise carboxylic acid groups and carboxylic acid sodium salts grafted onto polymer (e.g. acrylic, divinylbenzene or styrene) beads, for example effective at a pH of 4.5. Upstream (e.g. upper) and / or downstream (e.g. lower) gap layers, which can consist of quartz sand, can be used to sufficiently separate the buffer medium from the surrounding soil to prevent diffusion back into the device. The membrane is typically permeable to any infiltrates from the topsoil, while ensuring the mechanical integrity of the device. An additional function of the membrane can be to prevent the intrusion of animal and plant root systems.

[0061] The device can be designed such that it allows the flow of soil infiltrates through the inner layers depending on the surrounding soil. In some variants, a passive device is used (i.e. for example without flow management), in other variants, active flow management is used. For example, in some variants, the water pressure on the water column above the device can be controlled to ensure representative flow of soil infiltrates through the device.

[0062] In some variants, the device comprises a flux regulation manifold, for example in the form of a suction plate. The flux regulation manifold can be used to actively regulate the suction, increasing the accuracy of the measurement. Additionally or alternatively, a tensiometer can be used, and a pump system can regulate the vacuum within the device to reflect the surrounding groundwater level.

[0063] Depending on the application, the device can be placed in different measurement locations and / or different soils. In some variants, the step of positioning the device in a measurement location comprises ensuring that the hydrological properties of the soil column arranged vertically above the upstream wall match the hydrological properties of a second reference section of soil arranged horizontally adjacent to the soil column. For example, the step of positioning the device in a measurement location can comprise controlling one or more hydrological parameters of the soil column such that the soil column corresponds to the second reference section in terms of the one or more hydrological parameters. In this context, "corresponds to" can for example mean that the respective hydrological parameter determined for the soil column is within 25%, preferably within 15%, more preferably within 5% of the same hydrological parameter determined for the second reference section. The one or more hydrological parameters can for example include hydraulic conductivity, water potential, water saturation, soil density and / or soil temperature.

[0064] In some variants, the soil is ploughed after positioning the device in a measurement location. The soil can be ploughed before and / or during the measurement period.

[0065] In some variants, positioning the device in a measurement location comprises inserting the device into the measurement location through a lateral installation tunnel. Typically, the device is inserted into the measurement location through the lateral installation tunnel such that the soil column arranged vertically above the upstream wall of the measurement location is substantially unchanged during placement of the device. In particular, the device can be positioned in the measurement location without requiring complete or partial removal of the soil column.

[0066] The methods disclosed herein can for example be used to quantify the amount of carbon dioxide captured in a relevant total area, for example by measuring in a sample area of the relevant total area. Thereby, more generally, the present disclosure relates in a second aspect to a method of determining the amount of carbon dioxide absorbed by a soil infiltrate in a relevant total area. The method can comprise determining the amount of carbon dioxide absorbed by a soil infiltrate in a sample area according to any embodiment of the method of the first aspect disclosed herein. In particular, the measurement location can be arranged vertically below the sample area. Typically, the sample area has a sample surface area that is the same as the surface area of the upstream wall of the device. The total amount of carbon dioxide absorbed by a soil infiltrate in the relevant total area can for example be determined based on the determined amount of carbon dioxide absorbed by a soil infiltrate in the sample area. As an example, the total amount of carbon dioxide absorbed in the sample area can be multiplied by a field factor to provide the total amount of carbon dioxide absorbed in the relevant total area. In some variants, the field factor is the ratio between the surface area of the relevant total area and the surface area of the sample area. Depending on the application, the field factor can also represent further influences, such as the amount of mineral matter deposited on the soil surface, differences in surface topography, etc. In some variants, multiple sample areas are used to determine the amount of carbon dioxide absorbed by a soil infiltrate in the relevant total area.

[0067] The method of the present disclosure can for example be used to determine the amount of carbon dioxide removed from the atmosphere during a measurement period. The amount of carbon dioxide removed from the atmosphere during the measurement period can for example be determined based on the total amount of carbon dioxide absorbed by the soil infiltrate during the measurement period. In some variants, the amount of carbon dioxide removed from the atmosphere during the measurement period can substantially correspond to the total amount of carbon dioxide absorbed by the soil infiltrate during the measurement period. In further variants, the total amount of carbon dioxide absorbed by the soil infiltrate during the measurement period can be multiplied by a correction factor to provide the amount of carbon dioxide removed from the atmosphere during the measurement period, depending on the application. The correction factor can for example take into account the ratio between carbon dioxide absorbed in solid form and the amount of carbon dioxide absorbed by the soil infiltrate, depending on the application. For example, a solid precipitate containing a salt based on carbon dioxide can be formed, which can only partially dissolve and enter the soil as part of the soil infiltrate in some applications.

[0068] In a third aspect, the present disclosure relates to a device, in particular for determining the amount of carbon dioxide generally absorbed by a soil infiltrate over a measurement period. In some embodiments, the device can be used to determine the total alkalinity absorbed by the soil infiltrate over a measurement period.

[0069] Different embodiments of the device have been disclosed in the context of the method according to any embodiment of the first aspect of the present disclosure. These embodiments are also applicable to the third aspect of the present disclosure, i.e. they also constitute possible embodiments of the device. For example, the device can comprise a first wall (which can for example be an upstream wall), a second wall (which can for example be a bottom wall) opposite the first wall, and a buffer layer arranged between the first wall and the second wall in a first direction (which can for example be a vertical direction). The device can further comprise a first gap layer (which can for example be an upstream gap layer, e.g. an upper gap layer) arranged between the first wall and the buffer layer in the first direction. Additionally or alternatively, the device can further comprise a second gap layer (which can for example be a downstream gap layer, e.g. a lower gap layer) arranged between the second wall and the buffer layer in the first direction.

[0070] In the present disclosure, when reference is made to a "device", the device is generally a device for determining the amount of carbon dioxide absorbed by a soil infiltrate, unless explicitly stated otherwise or unless the context explicitly dictates otherwise.

[0071] In some variants, the device comprises a housing comprising a water-permeable upstream wall and a water-permeable downstream wall, both defining a permeation flow path. The water-permeable upstream wall and the water-permeable downstream wall are typically arranged opposite to each other. The permeation flow path can for example extend parallel to the vertical direction. It will be appreciated that the microscopic permeation flow path can be tortuous. However, on a macroscopic scale, the permeation flow path can be substantially linear and in some variants can be substantially parallel to the vertical direction. In some variants, the water-permeable upstream wall can be denoted as the water-permeable inlet wall of the housing and the water-permeable downstream wall can be denoted as the water-permeable outlet wall of the housing. Typically, the flow path extends through the housing.

[0072] In some variants, the device further comprises an alkalinity storage layer arranged along the permeation flow path between the upstream wall and the downstream wall. The alkalinity storage layer is formed of a material bearing a plurality of acidic groups on its surface, such that at least a portion of the acidic groups are deprotonated when a soil permeate comprising aqueous bicarbonate ions and / or aqueous carbonate ions permeates through the alkalinity storage layer.

[0073] Typically, the alkalinity storage layer is configured such that the soil permeate can permeate and / or trickle through the alkalinity storage layer. Typically, the soil permeate is able to pass through the alkalinity storage layer but still remains long enough to allow at least a portion of the acidic groups to be deprotonated upon contact with the soil permeate comprising aqueous bicarbonate ions and / or aqueous carbonate ions. For example, in some variants, the alkalinity storage layer has a hydraulic conductivity similar to sand (e.g. coarse sand, fine sand or silt), soil, loam, clay loam or clay. In some variants, the alkalinity storage layer has a hydraulic conductivity that is at least 10%, preferably at least 50%, more preferably at least 70% higher than the hydraulic conductivity of sand (e.g. coarse sand, fine sand or silt), soil, loam, clay loam or clay. In some variants, the soil (e.g. the soil in which the device is located in the method according to the present disclosure) has a hydraulic conductivity (Ks) as determined for example according to ASTM D2434-22 of 1 to 1500 cm / day, preferably 5 to 500 cm / day, more preferably 10 to 100 cm / day. Alternatively or in combination, in some variants, the alkalinity storage layer has a hydraulic conductivity (Ks) as determined for example according to ASTM D2434-22 of 1 to 4000 cm / day, preferably 100 to 2000 cm / day, more preferably 1000 to 1500 cm / day. Typically, the hydraulic conductivity is determined under standard conditions, including at room temperature.

[0074] The devices described herein can be used in a number of applications. For example, the devices can be configured for quantifying the amount of carbon dioxide absorbed by a soil infiltrate over a measurement time period. For example, the amount of carbon dioxide absorbed in an enhanced weathering process can be quantified. In some variants, the devices are subsurface devices, i.e. the devices are configured to be installed and maintained underground at least during the measurement time period, preferably permanently.

[0075] In some variants, the device comprises a second sensor interconnected with the alkalinity storage layer and configured to measure the protonation state of the acidic groups over at least a part of the measurement time period. Depending on the application, the protonation state of the acidic groups can be measured directly or indirectly. For example, the protonation state can be measured using a pH meter, or the protonation state of the acidic groups can be measured using other more indirect sensors. Depending on the application, the protonation state of the acidic groups over at least a part of the measurement time period can be measured in different ways. For example, the degree or extent of deprotonation can be measured over the entire measurement time period or over the entire part, or the deprotonation profile can be measured over time.

[0076] In some variants, the material forming the alkalinity storage layer is a material that changes its volume expansion when a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions penetrates through the alkalinity storage layer. For example, in some variants, the material forming the alkalinity storage layer is a swellable and / or shrinkable material, in particular a swellable and / or shrinkable material when a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions penetrates through the alkalinity storage layer. More preferably, in some variants, the material forming the alkalinity storage layer is swellable and / or shrinkable upon at least partial deprotonation of the acidic groups.

[0077] It is to be understood that the term "material forming the alkalinity storage layer" as used herein generally refers to the main material forming the alkalinity storage layer, i.e. the material predominantly determining the physical properties of the alkalinity storage layer and / or constituting the majority (e.g. more than 50 wt%, preferably more than 75 wt%, more preferably more than 90 wt%, even more preferably more than 95 wt%, even more preferably substantially 100 wt%) of the alkalinity storage layer by weight. For example, in some variants, the alkalinity storage layer can consist only of the material forming the alkalinity storage layer. In other variants, the alkalinity storage layer can further comprise one or more other materials, which preferably make up less than 25 wt%, more preferably less than 20 wt%, more preferably less than 5 wt% of the alkalinity storage layer.

[0078] In some variants, the alkalinity storage layer contacts the first side of the detection wall, such that a volume expansion change of the material forming the alkalinity storage layer causes a strain on the detection wall and / or a physical deformation of the detection wall. These variants allow for a high precision determination of the amount of carbon dioxide. Depending on the application, different detection walls can be used. For example, in some variants, the detection wall can be a detection membrane and / or a detection sheet and / or a detection membrane and / or a detection plate. Typically, the detection wall is substantially water-impermeable.

[0079] Typically, the alkalinity storage layer contacts the first side of the detection wall with a side surface of the alkalinity storage layer. In some variants, the detection wall extends at an angle of -30° to +30°, preferably -15° to +15°, with respect to the flow direction of the permeate flow path. In some variants, the detection wall extends substantially parallel to the flow direction of the permeate flow path. The variants described in this paragraph can in particular refer to the macroscopic flow direction.

[0080] In some variants, the detection wall completely or partially circumferentially surrounds the alkalinity storage layer. For example, in some variants, the detection wall completely circumferentially surrounds the alkalinity storage layer. In further variants, at least one circumferential section of the alkalinity storage layer is in contact with the detection wall. For example, in some variants, the device comprises a circumferential boundary wall circumferentially surrounding the alkalinity storage layer. The circumferential boundary wall can comprise a detection portion forming the detection wall and a non-detection portion. The non-detection portion typically has a higher bond stiffness than the detection portion forming the detection wall. When the alkalinity storage layer swells and / or shrinks (or other change of volume expansion), the detection portion forming the detection wall can physically deform or strain, while the non-detection portion is substantially unaffected. In some variants, the circumferential boundary wall has an elliptical, preferably circular, cross-section. For example, the detection portion forming the detection wall can have a cross-section forming a circular section.

[0081] The detection wall can optionally be connected to a support frame. For example, the upper edge and / or the lower edge of the detection wall can be connected to a support frame, for example in order to control the physical deformation of the detection wall.

[0082] Depending on the application, different alkalinity storage layers can be used. In some variants, the detection wall is elastically deformable. Thereby, a volume expansion change of the material forming the alkalinity storage layer can cause a physical deformation of the detection wall. In some variants, the detection wall is elastically deformable by elastically bulging outwards of the detection wall on a second side of the detection wall opposite to the first side of the detection wall. In some variants, the detection wall is an elastic membrane. In some variants, the detection wall has a lower bending stiffness than the side wall of the housing.

[0083] In some variants, the device comprises a first sensor for measuring the change in volume expansion of the material forming the alkalinity storage layer for at least a part of the measurement time period. The first sensor may, for example, comprise a sensor for measuring the strain on the detection wall and / or the physical deformation of the detection wall. The first sensor may, for example, be an optical sensor for measuring the physical deformation (e.g. outward bulging) of the detection wall. Depending on the application, the device can comprise a plurality of first sensors. For example, the device can comprise two different optical sensors, e.g. measuring the physical deformation from different angles, e.g. in order to improve accuracy. The device can also comprise two different types of first sensors, e.g. a mechanical sensor and an optical sensor.

[0084] In some variants, the first sensor comprises a strain gauge interconnected to the detection wall. Alternatively or in combination, the first sensor can comprise a piezoelectric sensor interconnected to the detection wall.

[0085] In some variants, the alkalinity storage layer comprises a plurality of sub-layers arranged behind each other along the permeate flow path. Thereby, the sub-layers are typically arranged such that the soil permeate successively permeates through different sub-layers when permeating through the alkalinity storage layer. For example, the sub-layers can be arranged underneath each other in a vertical direction. Depending on the application, the different sub-layers are made of the same material or of different materials.

[0086] In some variants, the device comprises a plurality of first sensors, wherein each sub-layer is interconnected with a respective first sensor for measuring the change in volume expansion of the material forming the respective sub-layer for at least a part of the measurement time period. These variants can advantageously be used to improve the accuracy of the measurement results. Furthermore, additional information about the permeation profile and the penetration depth over time can be obtained.

[0087] Depending on the application, different alkalinity storage layers can be used. For example, in some variants, the plurality of acidic groups has a pKa of less than 6.35, preferably 2 to 6, more preferably 3 to 6. In some variants, the plurality of acidic groups has a pKa of higher than 2. As used herein, the pKa value typically refers to aqueous conditions, unless explicitly stated otherwise or unless the context explicitly provides otherwise. In some variants, the plurality of acidic groups are carboxylic acid groups and / or sulfonic acid groups, preferably carboxylic acid groups.

[0088] In some variants, the housing further comprises a substantially water-impermeable side wall circumferentially surrounding the alkalinity storage layer. In some variants, the side wall circumferentially surrounds the alkalinity storage layer along the entire height of the alkalinity storage layer. The height of the storage layer generally refers to the maximum extension of the alkalinity storage layer in the vertical direction. In some variants, the water-impermeable side wall extends from the upstream wall to the downstream wall. Depending on the application, the side wall can fully or partially contact the alkalinity storage layer, or not contact the alkalinity storage layer at all.

[0089] In some variants, the side wall has an elliptical, preferably circular, cross-section. The side wall may, for example, have a hollow cylindrical shape. In some variants, the side wall has a compressive strength of at least 0.1 MPa, preferably 0.2 to 20 MPa, more preferably 0.5 to 10 MPa, more preferably 1 to 5 MPa, as determined, for example, according to ISO 604, version 2002.

[0090] In some variants, the alkalinity storage layer comprises a buffer. For example, in some variants, the alkalinity storage layer is a buffer layer having an initial pH of 3 to 7. The buffer layer may, for example, be arranged below the upstream wall, e.g. the top wall, in the vertical direction. The buffer layer may, for example, be configured to change its pH over a measurement time period when a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions penetrates through the buffer layer.

[0091] In some variants, the initial pH of the buffer is 4 to 5, preferably 4.5 to 4.7. Alternatively or in combination, the buffer layer can comprise beads having a plurality of carboxylic acid groups and a plurality of carboxylate groups on the surface of the beads. In some variants, the buffer layer has a buffer capacity of at least 2 mol / m 2 , preferably 4.4 mol / m 2 to 568 mol / m 2 , more preferably 10 mol / m 2 to 100 mol / m 2 , even more preferably 44 mol / m 2 .

[0092] In some variants, the device further comprises a pH detector configured for measuring the pH and / or the pH change of the alkalinity storage layer over at least a portion of the measurement time period.

[0093] In some variants, the alkalinity storage layer comprises a resin, preferably an ion exchange resin, wherein the resin is swellable and / or contractible upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions. In some variants, the resin comprises a plurality of beads (e.g. having a radius of less than 10 mm, such as less than 2 mm). The resin may, for example, comprise a plurality of pores that are typically arranged randomly. The pores may, for example, allow the permeate to permeate through the alkalinity storage layer. The pores may, for example, have a slit width of less than 1’000 nm, preferably less than 500 nm, more preferably less than 100 nm. In some variants, the pores have a slit width of 0.01 nm to 100 nm, such as 0.5 nm to 70 nm.

[0094] Depending on the application, the housing can have different dimensions, geometrical properties and shapes. In some variants, the upstream wall and / or the downstream wall has a through hole having a cross section of less than 100 mm 2 , preferably less than 10 mm 2 , more preferably less than 1 mm 2 . It is to be understood that in at least some embodiments, all through holes in the upstream wall and / or the downstream wall each have a cross section of less than 100 mm 2 , preferably less than 10 mm 2 , more preferably less than 1 mm 2 .

[0095] In some variants, the device further comprises a first permeate flow guiding structure arranged on the upstream side of the upstream wall and configured to guide a permeate flow towards the upstream wall. The first permeate flow guiding structure may, for example, be arranged on the upstream side of the upstream wall and can optionally face away from the alkalinity storage layer. Thereby, the first permeate flow guiding structure may, for example, in some variants be used to feed and / or deliver a representative permeate flow to the upstream wall of the device. In some variants, the first permeate flow guiding structure comprises a water-impermeable wall extending substantially parallel to the side wall of the housing. The first permeate flow guiding structure may, for example, extend substantially parallel to the vertical direction. For example, the first permeate flow guiding structure can extend from the upstream wall away from the alkalinity storage layer in the vertical direction.

[0096] In some variants, the first permeate flow guiding structure extends away from the upstream wall. In some variants, the first permeate flow guiding structure can circumferentially surround the upstream wall.

[0097] In some variants, the permeate flow guiding structure has substantially the same cross-sectional profile as the side wall of the housing. In some variants, the cross-sectional area of the permeate flow guiding structure is substantially the same as the cross-sectional area of the upstream wall. These variants can for example be advantageous to ensure that the permeate flow exposing the device is representative and substantially corresponds to the cross-section of the soil portion being examined by the device. In other words, the permeate flow guiding structure can serve to minimize or even prevent undesired lateral flow of the permeate upstream of the upstream end. Such lateral flow can lead to measurement distortions, for example, leading to a permeate flow reaching the device that is too small or too large compared to the permeate flow that would be appropriate for a given soil cross-section.

[0098] In some variants, the device further comprises a second permeate flow guiding structure, which can for example be configured to direct the permeate flow towards and / or away from the alkalinity storage layer. For example, the second permeate flow guiding structure can for example be arranged adjacent to and / or proximate to the upstream wall. For example, the second permeate flow guiding structure can be configured to control the ratio between the permeate flow entering through the upstream wall and the permeate flow permeating through the alkalinity storage layer. The second permeate flow guiding structure can for example extend at an angle of 1° to 90°, preferably 5° to 75°, more preferably 5° to 45°, with respect to the horizontal direction. In some variants, the second permeate flow guiding structure can comprise a slope or another feed structure arranged along the permeate flow path between the upstream wall and the alkalinity storage layer. For example, the slope angle of the slope can serve to feed the permeate flow to the alkalinity storage layer, for example in cases where the alkalinity storage layer can have a smaller and / or different cross-section compared to the upstream wall. In some variants, the slope angle of the slope can also be set such that at least a portion of the permeate flow is directed away from the alkalinity storage layer, for example to a bypass channel that bypasses the alkalinity storage layer. This can for example serve to prevent overfilling of the alkalinity storage layer. In some variants, the second permeate flow guiding structure is arranged above and / or below the dry compartment of the device in the vertical direction. In some variants, the second permeate flow guiding structure is arranged between the upstream wall and the dry compartment. The dry compartment can for example be configured to house one or more of: a second sensor, a first sensor, a first communication unit, a sensor processing unit, or a power supply. The dry compartment can be configured such that soil permeate does not enter (for example permeate) into the dry compartment. The dry compartment can for example be arranged adjacent to (for example adjacent to in the horizontal direction) the wet compartment housing at least the alkalinity storage layer. In some variants, a detection wall is arranged between the dry compartment and the wet compartment. In some variants, the dry compartment comprises a maintenance door.

[0099] More generally, in some variants, the device comprises a bypass channel bypassing at least a portion of the alkalinity storage layer. In some variants, the bypass channel bypasses the alkalinity storage layer completely. The bypass channel can for example extend parallel to the alkalinity storage layer with respect to the direction of the permeate flow path. For example, the bypass channel can extend from an upstream side of the alkalinity storage layer to a downstream side of the alkalinity storage layer.

[0100] In some variants, the device comprises a downstream gap layer (e.g. a lower gap layer) arranged along the flow path downstream of the buffer layer and having a higher hydraulic conductivity than the alkalinity storage layer, such that backflow of soil permeate from the second gap layer to the alkalinity storage layer is minimized.

[0101] In some variants, the device further comprises a wick drain layer arranged in the permeate flow path downstream of the alkalinity storage layer. The wick drain layer can for example be configured for consolidating soil permeate.

[0102] In some variants, the device further comprises a root barrier layer, which can for example comprise trifluralin. In some variants, the device further comprises a first barrier layer, which can for example be configured to prevent insects from passing and / or configured to prevent clogging. The first barrier layer can for example consist of a powder and / or fine particles, preferably having a particle size of no more than 3 mm, preferably no more than 1 mm, more preferably no more than 0.1 mm. In some variants, the first barrier layer comprises or consists of diatomaceous earth. Preferably, the root barrier layer and / or the first barrier layer are arranged upstream of the alkalinity storage layer.

[0103] In some variants, the device further comprises a first glass fiber filter layer, and optionally further comprises a second glass fiber filter layer. Preferably, the first glass fiber filter layer is arranged upstream of the alkalinity storage layer. Alternatively or in combination, the first glass fiber filter layer can be arranged upstream of the root barrier layer.

[0104] In some variants, the device further comprises a maintenance door allowing access to the device, preferably to the alkalinity storage layer. The maintenance door can for example be arranged in a side wall of the housing. The maintenance door can for example be implemented as a maintenance hatch.

[0105] In some variants, the device can further comprise a flow control unit configured to control the internal flow of soil penetrant penetrating through the device such that the internal flow has a known or determinable flow ratio relative to the external flow of soil penetrant penetrating through a first reference section of soil arranged outside the device. For example, in some variants, the flow control unit is configured to control the internal flow of soil penetrant penetrating through the device such that the internal flow substantially maintains a predetermined flow ratio relative to the external flow of soil penetrant penetrating through a first reference section of soil arranged outside the device. The predetermined flow ratio can for example be 1 :5 to 5:1, preferably 1 :2.5 to 2.5:1. In some variants, the device can comprise a flow control unit configured to control the internal flow of soil penetrant penetrating through the device such that the internal flow substantially corresponds to the external flow of soil penetrant penetrating through a first reference section of soil arranged outside the device. Other embodiments of this variant are disclosed hereinabove. For example, the flow control unit can comprise a pump for controlling the vacuum pressure inside the device. Additionally or alternatively, the flow control unit can comprise a tensiometer.

[0106] In a fourth aspect, the disclosure relates to a system for determining the amount of carbon dioxide absorbed by soil penetrant. The system comprises any embodiment of the device described herein, i.e. any embodiment of the device for determining the amount of carbon dioxide absorbed by soil penetrant. When used in the system, a variant of the device is used, wherein the device further comprises a first communication unit configured to transmit the underground measurement data measured during at least a part of the measurement period. Typically, the device is further configured to be installed in the underground soil.

[0107] The system further comprises a second communication unit configured to receive the underground measurement data. The second communication unit is typically configured to be installed above ground. The second communication unit can optionally be configured to transmit the received underground measurement data, for example, to another unit, such as a processing unit. In some variants, the second communication unit is a transceiver unit. The second communication unit can for example be installed locally in order to transmit the underground measurement data to a remotely located processing unit, such as a server.

[0108] The system further comprises a processing unit configured to determine the total alkalinity absorbed by the alkalinity storage layer during the measurement period based on the underground measurement data. Typically, the processing unit is configured to be installed above ground.

[0109] The system can for example be used to permanently install the device in the ground without the need to excavate or dig the device to determine the amount of carbon dioxide absorbed by the soil infiltrate. This is particularly advantageous because it is less labor intensive and because excavating or digging can endanger the soil and can endanger the accuracy of the measurements.

[0110] The system described herein can for example be a carbon capture quantification system, for example for quantifying the amount of carbon dioxide captured in an enhanced weathering process.

[0111] In a fifth aspect, the disclosure relates to the use of the device or the system for determining the amount of carbon dioxide absorbed by the soil infiltrate, preferably in an enhanced weathering process. More specifically, any embodiment of the device described herein can be used, i.e. any embodiment of the device for determining the amount of carbon dioxide absorbed by the soil infiltrate. Similarly, any embodiment of the system described herein can be used, i.e. any embodiment of the system for determining the amount of carbon dioxide absorbed by the soil infiltrate by the system.

[0112] It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments and, together with the description, serve to explain the principles and operation of the concepts disclosed.

[0113] In the present disclosure, for reasons of clarity and conciseness, directional references are provided at least partly according to vertical and horizontal directions. These are generally referring to the directions of a compass, i.e. horizontal generally means parallel to the flat part of the earth’s surface, and vertical generally means towards the sky. In the vertical direction, generally, indications such as “up”, “upper” or “top” refer to the vertical direction towards the sky, and indications such as “down”, “lower” or “bottom” refer to the vertical direction towards the core of the earth. Relative indications, i.e. indications indicating a relative arrangement in the vertical direction, can optionally be specified relative to the assumed flow of the soil infiltrate, which can be assumed to flow in the vertical direction towards the core of the earth. A relative indication such as “upper” or “above in the vertical direction” can optionally be replaced by the indication “upstream”, and a relative indication such as “lower”, “below in the vertical direction”, “down in the vertical direction” or “downward in the vertical direction” can optionally be replaced by the indication “downstream”. It will be understood that, unless explicitly stated otherwise or unless the context explicitly dictates otherwise, the terms “upstream” and “downstream” refer to the infiltration flow path. In particular, they generally refer to the macroscopic flow path of the soil infiltrate.

[0114] SUMMARY The application described herein will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: Figure 1 shows an embodiment of a method for determining the amount of carbon dioxide absorbed by a soil percolate; Figure 2 A flow chart showing the embodiment shown in Figure 1 is shown; Figure 3 The change in pH of the alkalinity storage layer in the presence of a soil percolate having a higher pH than the alkalinity storage layer (arrow B), and correspondingly a lower pH than the alkalinity storage layer (arrow A) is shown; Figure 4 shows simulated data for the difference in pH between a soil percolate stream and an alkalinity storage layer (e.g. a buffer resin) Figure 4A ) and the integrated signal over time Figure 4B ); Figure 5 An embodiment of a device with active flow control is shown; Figure 6 An embodiment of a device comprising a sensor for measuring the change in volume expansion of the material forming the alkalinity storage layer is shown; Figure 7 shows a variant of the device shown in Figure 6 which further comprises a plurality of sub-layers of the alkalinity storage layer; Figure 8 shows the swelling of the alkalinity storage layer due to the penetration of a soil percolate through the alkalinity storage layer; Figure 9 shows an embodiment of a device comprising a dry compartment arranged outside the side wall of the housing; Figure 10 An embodiment of a system for determining the amount of carbon dioxide absorbed by a soil percolate is shown. DETAILED DESCRIPTION Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In actual practice, the embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or like elements.

[0116] Figures 1 and 2 show embodiments of the method disclosed herein. In particular, in a first step (S1, see Figure 1A) the device 3 is placed within the project area, directly below the soil surface 21, typically 30 cm below the soil surface 21. The device 3 is oriented with a permeable upstream wall 5 parallel to the ground and an opposite permeable downstream wall 8 (which can for example be a bottom wall) to ensure a sufficient and representative flow profile. The surrounding medium can have been altered during installation of the device to mimic the hydrological properties of the surrounding soil 2 (for example by embedding the device 3 in sand / silt) in such a way that it is backfilled. In addition, the device 3 comprises a buffer layer 6 sandwiched between an upper gap layer 12 and a lower gap layer 11.

[0117] In addition, mineral matter 4 is provided on or near the soil surface 21. The mineral matter 4 can have been present prior to installation of the device 3, or the mineral matter is provided separately. The amount of pre-existing mineral matter 4 can also be increased. The mineral matter 4 can thus be provided prior to, simultaneously with, or after installation of the device.

[0118] In a second step (S2, see Figure 2 A) during the project, the soil infiltrate 1 is transported through the device 3. During this period, the pH of the soil infiltrate 1 is buffered to the target pH (4.5) by the active components on the bead surface of the buffer layer 6. As Figure 3 illustrated, during the process, the relative ratio of acidic (AH) and basic (A – ) sites on the bead surface of the buffer layer 6 changes depending on the exchanged species. Figure 3 In the middle is shown the buffer layer 6 before the start of the project. For most agricultural fields, the soil infiltrate 1 has a pH > 4.5, which leads to a gradual deprotonation of the acidic surface groups, as shown in process (B) in Figure 3 In contrast, theoretically, if the pH of the soil infiltrate 1 is lower than the pH of the buffer layer 6, this will lead to a protonation of the buffer layer 6, as shown in process (A) in Figure 3

[0119] Again with reference to Figures 1 and 2, during the project, the alkalinity of the buffer layer 6 generally becomes higher and higher. More specifically, the alkalinity of the soil infiltrate 1 (which at least partly originates from the capture of carbon dioxide from the air) is effectively absorbed and stored by the buffer layer 6. Given the flow direction of the soil infiltrate 1, the buffer layer 6 can have a complex pH profile over its entire volume. For example, the top sublayer 6a of the buffer layer 6 can have the highest (i.e. highest alkalinity) pH compared to the other sublayers 6a, 6b of the buffer layer 6. In some variants, the pH decreases from the top sublayer 6a to the bottom sublayer.

[0120] In a third step (S3, see Figure 1C ​) after the project, or at the latest 12 months after installation, the device 3 is recovered from the soil 2. The buffer layer 6 in the device is divided into a number of vertical slices (i.e. e.g. sub-layers 6a, 6b). The slices are homogenized and an aliquot is taken for quantification. The aliquot is dispersed in about four times the amount of DI water and the pH is continuously measured by a pH meter. Subsequently, an aqueous solution of NaOH is titrated into the mixture until it reaches a reference pH (e.g. pH = 7). The amount of NaOH consumed is compared to a reference slice prepared without exposure to the soil infiltrate 1. The difference between the two is then the amount of TA previously captured in the aliquot. The process is repeated for the slices from the top until no additional TA is detected. If this does not happen, the device 3 has been oversaturated and only provides a lower bound on the total alkalinity infiltrated. If the pH profile within the device, as determined by the pH of the slices, is not monotonically decreasing from top to bottom, upflowing currents can have brought solutes into the device 3 from below. In such a case, the device 3 can be damaged and can have to be discarded. For intact devices 3, the sum over the analyzed slices can provide the total alkalinity absorbed by the buffer layer over the area covered by the device 3. The total alkalinity absorbed projected on the relevant project area thus gives the total alkalinity infiltrated at the project site.

[0121] Optionally, to quantify the carbon capture enhanced by weathering activities, any total alkalinity captured by the same method in an appropriate control site is subtracted to give the additional total alkalinity produced by the enhanced weathering project activities. The total alkalinity value thus determined is a first quantification of the carbon removal resulting from the project activities. Additional corrections can be made to the process as outgassing.

[0122] It will be appreciated that the total alkalinity absorbed by the buffer layer 6 during the project can be determined in many different ways and is not limited to pH measurements. For example, conductivity measurements are also possible. As an example, an aliquot can be dispersed and the conductivity can be measured. A reference calibration curve can then provide an accurate determination of the ion concentration. In some variants, the aliquot is dispersed and an excess of salt (e.g. NaCl) is added. The Na + Any other ions bound to the surface of the beads are displaced by the ions. After draining and repeated rinsing of the beads solids with DI water, the aliquot is re-dispersed and the conductivity is measured.

[0123] In further variants, the aliquot can be digested e.g. with hydrochloric and nitric acid and the released ions are measured using ICP-MS. The additional cations captured compared to a reference device directly correspond to the additional TA produced by the EW.

[0124] Figure 4 shows simulated data for the difference in pH between a soil infiltrate stream and a buffer resin (top panel) Figure 4A ) and the integrated signal over time (bottom panel)Figure 4B ). Effectively, the fidelity of the measurement can be improved by integrating the signal (e.g. the pH differential) over the duration of the project. In particular, while it can be difficult to measure the pH differential that occurs over time in an instantaneous manner and is prone to measurement error, accumulating the pH differential over time (e.g. by allowing the buffer layer 6 to absorb the alkalinity of the percolating flow and effectively store it over time) allows the pH differential to be integrated over time, which allows the total alkalinity of the soil percolate to be more accurately determined over time. In Figure 4A , the horizontal x-axis represents time (in a.u.) and the vertical y-axis represents the change in pH (ΔpH, in a.u.). In Figure 4B , the horizontal x-axis represents time (in a.u.) and the vertical y-axis represents the integrated alkalinity (a.u.).

[0125] In some variants, the ions flowing through the device 3 can be stored and subsequently released intermittently, in order to convert a continuous flow of low concentration into pulses with increased concentration. This can allow greater measurement accuracy to be obtained.

[0126] In some variants, the signal caused by the relevant ions can be measured by absorption in the visible or infrared, possibly using interferometry, plasma enhancement, evanescent waves or other signal amplification.

[0127] Figure 5 A variant is shown in which, based on a moisture sensor 13 (e.g. a tensiometer) and a pump 14, the pressure exerted on the water column arranged inside the soil column 9 above the device is regulated by a soil percolate collection assembly (e.g. a suction plate) arranged in the surface soil. This ensures that the soil percolate 1 that percolates through the device is representative of the surface area covered.

[0128] Figure 6 Another variant of the device 3 is shown, which also comprises a second sensor 30 interconnected with the alkalinity storage layer 6. The second sensor 30 is configured to measure the protonation state of the acidic groups of the alkalinity storage layer 6 for at least a portion of the measurement period. In the embodiment shown, the second sensor 30 is a pH meter.

[0129] Figure 7 shows an embodiment of the device 3 in which Figure 7B A variant is shown in which Figure 7AA partial close-up of the device 3 is shown. The device 3 comprises a housing 15 having a hollow cylindrical shape with a circular cross-section. The device 3 further comprises an upstream wall 5 and a downstream wall 8 arranged downstream of the upstream wall 5, i.e. vertically below the upstream wall 5. Between the upstream wall 5 and the downstream wall 8, a basicity storage layer 6 is arranged. The basicity storage layer 6 is circumferentially surrounded by a sidewall 18 of the housing 15. In the hollow cylindrical housing 15, a dry compartment 27 is arranged, which accommodates electronic components of the device 3. The dry compartment 27 is thus configured to accommodate the electronic components to protect them from the influence of penetrating water. More specifically, a detection wall 16 is arranged within the housing, which contacts the basicity storage layer 6 on a first side 161 thereof. On an opposite second side 162 facing the dry compartment 27, a plurality of first sensors 17a, 17b is arranged, which are piezoelectric sensors in the shown embodiment. Furthermore, the dry compartment 27 also accommodates a first communication unit 20, which is interconnected with the piezoelectric sensors 17a, 17b and configured to transmit raw sensor data from these sensors to a further communication unit, e.g. a communication unit arranged outside of the device, preferably arranged on the ground (not shown). The dry compartment 27 further accommodates a power supply 24 and a sensor processing unit 25 for processing the raw sensor data. Above the dry compartment 27, a second permeate flow guiding structure 29 feeds the introduced permeate to the basicity storage layer 27 to ensure that the basicity storage layer 27 captures the entire cross-section of the soil, i.e. the soil permeate from the entire column, which is surrounded by the upstream portion of the sidewall 18 in the operational state. In the shown embodiment, the second permeate flow guiding structure 29 is realized as a ramp-like structure.

[0130] An upstream gap layer 12 and a downstream gap layer 11 are arranged upstream and downstream of the basicity storage layer 6, respectively. They separate the basicity storage layer from the adjacent soil, thereby minimizing the risk of contamination of the basicity storage layer 6. Furthermore, the upstream and downstream gap layers 12, 11 each have a higher hydraulic conductivity than the basicity storage layer 6, which prevents backflow of the permeate in the upstream direction.

[0131] In the illustrated embodiment, the alkalinity storage layer 6 is made of a swellable resin. More specifically, the resin comprises a plurality of carboxylic acid groups and carboxylate groups on its surface, and the resin is swellable upon contact with a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (respectively, their corresponding salts). When a soil filtrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (more specifically, their corresponding salts) infiltrates through the resin, the resin swells. The swelling of the resin can be measured using the first sensors 17, in particular by the plurality of first sensors 17a, 17b, which in the illustrated embodiment are piezoelectric sensors. The piezoelectric sensors measure the strain on the detection wall 16 caused by the swelling of the resin, which in turn occurs upon infiltration of the soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (more specifically, their corresponding salts) through the resin. In particular, since the bending stiffness of the detection wall 16 is significantly lower than the bending stiffness of the side wall 18 of the housing 15, the swelling of the resin almost exclusively causes strain on the detection wall 16. The extent of the strain can thus be used to determine the extent of the swelling. Thereby, the extent of the swelling is determined by measuring the extent of the strain by the plurality of first sensors 17a, 17b, which in turn is used to determine the total alkalinity of the soil infiltrate, which in turn is used to determine the amount of captured carbon dioxide.

[0132] Figure 7B A close-up of selected parts of the device 3 is shown. In particular, the close-up shows the detection wall 16 contacting the alkalinity storage layer 6 on its first side 161. On the second side 162 of the detection wall 16, the first sensors 17a, 17b are arranged, which are capable of measuring the strain on the detection wall 16 due to the swelling of the alkalinity storage layer 6.

[0133] It will be appreciated that the swelling of the alkalinity storage layer 6 can cause strain on the detection wall 16 (as explained above) and / or cause the detection wall 16 to bulge outwards. For example, when the detection wall 16 has a low bending stiffness, the bulging outwards can prevail, such that the swelling mainly causes the bulging outwards. In some variants, the detection wall 16 experiences both strain and bulging outwards due to the swelling of the alkalinity storage layer 6. Thereby, it will be appreciated that the sensors 17a, 17b can be configured to determine both the strain and / or the bulging outwards on the detection wall 16. Depending on the application, the detection wall 16 can be selected accordingly. For example, in the illustrated embodiment, the detection wall 16 is made of an elastic membrane.

[0134] Figure 8 shows an embodiment of the device 3 similar to the embodiment shown in Figure 7. In addition, Figure 8 shows that the alkalinity storage layer 6 comprises a plurality of sub-layers 6a, 6b arranged next to each other along the permeation flow path. More specifically, as shown, the sub-layers 6a, 6b are arranged next to each other in a vertical direction, such that the soil permeate permeates successively through the sub-layers 6a, 6b. For each of the sub-layers 6a, 6b, the device 3 further comprises a respective first sensor 17a, 17b configured to detect a strain and / or outward bulging on the detection wall 16 due to swelling of the respective sub-layer 6a, 6b. Accordingly, the first sensors 17a, 17b are also arranged next to each other in the vertical direction. Similar to Figure 7, Figure 8 also shows a partial close-up of the device shown in Figure 8B Figure 8A

[0135] Figure 9 shows the swelling of the alkalinity storage layer 6 due to the permeation of the soil permeate through the alkalinity storage layer. More specifically, a close-up of the device 3 shown in Figure 7 is shown in Figure 9. In Figure 9A the alkalinity storage layer 6 made of swellable resin is shown in an unswollen state. When carbon dioxide reacts with water on the surface of the mineral, a soil permeate comprising aqueous bicarbonate ions and / or aqueous carbonate ions, respectively their respective salts, is formed, which permeates through the soil and eventually through the alkalinity storage layer 6. When the soil permeate starts to permeate into the alkalinity storage layer 6 on the upstream side, the acidic groups on the surface of the alkalinity storage layer 6 are deprotonated, which leads to swelling of the resin, as shown in Figure 9B Due to the higher bending stiffness of the side wall 18 of the housing 15 than the detection wall 16, the detection wall 16 bulges outwardly due to the swelling of the resin, as shown in Figure 9B the alkalinity storage layer 6 made of swellable resin is shown in an unswollen state. When carbon dioxide reacts with water on the surface of the mineral, a soil permeate comprising aqueous bicarbonate ions and / or aqueous carbonate ions, respectively their respective salts, is formed, which permeates through the soil and eventually through the alkalinity storage layer 6. When the soil permeate starts to permeate into the alkalinity storage layer 6 on the upstream side, the acidic groups on the surface of the alkalinity storage layer 6 are deprotonated, which leads to swelling of the resin, as shown in

[0136] Figure 10 Figure 10 shows an embodiment of the device 3, wherein the dry compartment 27 is arranged on the outside of the side wall 18 of the housing 15. More specifically, the side wall 18 together with the detection wall 16 defines a hollow cylindrical shape enclosing the alkalinity storage layer 6, on the upstream side of which the hollow cylinder formed by the upstream portion of the side wall 18 encloses a cylinder which will be the soil column 9 during operation. Although Figure 10 the device 3 itself is shown in a non-operational state and without any soil, for the sake of clarity and to help understanding, in Figure 10 ​​The reference number 9 of the soil column 9 is still shown. In the cross-sectional view, the cross-section of the soil column 9 is essentially the same and flush with the cross-section of the alkalinity storage layer 6. The hollow cylindrical shape formed by the side wall 18 and the detection wall 16 defines a wet compartment 28 of the device 3, which is configured to be exposed to the soil infiltrate.

[0137] In contrast, the dry compartment 27, which accommodates for example the first sensor 17, is arranged outside the hollow cylindrical shape formed by the side wall 18 and the detection wall 16. More specifically, the first sensor 17 is arranged on the second side 162 of the detection wall 16 opposite the first side 161 contacting the alkalinity storage layer 6. Since the dry compartment 27 is arranged outside the housing 15, it further comprises an outer wall itself, including an angled upstream and downstream wall. The inclination angle of the upstream and downstream wall allows to direct the soil infiltrate in a direction away from the side wall 18 of the housing 15.

[0138] Figure 11 An embodiment of a system 19 for determining the amount of carbon dioxide absorbed by the soil infiltrate within a measurement period is shown. More specifically, the system 19 comprises a device 3 as shown in the previous figures. The device 3 further comprises a first communication unit 20 configured to transmit the measurement data from the sensors to a second communication unit 21 arranged on the ground. Furthermore, the system 19 comprises a processing unit 22 also installed on the ground and capable of processing the measurement data to determine the amount of carbon dioxide absorbed by the soil infiltrate. Depending on the application, the second communication unit and the processing unit 22 can form a single unit, wherein they are optionally directly connected to each other, or the system 19 can comprise a further communication unit. The system 19 can for example be used for remotely controlling the device 3 and / or for remotely analyzing the measurement data. The system 3 can also be used for positioning the device 3, for example for the purpose of maintaining or repairing the device 3.

[0139] List of reference numbers 1 soil infiltrate 2 soil 21 soil surface 3 device 4 solid 5 upstream wall 6 alkalinity storage layer 6a,b sub-layers of the alkalinity storage layer 7 measurement position 8 downstream wall 9 soil column 10 first reference section of the soil 11 downstream gap layer 12 upstream gap layer 13 tensiometer 14 pump 15 housing 16 detection wall 161 first side of the detection wall 162 second side of the detection wall 17 first sensor 17a,b plurality of first sensors 18 side wall 19 system 20 first communication unit 21 second communication unit 22 processing unit configured to be installed on the ground 23 maintenance door 24 power supply 25 sensor processing unit 26 first permeate flow guiding structure 27 dry compartment 28 wet compartment 29 second permeate flow guiding structure 30 second sensor

Claims

1. An apparatus (3) for determining the amount of carbon dioxide absorbed by soil permeate (1) during a measurement period, comprising: a. A housing (15) comprising a permeable upstream wall (5) and a permeable downstream wall (8), both of which define a permeable flow path; b. An alkalinity storage layer (6) arranged along the infiltration flow path between the upstream wall (5) and the downstream wall (8), wherein the alkalinity storage layer (6) is formed of a material having a plurality of acidic groups on its surface, such that when soil permeate (1) containing aqueous bicarbonate ions and / or aqueous carbonate ions permeates through the alkalinity storage layer (6), at least a portion of the acidic groups are deprotonated.

2. The apparatus (3) according to claim 1, wherein the material forming the alkalinity storage layer (6) is a material that changes its volume expansion when soil permeate (1) containing aqueous bicarbonate ions and / or aqueous carbonate ions permeates through the alkalinity storage layer (6).

3. The apparatus (3) according to claim 2, wherein the alkalinity storage layer (6) contacts a first side (161) of the detection wall (16) such that changes in volume expansion of the material forming the alkalinity storage layer (6) result in strain on the detection wall (16) and / or physical deformation of the detection wall (16).

4. The apparatus (3) according to claim 3, wherein the detection wall (16) is elastically deformable, preferably by the elastic outward protrusion of the detection wall (16) on a second side (162) opposite to the first side (161) of the detection wall (16), such that the change in volume expansion of the material forming the alkalinity storage layer (6) causes physical deformation of the detection wall (16).

5. The device (3) according to any one of claims 3-4, wherein the detection wall (16) has a lower bending stiffness than the sidewall of the housing (15).

6. The apparatus (3) according to any one of claims 2-5, further comprising a first sensor (17) for measuring changes in volume expansion of the material forming the alkalinity storage layer (6) during at least a portion of the measurement time period.

7. The apparatus (3) according to claim 6, wherein the first sensor (17) comprises a sensor for measuring strain on the detection wall (16) and / or physical deformation of the detection wall (16).

8. The apparatus (3) according to claim 6 or 7, wherein the first sensor (17) comprises a strain gauge interconnected to the detection wall and / or a piezoelectric sensor interconnected to the detection wall (16).

9. The apparatus (3) according to any one of the preceding claims, wherein the alkalinity storage layer (6) comprises a plurality of sublayers (6a, 6b) arranged sequentially to each other along the permeation flow path.

10. The apparatus (3) according to claim 9, comprising a plurality of first sensors (17a, 17b), wherein each sublayer (6a, 6b) is interconnected with a corresponding first sensor (17a, 17b) for measuring changes in volume expansion of the material forming the corresponding sublayer (6a, 6b) during at least a portion of a measurement time period.

11. The apparatus (3) according to any one of the preceding claims, wherein the plurality of acidic groups have a pKa of less than 6.35, preferably 2 to 6, more preferably 3 to 6.

12. The apparatus (3) according to any one of the preceding claims, wherein the plurality of acidic groups are carboxylic acid groups and / or sulfonic acid groups, preferably carboxylic acid groups.

13. The apparatus (3) according to any one of the preceding claims further includes a second sensor (30) interconnected with the alkalinity storage layer (6) and configured to measure the protonation state of acidic groups during at least a portion of a measurement time period.

14. The device (3) according to any one of the preceding claims, wherein the housing (15) further comprises a substantially impermeable sidewall (18) circumferentially surrounding the alkalinity storage layer (6).

15. The apparatus (3) according to any one of the preceding claims, wherein the alkalinity storage layer (6) has a water conductivity of 1 to 4000 cm / day, preferably 100 to 2000 cm / day, more preferably 1000 to 1500 cm / day.

16. The apparatus (3) according to any one of the preceding claims, wherein the alkalinity storage layer (6) comprises a buffer.

17. The apparatus (3) according to any one of the preceding claims further includes a pH detector configured to measure the pH and / or pH change of the alkalinity storage layer (6) during at least a portion of a measurement time period.

18. The apparatus (3) according to any one of the preceding claims, wherein the alkalinity storage layer (6) comprises a resin, preferably an ion exchange resin, wherein the resin is swellable and / or shrinkable when in contact with an aqueous solution having a pH higher than 7, preferably when in contact with an aqueous solution having a pH of 8 or higher, and more preferably when in contact with aqueous bicarbonate ions and / or aqueous carbonate ions.

19. The apparatus (3) according to any one of the preceding claims, further comprising a flow control unit configured to control the internal flow rate of soil permeate (1) permeating through the apparatus (3) such that the internal flow rate has a known or determinable flow rate ratio relative to the external flow rate of soil permeate (1) permeating through a first reference section (10) of soil (2) disposed outside the apparatus (3).

20. The apparatus (3) according to any one of the preceding claims further includes a downstream gap layer (11) arranged along a flow path downstream of the alkalinity storage layer (6) and having a higher hydraulic conductivity than the alkalinity storage layer (6) to minimize the backflow of soil permeate (1) from the downstream gap layer (11) to the alkalinity storage layer (6).

21. A system (19) for determining the amount of carbon dioxide absorbed by soil permeate (1), comprising: a. The apparatus (3) according to any one of the preceding claims, wherein the apparatus (3) is configured to be installed in underground soil (2) and further includes a first communication unit (20) configured to transmit underground measurement data measured during at least a portion of the measurement time period; b. A second communication unit (21), which is configured to be installed on the ground and configured to receive underground measurement data; c. Processing unit (22), which is configured to be installed on the ground and configured to determine the total alkalinity absorbed by the alkalinity storage layer (6) during the measurement period based on underground measurement data.

22. Use of the apparatus (3) according to any one of claims 1-20 or the system (19) according to claim 21 for determining the amount of carbon dioxide absorbed by soil permeate (1), preferably in the process of enhancing weathering.

23. A method for determining the amount of carbon dioxide absorbed by soil permeate (1), wherein the method comprises: a. Positioning the device (3), preferably the device according to any one of claims 1-20, at a measuring position (7) in the soil (2), such that the upstream wall (5) of the device (3) is arranged below the soil surface (21), wherein the alkalinity storage layer (6) of the device (3) is arranged vertically below the upstream wall (5), wherein the alkalinity storage layer (6) is formed of a material having a plurality of acidic groups on its surface; b. Allow the solid (4) to react with water and carbon dioxide during the measurement period to form soil permeate (1) that permeates through the soil (2) and through the alkalinity storage layer (6), thereby deprotonating at least a portion of the acidic groups of the material forming the alkalinity storage layer (6) during the measurement period; c. Determine the total alkalinity absorbed by the alkalinity storage layer (6) during at least a portion of the measurement time period; d. Based on the measured total alkalinity absorbed by the alkalinity storage layer (6), determine the total amount of carbon dioxide absorbed by the soil permeate (1) during the measurement period.

24. The method of claim 23, wherein step c) of determining the total alkalinity absorbed by the alkalinity storage layer (6) during at least a portion of the measurement time period comprises: ci) Determine the change in volume expansion of the material forming the alkalinity storage layer (6) during at least a portion of the measurement time period; and c.ii) Based on the change in volume expansion of the material forming the alkalinity storage layer (6) measured during at least a portion of the measurement time period, the total alkalinity absorbed by the alkalinity storage layer (6) during at least a portion of the measurement time period is determined.

25. The method according to claim 24, wherein the change in volume expansion of the material forming the alkalinity storage layer (6) is the swelling and / or shrinkage of the material forming the alkalinity storage layer (6) that occurs when soil permeate (1) formed by the reaction of solid (4) with water and carbon dioxide permeates through the alkalinity storage layer (6).

26. The method according to any one of claims 23-25, wherein the method further comprises controlling the internal flow rate of soil permeate (1) infiltrating through the device (3) during the measurement time period, such that the internal flow rate has a known or determinable flow rate ratio relative to the external flow rate of soil permeate (1) infiltrating through a first reference section (10) of soil (2) disposed outside the device (3).

27. The method of claim 26, wherein the step of controlling the internal flow includes controlling the vacuum pressure inside the device (3).

28. The method according to any one of the preceding claims, wherein the step of determining the total alkalinity absorbed by the alkalinity storage layer (6) during the measurement time period comprises: a. Measure the total interval alkalinity absorbed by the alkalinity storage layer (6) during the corresponding intervals within the measurement time period; and b. Based on the total interval alkalinity measured at multiple intervals, the total alkalinity absorbed by the alkalinity storage layer (6) during the measurement period is determined.

29. The method of claim 28, wherein the step of providing the determination of the total alkalinity absorbed by the alkalinity storage layer (6) during the measurement period is provided by summing the total interval alkalinity of all intervals that are determined to be positive total interval alkalinity, wherein optionally the total interval alkalinity of all intervals that are determined to be negative total interval alkalinity is discarded.

30. The method according to any one of claims 23-29, wherein the step of determining the total alkalinity absorbed by the alkalinity storage layer (6) comprises: a. Measure the total alkalinity absorbed by at least a portion of the plurality of sublayers (6a, 6b) of the alkalinity storage layer (6) arranged vertically stacked on top of each other; b. Based on the measured total alkalinity absorbed by the corresponding sublayers (6a, 6b), the total alkalinity absorbed by the alkalinity storage layer (6) is determined.

31. The method according to claim 30, wherein: a. If the measured total alkalinity absorbed by the corresponding sublayers (6a, 6b) decreases in the vertical direction from each sublayer (6a, 6b) to each downstream sublayer (6a, 6b), the total alkalinity absorbed by the alkalinity storage layer (6) is provided as the sum of the total alkalinity absorbed by all sublayers (6a, 6b); b. If the total alkalinity of at least one sublayer is lower than the total alkalinity of the downstream sublayer arranged vertically below the adjacent sublayer, the total alkalinity of the at least one sublayer is not included in the determination of the total alkalinity absorbed by the alkalinity storage layer (6).

32. The method according to any one of claims 23-31, wherein the device (3) further comprises a downstream gap layer (11) disposed downstream of the alkalinity storage layer (6) and having a higher hydraulic conductivity than the alkalinity storage layer (6) to minimize the backflow of soil permeate (1) from the downstream gap layer (11) to the alkalinity storage layer (6).

33. The method according to any one of claims 23-32, wherein the mineral (4) comprises a silicate mineral (4).

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