Enhanced weathering carbon dioxide removal quantification method and apparatus

Abstract

A method for quantifying carbon dioxide removal when performing enhance weathering operations. Measurements are enabled by taking soil cores 810, placing the core sample into a water bath, 820, leave

Description

Field The present invention relates to methods of quantifying carbon dioxide removal when performing enhanced weathering operations. More particularly, the present invention relates to enabling measurements to be taken from soil cores of enhanced weathering products by extracting pore soil water. Background Enhanced weathering is the process of spreading suitable crushed silicate rock materials over suitable land, such as farmland. Suitable rock materials include rock such as basalt, which naturally reacts with dissolved carbon dioxide in the form of carbonic acid to remove the carbon dioxide from the environment. By crushing the rock, the crushed rock has a larger surface area per particle which speeds up the process of capturing carbon dioxide by increasing the reaction surface area. By spreading the rock over, for example, farmland, carbon dioxide can be captured over a large land surface. During enhanced weathering, it is important to measure the properties of the enhanced weathering reaction in order to measure the amount of carbon dioxide captured in the soil, rivers and eventually oceans. This data can be used to compare against modelled carbon capture, verify carbon credits, or plan further enhanced weathering based on weathering performance. To measure enhanced weathering, one of the measurement options is to extract pore water using a tool called a macro rhyzon in order to determine the level of carbon capture from the sample or samples is obtained. However, when the soil has a low moisture content, it is difficult to extract enough moisture from the soil to get reliable data. Summary of Invention Aspects and / or embodiments seek to provide a method to extract sufficient pore water samples from soil, even when the soil has a low moisture content, in order to perform measurements on the pore water, for example to verify or measure enhanced weathering for the purpose of the quantification of carbon dioxide removal. According to a first aspect, there is provided method of obtaining pore water samples from a soil sample (800) comprising: placing the soil sample in a bath of water (820); removing the soil sample from the bath of water (830); applying pressure to the soil sample to extract at least some water content from the soil sample (850). By allowing the soil sample to be placed in water, the soil sample can saturate with water and this can allow the subsequent removal of both the added water and the original water content for subsequent testing. This can allow the testing of water in a soil sample containing substantially too low a moisture content to provide sufficient water for normal pore water testing. Optionally, the soil sample is contained in a sample tube. Optionally, the sample tube is substantially made from metal and / or is substantially cylindrical. Optionally, the sample tube comprises one or more caps, the one or more caps operable to seal the contents of the sample tube. The soil sample can be contained in a variety of configurations of sample apparatus, but can typically be obtained using a configuration of sample apparatus that is operable to work with a standard centrifuge and / or standard configuration of mechanical pressure apparatus. Optionally, the bath of water comprises a bath of sterilised distilled water. In other embodiments, artificial rainwater can be used. Using sterilised distilled water and / or artificial rainwater can allow the extracted water content to retain substantially all of the properties desired to be measured. Optionally, the step of placing the soil sample in a bath of water comprising placing the soil sample in the bath of water for substantially 24 hours and / or at substantially 2 to 4 degrees Celsius. Placing the soil sample in a bath of water under substantially these conditions can allow the soil sample to saturate with the water contained in the bath and / or substantially not change the properties of the soil sample and / or its water content. Optionally, the step of removing the soil sample from the bath of water comprising removing the soil sample from the bath of water for sufficient duration to allow free drainage. Removing the soil sample from the bath of water can allow only water that has been absorbed by the soil sample to remain prior to further step of the process being performed. Optionally, the step of applying pressure to the soil sample comprises placing the soil sample in a centrifuge. Placing the soil sample in a centrifuge can remove the moisture content of the soil substantially quickly, and / or causes water molecules being removed from the soil sample during the centrifuge operation to pull neighbouring water molecules out of the soil sample. Optionally, the centrifuge spins the soil sample for substantially 30 minutes and / or at substantially 1,000 revolutions per minute. Using this configuration of centrifuge equipment can allow sufficient water to be removed from the soil sample to allow subsequent tests to be performed on a substantially sufficient sample size. Optionally, the method further comprises the step of filtering the extracted water content. Optionally, the step of filtering is performed for substantially 5 to 10 minutes. By filtering the water, debris such as soil can be removed which might otherwise impact the measurements / analysis performed on the extracted water. Brief Description of Drawings Embodiments will now be described, by way of example only and with reference to the accompanying drawings having I ike-reference numerals, in which: Figure 1 shows an example enhanced weathering process; Figure 2 shows an example of a soil core sample container; Figure 3 shows an example of the use of the soil core sample container, prior to insertion into the soil to be sampled; Figure 4 shows an example of the use of the soil core sample container to insert into the soil to be sampled; Figure 5 shows an example of the use of the soil core sample container being removed from the soil to be sampled; Figure 6 shows an example of the use of the soil core sample container to contain the soil to be sampled; Figure 7 shows an example of the use of the soil core sample container being secured for transport with the soil sample inside; and Figure 8 shows an embodiment of the enhanced soil core moisture process. Specific Description Referring to Figure 1, an example of an enhanced weathering process 100 will now be described. Enhanced weathering is performed by adding crushed rock 130 to farmland 140. In this described embodiment, the crushed rock 130 is added using farm machinery 120 such as a tractor with a trailer containing the crushed rock 130, where the trailer is configured to disperse the crushed rock 130 in a predetermined dispersal rate over substantially all of the surface of the farmland 140 as the farm machinery 120 travels along the farmland 140, typically travelling along parallel lines back and forth along the farmland 140. Not all of the land needs to be subject to enhanced weathering, so in this embodiment farmland 140 undergoes the enhanced weathering process 100 but non-weathered land 110 does not have any crushed rock 130 spread over its surface. In this embodiment, the properties of the farmland 140 that is to be subject to the enhanced weathering process 100 are determined in advance based on a combination of data for the area in which the farmland 140 is located along with data collected from the farmland 140. This data includes expected rainfall, pH, soil composition. Other data that is used as part of the process 100 is data pertaining to the crushed rock 130, including geochemical properties of the crushed rock and the range of surface area of the rock particles. Using this data, the amount of crushed rock 130 to spread over the farmland 140 and the density of spread / amount to be spread over the farmland 140 is calculated in advance of the spreading operation by the farm machinery 120. In other embodiments, different data can be obtained in advance of the spreading operation. In other embodiments, a spreading plan can comprise different arrangements for different parts of the farmland 140, for example differing amounts of rock to be spread on different portions of the farmland 140. In other embodiments, different equipment can be used to spread the crushed rock 130. In other embodiments, multiple spreading operations may be performed at one or more time intervals. In other embodiments, sensors can be used to monitor the properties of the farmland 140, before and / or after the one or more spreading operations being performed. Following the enhanced weathering operation 100, carbon dioxide is absorbed from the atmosphere above the farmland 140 by a chemical reaction between the dissolved carbon dioxide and the crushed rock 130 spread over the surface of the farmland 140. This captures and sequesters carbon dioxide from the atmosphere into the soil over substantially the entire area that has been subject to enhanced weathering operations 100. Depending on the parameters that have been calculated for the rock spreading operation(s), the rate of carbon dioxide capture depends on the amount and properties of the crushed rock 130 that has been spread over the farmland 140 and a prediction for this carbon dioxide capture will be determined from the calculated parameters for the rock spreading operation(s). Following the enhanced weathering operation 100, one of the measurements that needs to be performed to verify the amount of carbon captured is to measure the properties of the water in the soil, specifically the pore water. Pore water measurements can be key to understanding the soil chemistry and therefore how much carbon dioxide has been removed from the atmosphere. Enhanced weathering performance can depend on the pore water leaving the soil via the normal channels (e.g. streams and rivers) and reaching the ocean. Therefore, operators of enhanced weathering processes typically measure the contents of water in fields undergoing enhanced weathering to demonstrate bicarbonate and cation content in the pore water, which then leaves the soil and in time enters the ocean. Should the soil contain too little moisture, for example in circumstances where there has been little rainfall (e.g. when there has been a drought for a number of months), it becomes difficult to extract enough water from a soil sample to conduct normal tests of the pore water. If this is the case then the following process can be used to obtain sufficient water from soil that contains too little moisture. Pore water samples also should be analysed within around 36 hours of taking the sample, as the partial pressure of carbon dioxide in soil is different to that in air, so over time there is outgassing and degradation of the data (e.g. the bicarbonates in the soil sample will typically degrade over time as the pressure equilibrium moves from that of soil to that of air) that can be obtained from the pore water if tests aren’t performed promptly. Simply applying a large degree of pressure to the soil samples may not be possible is the moisture content is too low, as there is a limit to the amount of mechanical suction / pressure that is possible and depending on the type of soil it becomes impossible to extract sufficient water once the moisture levels drop below a certain level (this level varies by soil composition). Some methods of suction / pressure can extract sufficient water from soil samples but take too long, and after 36 hours from taking the soil sample the water extracted doesn’t provide a representative sample for analysis. Referring to Figure 2, an example soil core sample container 200 will now be described. The sample tube 220 is a hollow metal cylinder, which has two caps or lids, a top lid 210 and a bottom lid 230. The top and bottom lids 210, 230 are designed to fit on to the open ends of the tube 220 to secure and seal the sample soil contained within the sample tube 220. In this embodiment the caps 210, 230 fit to the ends of the tube 220 by an interference fit. In other embodiments, the caps 210, 230 can use a screw thread to fit to the tube 220. In other embodiments, other fixing mechanisms can be used to secure the lids 210, 230 to the tube 220. In this embodiment, each cylinder has a 5cm diameter and is 5cm deep. Typically, in this embodiment, multiple samples will be taken each with separate soil core sample containers, commensurate to the area of land being sampled. Referring to Figure 3, an example of use 300 of the soil core container of Figure 2 will now be described. A sample tube 310 (as described above in relation to Figure 2) is shown in this embodiment without caps. It is positioned above the surface of the soil 320. The intention is to sample a core of soil by inserting the sample tube 310 into the soil surface 320 to obtain a core of soil within the sample tube 310. Referring to Figure 4, an example of soil sampling 400 using the soil core container of Figure 2 will now be described. The sample tube 410 is inserted 440 into the soil, penetrating the soil surface 420 and thereby causing a sample of soil 430 to enter into the sample tube 410. In this embodiment, the tube 410 is hammered into the soil. Referring to Figure 5, an example of soil sample removal 500 using the soil core container of Figure 2 will now be described. The sample tube 510 is removed 540 from the soil surface 520, leaving a hole 550 and with the soil sample 530 contained within the sample tube 510. The soil sample 530 typically stays within the sample tube 510 when it is removed from the ground. It is typically very important to keep the soil core as a solid undisturbed soil sample hence it is kept intact within the cylinder 510. Referring to Figure 6, an example of securing the soil 600 within the soil core container of Figure 2 will now be described. The sample tube 610 containing the soil sample 630 then has the two lids 620, 640 placed at either open end of the cylinder 610 containing the soil sample 630. The top lid 620 is fit over one end of the sample tube 610 using an interference fit. The bottom lid 640 is fit over the other end of the sample tube 610 using an interference fit. The lids 620, 640 prevent the soil or any moisture from leaving the interior of the sample tube 610. In other embodiments, other fastening mechanisms can be used to fasten the lids 620, 640 to the tube 610. Referring to Figure 7, an example of readying the soil sample for transport 700 using the soil core container of Figure 2 will now be described. The sample tube 710 is shown with both lids 720, 740 securely fastened over either open end of the cylinder 710 containing the soil sample 730. The soil sample 730 is able to be transported securely within the sample tube 710, for example to a laboratory for testing the contents of the tube 710. Referring to Figure 8, an embodiment of the enhanced soil core moisture process 800 will now be described. In a first step 810, the soil sample in the sample tube is received 810. Typically this will be in a laboratory-setting with equipment to analyse the contents of the sample tube. In a second step 820, the soil sample tube has at least one lid removed and the open side of the tube is placed in a bath of sterilised distilled water. In this embodiment, each sample is saturated in 60ml of sterilised distilled water. In this embodiment, 60ml of sterilised distilled water should be sufficient for the soil sample size (using a 5cm diameter and 5cm deep cylinder) not to dilute the “signal” being analysed when testing the water extracted at the end of the process of this embodiment. In this embodiment, de-ionised water or very pure water is not used to prevent the soil leaching some of its contents into the bath of water (which will alter the subsequent analysis data detrimentally). In some embodiments, artificial rainwater can be used. In a third step 830, the sample tube is left for 24 hours at 2-4 degrees Celsius to saturate with the sterilised distilled water. In a fourth step 840, the sample tube is removed from the bath of water in order to allow free drainage of any water that hasn’t soaked into the soil sample in the tube. In a fifth step 850, the sample is placed into a centrifuge and spun for thirty minutes at 1,000 revolutions per minute in order to extract the water from the soil sample. The water is collected by the equipment. Typically about 20-30ml will be collected from each soil sample. In a sixth step 860, the water collected by the centrifuge is filtered for five to ten minutes. This filtered water can then be processed as would a normal pore water sample where the soil sample contains sufficient moisture. The filtration aims to remove for example small pieces of soil. In some embodiments, the filtration step could occur earlier by for example placing filter paper at at least one (or both) sides of the cylinder containing the soil sample. Measurements in this embodiment are then taken of alkalinity, pH and EC. In some embodiments, any or any combination of the following measurements as follows can betaken: pH using a benchtop pH meter; EC using a benchtop EC meter; alkalinity using titration using 0.1M HCL; cations using ICP-AES; anions using IC. In some embodiments, a moisture probe can be used in the soil to be sample prior to take soil core samples and the data from the moisture probe can be used to determine how much water should be contained in the water bath in order to determine how much the pore water sample is diluted by the saturation step in process 800. In some embodiments, in place of a centrifuge, a mechanical pressure device can be used such as a hydraulic press. Any system feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. Any feature in one aspect may be applied to other aspects, in any appropriate combination. In particular, method aspects may be applied to system aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects can be implemented and / or supplied and / or used independently.

Claims

1. A method of obtaining pore water samples from a soil sample (800) comprising: placing the soil sample in a bath of water (820);removing the soil sample from the bath of water (830);applying pressure to the soil sample to extract at least some water content from the soil sample (850).

2. The method of any preceding claim, wherein the soil sample is contained in a sample tube.

3. The method of claim 2 wherein the sample tube is substantially made from metal and / or is substantially cylindrical.

4. The method of either claims 2 or 3 wherein the sample tube comprises one or more caps, the one or more caps operable to seal the contents of the sample tube.

5. The method of any preceding claim, wherein the bath of water comprises a bath of sterilised distilled water.

6. The method of any preceding claim, wherein the step of placing the soil sample in a bath of water comprising placing the soil sample in the bath of water for substantially 24 hours and / or at substantially 2 to 4 degrees Celsius.

7. The method of any preceding claim, wherein the step of removing the soil sample from the bath of water comprising removing the soil sample from the bath of water for sufficient duration to allow free drainage.

8. The method of any preceding claim, wherein the step of applying pressure to the soil sample comprises placing the soil sample in a centrifuge.

9. The method of claim 8 wherein the centrifuge spins the soil sample for substantially 30 minutes and / or at substantially 1,000 revolutions per minute.

10. The method of any preceding claim further comprising the step of filtering the extracted water content.

11. The method of claim 10 wherein the step of filtering is performed for substantially 5 to10 minutes.

Images