Method for quantifying the microplastic content in a biomass sample or a sample derived from biomass

Abstract

The invention relates to a method and system for quantifying the microplastic content in a biomass or biomass-derived sample, based on an organic matter stability index for the sample. The invention implements a step of heating the sample and comparing two indices (R and R0) to deduce the quantity of microplastics, the R index being obtained from the sample heating and the R0 index being obtained from the organic matter stability index for the sample. Figure 1A to be published.

Description

Title of the invention: Method for quantifying the microplastic content in a sample of biomass or derived from biomass technical field

[0001] The present invention relates to the fields of soil science, environmental geosciences, and agronomy and agriculture. More specifically, the present invention relates to the quantification of microplastics contained in or derived from a biomass sample (including organic waste products from physical and biological treatments or soil-WW mixtures).

[0002] The present invention finds particular application for the evaluation of conformity with current standards relating to spreading products in agriculture.

[0003] In an economic context of increased food and environmental yields, particularly aimed at reducing the use of nitrogen fertilizers, the spreading of organic matter (raw or processed organic matter) in the field is of major agronomic interest for assessing soil quality. Indeed, spreading organic matter on the soil promotes the return of nutrients and organic matter to the soil, thereby reducing the need for mineral fertilizers and maintaining soil carbon (C) stocks. Organic products thus have a dual agronomic value: 1) fertilizing (providing mineral and / or organic nutrients) and 2) improving (providing organic matter). These organic amendments, even with the same organic matter content, can exhibit very different behaviors, especially since they are now numerous and increasingly diverse.

[0004] However, bio-based products (crop residues, organic waste of animal, plant, or urban origin) or organic waste products (OWP) from physical and biological treatments (composts, digestates, sludge, etc.) are recognized as a source of microplastics (MP) introduction into the environment following their application to agricultural soils. To date, MPs are not detected during the production processes of these products. Thus, the application of products originating from biomass leads to soil contamination by these elements, the impact of which on life and the resulting biological functioning of the soil remains poorly understood. However, current and future regulations in France and Europe aim to significantly limit future sources of plastic introduction. in the environment. Thus, the quantification of microplastics through the addition of bio-based products to the soil constitutes a societal challenge. Previous technique

[0005] The following documents will be cited during the description:

[0006] Vincent Ducasse, Françoise Watteau, Isabelle Kowalewski, Herman Ravelojaona, Yvan Capowiez, Joséphine Peigné, Amending potential of vermicompost, compost and digestate from urban biowaste: evaluation using biochemical, Rock-Eval® thermal analyses and transmission electronic microscopy, Bioresource Technology Reports, 2023, https: / / doi.org / 10.1016 / j.biteb.2023.101405

[0007] Sebag D., Verrecchia EP, Cécillon L., Adatte T., Albrecht R., Aubert M., Bureau F., Cailleau G., Copard Y., Decaens T., Disnar J.-R., Hetényi M., Nyilas T., Trombino L., 2016. Dynamics of soil organic matter based on new Rock-Eval indices. Geoderma 284, 185-203, https: / / doi.Org / 10.1016 / j.geoderma.2016.08.025.

[0008] Sebag, D., Verrecchia, E.P., Adatte, T., Aubert, M., Cailleau, G., Decaëns, T., Kowalewski, L, Trap, J., Bureau, F, Hedde, M. (2022). Size fractions of organic matter pools influence their stability: Application of the Rock-Eval® analysis to beech forest soils. Pedosphere Vol. 32(4), pp. 565-575, https: / / doi.org / 10.1016 / S 1002-0160(21)60050-4.

[0009] Among the methods commonly used to quantify (by number or mass) or even identify isolated microplastics, we know of spectroscopic methods (Infrared or Raman, for example), Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared microspectroscopy (pFTIR, for "micro Fourier Transform Interferometer"), and pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS). However, since these methods do not allow for the separation of organic matter from plastic particles, the organic matter must first be removed from the sample to be analyzed, or the microplastics must be highly concentrated beforehand.More specifically, it is generally necessary to remove most of the sample matrix (mineral and organic), preferably by isolating the microplastic particles from the matrix and removing any substances adhering to them. For inhomogeneous solid samples such as soils, isolating microplastics is challenging and becomes even more so as the grain size of the soil matrix and the size of the microplastic particles decrease. Isolation methods (extraction-purification) require numerous extractions using solvents and separation methods (filtration, sieving, density separation, etc.) before quantification (by number or mass) is possible. It is even possible to identify isolated microplastics using spectroscopic (IR or Raman, for example), microscopic, and / or thermal methods (DSC, TGA, Py-GC-MS, etc.). Isolation methods are solvent-intensive, laborious, time-consuming, and cumbersome to implement. After this over-concentration, quantification methods remain more or less effective and are not standardized.

[0010] Patent application WO 2022 / 243080 A1 is also known, which relates to a thermal analysis for characterizing the plastic content in samples of a porous medium such as sand. More specifically, this method is based on measurements of the quantities of hydrocarbon compounds (HC), carbon monoxide (CO), and / or carbon dioxide (CO2) released over time by a sample subjected to a heating sequence in an inert atmosphere followed by a heating sequence in an oxidizing atmosphere, applied to solid samples. A database of reference samples, previously prepared from different mineral matrices and several types of polymers (e.g., PE, PP, PE100, PA6, PAU, PFA, and PET), distributed in predetermined concentrations, is established beforehand.Parameters derived from the thermal analysis results for the sample under analysis are compared to those from the reference sample database for the identification and differentiation of polymer families. This approach therefore requires that the type(s) of microplastic(s) present in the sample be included in the reference sample database and involves a step to identify these different polymer types. Specifically, the identification of the microplastic type can be performed by identifying the peak temperatures in the measured HC, CO, and / or CO2 curves and by cross-referencing them with the peak temperatures of the corresponding curves measured for the plurality of reference samples. These temperatures may vary depending on the additives present in the microplastics and their aging process within the biomass.Quantification for each type of polymer is then performed by integrating the areas of the identified peaks. However, the quantification method described in this document can be difficult to apply when organic matter is present in the sample (depending on the organic matter to microplastics ratio), as it is then difficult to distinguish the peaks associated with microplastics from those associated with organic matter. Deconvolution, using reference peaks for each identified polymer, is then necessary, but this technique may have limitations in terms of accuracy. Thus, this method does not appear suitable for the accurate quantification of polymers in a non-porous material composed almost exclusively of organic matter, such as biomass or a biomass product. Given that microplastics are introduced into soils by... pathways such as biomass origin or processed is the most important and that these microplastics are not detected today, this deconvolution measurement method is a fast way to reduce the penetration of plastics and microplastics into the environment.

[0011] The present invention aims to overcome the drawbacks of the prior art. In particular, the present invention allows, from a thermal analysis comprising a single heating sequence under an inert atmosphere (pyrolysis), a rapid, simple, and reliable quantification of microplastics in a biomass sample or a biomass product. Furthermore, the present invention does not require any prior pretreatment and requires only a sample of a few mg. Summary of the invention

[0012] The invention relates to a method for quantifying the microplastic content in a sample of biomass or derived from biomass, based on a predefined organic matter stability index for said sample. It comprises at least the following steps:

[0013] A) said sample is heated in an inert atmosphere according to a predefined temperature sequence of which an initial temperature (T0) is between 100 and 300 °C, and a final temperature (TF) is between 650 and 800 °C, said temperature sequence comprising at least a thermal gradient between 1°C / min and 50°C / min, and at least a quantity of HC released during said heating sequence in an inert atmosphere is continuously measured;

[0014] B) a first indicator R is determined, representative of the thermal stability of the organic carbon present in the sample, from said quantity of HC measured continuously and according to a formula of the type:

[0015] R = ((A3 +A4 + A5) / 100)(2)

[0016] Where A3, A4, and A5 correspond to an organic carbon content released in the form of HC during said heating sequence under inert atmosphere in a temperature range of respectively between 400 and 460°C, between 460-520°C and between 520-650°C;

[0017] C) A second indicator R0 is determined, representative of the thermal stability of the organic carbon present in the sample, according to a formula of the type:

[0018] R0 = (ISMO - b)la (3)

[0019] where ISMO is said organic matter stability index for said sample, and a and b are predetermined coefficients;

[0020] D) the quantity of microplastics QMP in the sample is determined according to a formula of the type:

[0021] q MP = f^c(T)dT

[0022] T1 being preferably between 150°C and 300°C and most preferably 200°C, and T2 being preferably between 600°C and 700°C and most preferably 650°, m the mass of said sample, C(T) the curve of the evolution of the organic compounds released by the sample as a function of the temperature during the heating of the sample.

[0023] According to one embodiment, the quantity of carbon in the MP sample is determined by multiplying the quantity QMP must be multiplied by a stoichiometric coefficient of the form 100 / x with x the percentage of carbon of the microplastic considered.

[0024] In accordance with an implementation, said organic matter stability index is determined for said sample by means of a biochemical fractionation method, preferably according to AFNOR standard FD U44-162, and a method for measuring carbon mineralization at 3 days, preferably according to standard FD U44-163 (02 / 2018).

[0025] According to one aspect, said organic matter stability index for said sample is determined by means of the following formula: ISMO = 445 + 0.5*SOL-0.2*CEL+ 0.7*LIC - 2.3*Ct3, with SOL the soluble fraction of said sample, CEL a cellulose equivalent of said sample, LIC a lignin and cutin equivalent of said sample and Ct3 the content of mineralized exogenous organic carbon after three days of controlled incubation.

[0026] Advantageously, said temperature sequence under inert atmosphere includes a first isothermal plateau at the initial temperature (T0), followed by a predetermined thermal gradient so as to raise the temperature of the sample up to the final temperature (TF).

[0027] According to one embodiment, said temperature sequence may include a second isothermal plateau at the final temperature (TF).

[0028] According to one embodiment, said temperature sequence includes at least one isothermal plateau at an intermediate temperature between said initial temperature (T0) and the final temperature (TF).

[0029] According to one embodiment, the A3, A4 and A5 contents are determined according to the following formulas:

[0030] A3=A / 460c(T)dT 100311 A4 = ^®C(T)dT 100321 A5 = ∫°C(T)dT

[0033] With m the mass of said sample, C(T) a curve of the evolution of hydrocarbon released by the sample as a function of temperature during heating of the sample.

[0034] Advantageously, the coefficients a and b are predetermined from a plurality of reference samples, for which said organic matter stability index for said sample is predetermined.

[0035] According to one embodiment, the coefficient a is between 100 and 150, and preferably equals 123, and the coefficient b is between 10 and 50 and preferably equals 22.

[0036] Furthermore, the invention relates to a system for quantifying the microplastic content in a sample of biomass or derived from biomass for the implementation of the process according to one of the preceding characteristics, comprising a pyrolysis furnace in an inert atmosphere for carrying out said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for determining said first indicator R representing the thermal stability of the organic carbon present in the sample, said second indicator R0 representing the thermal stability of the organic carbon present in the sample as well as the quantity of microplastics in said sample. List of figures [Fig AI]

[0037] Figure 1A schematically illustrates an example of implementing the temperature sequence under an inert atmosphere of the process according to the invention. [Fig. 1B]

[0038] Fig. 1B schematically illustrates another example of implementation of the temperature sequence under inert atmosphere of the process according to the invention. [Fig 2]

[0039] Figure 2 illustrates the values ​​of a first thermal stability indicator. according to the invention as a function of a predefined ISMO parameter for a plurality of biomass samples of different types, as well as a linear correspondence law representing the evolution of the ISMO parameter as a function of a second thermal stability indicator according to the invention. [Fig 3A] [Fig 3B] [Fig 3C]

[0040] Figures 3A, 3B and 3C present, in the form of a histogram, the percentage of microplastics contained in three different types of composted biomass samples taken over time. Description of the implementation methods

[0041] The invention relates to a method for quantifying microplastics contained in a sample of biomass or derived from biomass (including organic waste products from physical and biological treatments or soil and PRO mixtures).

[0042] The term “biomass” means any mass of living or recently living matter (animal, plant, terrestrial, aquatic) existing in equilibrium on a given surface of the Earth. This may include, but is not limited to, plants, wood, agricultural and organic biowaste, algae, etc.

[0043] The term "Organic Residual Products (ORP)" refers to all organic waste and by-products resulting from human activities such as agriculture, food processing, and household waste. These ORPs, organic products derived from biomass, can be transformed by various processes (biological, thermal, etc.) for the purpose of their recovery. Products derived from biomass and transformed include compost, vermicompost, digestate, biochar, etc.

[0044] By microplastics, we mean any particle comprising one or more polymers and being less than 5 mm in size.

[0045] The process according to the invention requires having at least one sample of biomass or a product derived from biomass to be analyzed.

[0046] Advantageously, the sample can be sieved using a sieve with 2 mm diameter orifices, dried at a temperature below 40°C, and then ground to obtain fragments with dimensions less than 200 µm. Furthermore, it is not necessary to pretreat the sample (in particular, no decarbonation, purification, or extraction), especially with solvents. The sample can have a mass between 1 and 100 mg. Indeed, the process according to the invention, particularly when implemented using the ROCK-EVAL® device (IFP Energies nouvelles, France) described below, does not require a large sample mass due to the sensitivity of the detectors.

[0047] The process according to the invention can advantageously, but not exclusively, be implemented using the ROCK-EVAL® device (IFP Energies nouvelles, France), as described in patents FR 2227797 (US 3953171) and FR 2472754 (US 4352673). Indeed, the ROCK-EVAL® device comprises at least:

[0048] - a pyrolysis oven in an inert atmosphere,

[0049] - means for measuring hydrocarbon compounds (HC), for example under the form of a flame ionization detector (FID).

[0050] The process can alternatively be implemented using any furnace allowing heating in an inert atmosphere, cooperating with one or more devices for measuring hydrocarbon compounds.

[0051] The process according to the invention requires a predefined value of the Index of Recalcitrant Organic Carbon (IROC). ISMO is a well-known indicator in the fields of agronomy and agriculture. It describes the capacity of any biomass product to contribute to the stable carbon pool. of soil organic matter. ISMO, expressed as a percentage of organic matter (percentage of stable organic matter relative to its total organic matter content), also takes into account the 3-day carbon mineralization kinetics. This is referred to as the "ISMO parameter" hereafter.

[0052] According to one embodiment of the invention, the ISMO parameter is determined by means of implementing at least one biochemical fractionation method, preferably according to AFNOR standard FD U44-162, and one method for measuring carbon mineralization at 3 days, preferably according to standard FD U44-163 (02 / 2018).

[0053] According to one embodiment of the invention, in a preliminary step of the process according to the invention, the ISMO parameter can be determined as follows: from an additional sample of the biomass or biomass product to be analyzed, the following substeps are applied: - drying at a temperature of 38°C of the additional sample and grinding to 1 mm of the dried additional sample; - Sequential extraction and quantification of the different biochemical fractions of the dried and ground additional sample, comprising a soluble fraction, a hemicellulose fraction, a cellulose fraction, and a lignin and cutin fraction. This fractionation, derived from the "Van Soest fractionation," allows the separation of at least four organic matter fractions whose sizes are determined by weight difference and then expressed as a percentage of total organic matter or as a percentage of total organic carbon in the exogenous organic matter. The organic matter is thus divided into several functional fractions, each with specific chemical and biological properties. - determination of mineralized carbon at 3 days, by means of at least one measurement of the CO2 release from the dried and ground sample.

[0054] According to one embodiment of the invention, the ISMO parameter can be determined according to the following formula:

[0055] ISMO (in g.kg1 MOE) = 445 + 0.5*SOL(%MO) - 0.2*CEL(%MO) + 0.7*LIC (%MO) - 2.3*Ct3 (%Corg) (1)

[0056] Where MOE corresponds to exogenous organic matter (in other words the mass of the biomass sample), SOL corresponds to the soluble fraction (in g.kg-lEOM), CEL corresponds to a cellulose equivalent (in g.kg 'EOM), LIC corresponds to a lignin+cutin equivalent (in g.kg 'EOM) and Ct3 corresponds to the content of exogenous organic carbon (EOC) (in gC kg 'EOC) mineralized after 3 days of controlled incubation.

[0057] This indicator, described in (Lashermes et al., 2009), results from a statistical correlation established between biochemical fractions and residual carbon levels determined by extrapolation of mineralization kinetics carried out under controlled conditions.

[0058] The method according to the invention comprises at least the following steps:

[0059] 1) Heating sequence under an inert atmosphere (pyrolysis)

[0060] 2) Determination of a first indicator of the thermal stability of carbon organic of the sample based on the amount of HC measured

[0061] 3) Determination of a second indicator of the thermal stability of carbon organic matter of the sample based on the predetermined ISMO parameter

[0062] 4) Quantification of microplastics present in the sample

[0063] The steps of the process according to the invention are described below.

[0064] 1) Heating sequence under an inert atmosphere (pyrolysis)

[0065] During this step, the sample is heated under an inert atmosphere (as by (for example, under a flow of nitrogen, argon, or helium) according to a temperature sequence in which the initial temperature (hereafter denoted T0) is between 100 and 300°C and preferably 200°C, and the final temperature (hereafter denoted TF) is between 650 and 800°C and preferably 650°C. Furthermore, the temperature sequence according to the invention includes at least one thermal gradient between 1°C / min and 50°C / min. In addition, according to the invention, at least a certain quantity of HC released during heating in an inert atmosphere is continuously measured.

[0066] The initial temperature of the process according to the invention allows the release of the most labile organic compounds (having a cracking temperature below 400°C) in a dissociated manner from the more resistant or even refractory organic compounds (having a cracking temperature below 400°C), which are of interest for the process according to the invention as will be described below.

[0067] The final temperature of the process according to the invention is sufficient for the release of highly stable pyrolisable organic compounds to be complete.

[0068] According to one embodiment of the invention, the temperature sequence under an inert atmosphere may include a first isothermal plateau at the initial temperature T0, optionally followed by a predetermined thermal gradient to raise the sample temperature to the final temperature TF. Figure 1A schematically illustrates the evolution of the temperature T as a function of time t in such a temperature sequence, exhibiting an isothermal plateau at temperature T0, followed by a thermal gradient until reaching temperature TF.

[0069] Advantageously, the temperature sequence under an inert atmosphere may include a second isothermal plateau, optionally in addition to the first isothermal plateau, at the final temperature TF. This allows the following to be continued, if necessary: Cracking of compounds having a cracking temperature close to the final temperature TF of the temperature sequence under an inert atmosphere according to the invention. Figure 1B schematically illustrates the evolution of the temperature T as a function of time t of a temperature sequence, exhibiting two isothermal plateaus, at temperatures T0 and TF as defined above, and linked by a thermal gradient.

[0070] According to one embodiment of the invention, the isothermal plateau(s) of the temperature sequence under an inert atmosphere may have a predetermined non-zero duration (for example, greater than half a minute), preferably between 1 and 5 minutes, and most preferably 3 minutes. Such durations allow the cracking of compounds having a cracking temperature close to the temperature of the isothermal plateau to be considered complete. According to the embodiment of the invention in which the temperature sequence under an inert atmosphere comprises several isothermal plateaus, and in particular two isothermal plateaus at temperatures T0 and TF, the duration of one isothermal plateau may differ from the duration of the other isothermal plateau(s).

[0071] Advantageously, the temperature sequence of the inert atmosphere heating may further include one or more intermediate isothermal plateaus at temperatures between the initial and final temperatures of the inert atmosphere heating sequence. According to one embodiment of the invention, the inert atmosphere heating temperature sequence may include an intermediate isothermal plateau at a temperature between 380 and 420 °C, and preferably 400 °C. This isothermal plateau can allow for better separation, in a curve representing the temperature evolution of the quantity of HC released during inert atmosphere heating, of the thermal classes associated with parameters A3, A4, and A5, which will be described below, and thus improve the accuracy of the process according to the invention.

[0072] The intermediate isothermal plateau(s) may have a predetermined non-zero duration (for example, greater than half a minute), preferably between 1 and 5 minutes, and most preferably 3 minutes. Such durations are sufficient to allow the dissociation of peaks associated with the different classes of organic compounds. According to this embodiment of the invention, the temperature sequence of heating under an inert atmosphere may include a number of thermal gradients NG defined by NG = NII+1 where NII is the number of intermediate isothermal plateaus in the temperature sequence. Thus, the intermediate isothermal plateau(s) are linked to each other by thermal gradients, and the intermediate isothermal plateau at the lowest temperature (respectively the higher) is also related by a thermal gradient to the initial temperature (respectively the final temperature) of the temperature sequence.

[0073] According to one embodiment of the invention, the thermal gradient(s) of the temperature sequence under an inert atmosphere can be between 1°C / min and 50°C / min, preferably between 10°C and 35°C / min, and most preferably 25°C / min. Such values ​​represent a compromise that allows for the thermal cracking of organic compounds while limiting the implementation time of the process.

[0074] According to the invention, a representative quantity of hydrocarbon compounds (HC) contained in an effluent resulting from said heating is continuously measured (i.e., continuously over time). In other words, during this sequence, the representative quantity of HC released by the sample through thermal cracking of organic matter and thermal decomposition of microplastics can be continuously measured. The measurement of the representative quantity of hydrocarbon compounds can be carried out using a flame ionization detector (FID). It should be noted that such sensors measure an HC flux and provide values ​​measured in millivolts (mV). Conventionally, the quantity of HC can be determined by calculating the area under the curve measured (possibly between predefined temperatures) by these sensors and dividing this area by the mass in mg of the sample, possibly using a correction factor.Alternatively, other methods of measuring the amount of HC can be used.

[0075] According to one embodiment of the invention, the temperature sequence under inert atmosphere according to the invention can be preceded by a temperature rise phase of the pyrolysis oven, which can be in the form of a thermal gradient, for example between 1 and 50°C / min, preferably between 20 and 25°C / min, or any other form of temperature rise curve of the pyrolysis oven. This preliminary heating phase of the pyrolysis furnace allows the furnace to reach the initial temperature of the inert atmosphere temperature sequence according to the invention. This preliminary phase can help initiate the thermal cracking of compounds whose cracking temperature is lower than the initial temperature of the inert atmosphere temperature sequence according to the invention.

[0076] According to one embodiment of the invention, the temperature sequence under an inert atmosphere according to the invention can be followed by a phase of lowering the temperature of the pyrolysis oven, which can be in the form of a thermal gradient, for example, between -1 and -50°C / min, preferably between -20 and -25°C / min, or any other form of temperature decrease curve for the pyrolysis oven. This final phase of lowering the temperature of the pyrolysis oven allows, if necessary, to complete the thermal cracking of the compounds associated with the final temperature of the temperature sequence under an inert atmosphere according to the invention.

[0077] According to the invention, at the end of this step, a curve is obtained representing the quantity of HC released over time during the pyrolysis phase, hereafter denoted C(t). It is quite obvious to a person skilled in the art to go from a curve representing the quantity of HC released over time to a curve representing the quantity of HC released as a function of temperature C(T), since the temperature sequence (evolution of the temperature as a function of time T(t)) is known.

[0078] 2) Determination of a first indicator representative of thermal stability organic carbon in the sample based on the amount of HC measured

[0079] During this step, the aim is to determine a first representative indicator of the thermal stability of the organic carbon present in the sample, from the quantity of HC measured continuously during step 1) described above.

[0080] More specifically, according to the invention, it is a matter of determining a representative indicator of the thermal stability of the organic carbon of the sample considered, hereafter denoted R, according to the following formula, described in Sebag et al., 2016; Sebag et al., 2022. This thermal descriptor R is derived from a calculation based on the integration of temperature threshold surfaces of the Rock-Eval pyrolysis thermogram (peak S2):

[0081] R = ((A3 +A4 + A5) / 100)(2)

[0082] where A3, A4, and A5 correspond to the carbon content released as HC during the heating sequence under an inert atmosphere in a temperature range of 400–460°C, 460–520°C, and 520–650°C, respectively. Surface A3 corresponds to a thermal class of resistant organic carbon. Surface A4 corresponds to a thermal class of more resistant organic carbon. Surface A5 corresponds to a thermal class of refractory organic carbon.

[0083] According to one embodiment of the invention, the A3, A4, and A5 contents can be determined according to the following formulas: 100841 A3=i^“C(T)dT 100851 A4 = 4f“®C(T)dT

[0086] A5=

[0087] It is quite clear that the R indicator corresponds to a representative indicator of the thermal stability of the organic carbon of the sample, taking into account both the organic carbon released by the organic matter of the sample to be analyzed and by the plastic particles of the sample to be analyzed.

[0088] 3) Determination of a second indicator representative of stability thermal organic carbon of the sample from the predetermined ISMO parameter

[0089] During this step, starting from the predetermined ISMO parameter, a second indicator representative of the thermal stability of the organic carbon in the sample to be analyzed is determined according to a formula of the type:

[0090] R0 = (ISMO - b)la (3)

[0091] Where a and b are predetermined coefficients.

[0092] Indeed, the document (Ducasse et al, 2023) shows that the ISMO parameter measured for a biomass sample is linearly related to the parameter representing the thermal stability of organic carbon in a given sample as described in steps 1) and 2). We subsequently refer to a linear correspondence law linking the ISMO parameter to the thermal stability indicator of organic carbon.

[0093] Furthermore, the measurement of the ISMO parameter is independent of the microplastic content in a biomass sample to be analyzed. Indeed, the biochemical fractionation method on which the determination of the ISMO parameter is based does not take into account compounds inherent to plastics, particularly when it comes to nonpolar plastic particles such as PE, PP, etc., which represent at least 60% of the plastics found in the environment and more than 80% in biomass. In fact, none of the terms SOL-CEL, LIC, and Ct3 can measure compounds that would be derived from polymers. Moreover, this conclusion has been confirmed by laboratory tests comparing reference biomass samples with and without plastic particles.

[0094] Thus, the second indicator representing the thermal stability of the organic carbon of the sample to be analyzed defined by equation (3) is representative of the thermal stability of the proportion of organic carbon not from microplastics of the sample to be analyzed.

[0095] In other words, the R0 indicator as determined above corresponds to an indicator of the thermal stability of the organic carbon of the sample from the organic matter of the sample, and not of the microplastics present in the sample.

[0096] According to a particular embodiment of the invention, the coefficients a and b of equation (3) above can be determined as follows: from a plurality of reference samples for which the ISMO parameter is predetermined, the reference samples corresponding to biomass or being derived from biomass and the reference samples not containing microplastics, the following steps can be carried out:

[0097] - for each of the samples in the plurality of reference samples, we apply step 1) in order to determine a quantity of hydrocarbon compounds released for each reference sample;

[0098] - for each of the samples in the plurality of reference samples, we apply step 2) in order to determine a thermal stability indicator for each reference sample;

[0099] - we determine the slope a and the y-intercept b of a law of linear correspondence linking the ISMO parameter to the thermal stability indicator of organic carbon by means of a linear regression method applied to the thermal stability indicators determined for each reference sample of the plurality of reference samples and to the predetermined ISMO parameters for each reference sample of the plurality of reference samples.

[0100] According to one embodiment of the invention, the coefficient a of equation (2) can be between 100 and 150, and is preferably 123, and / or the coefficient b of equation (2) can be between 10 and 50, and is preferably 22. The Applicant has in fact been able to establish, from a plurality of reference samples for which the value of the ISMO parameter is known and to which the particular embodiment described above has been applied, that the coefficients a and b of the correspondence law of equation (3) are included in the preferred values ​​above.

[0101] Thus, the value of the ISMO parameter being independent of the microplastic content contained in the sample, the second thermal stability indicator R0, determined from the ISMO and coefficients of a correspondence law determined on reference samples not including microplastics, is representative of the thermal stability indicator of the organic matter of the sample, without plastics.

[0102] 4) Determination of the quantity of microplastics in the sample

[0103] During this step, the quantity of QMP microplastics (for example, a content in mg per g of sample) present in the sample to be analyzed is determined according to a formula of the type:

[0104] QMP = [i / ^C(T)dT]*(RJ?0) [mgHC / g] (4)

[0105] Which can be written:

[0106] QMP=S2x (Rq-R)

[0107] where S2 corresponds to the area of ​​the portion of the curve C(T) weighted by the mass of the sample (expressed in mgHC / g of sample) between intermediate temperatures T1 and T2 of the temperature sequence according to the invention, T1 preferably being between 150°C and 300°C and most preferably being 200°C, and T2 preferably being between 600°C and 700°C and most preferably 650°C. Furthermore, m is the mass of said sample, C(T) the curve of the evolution of organic compounds released by the sample as a function of temperature during heating the sample. The term S2 corresponds to the measurement of the cumulative signal by the hydrocarbon compound detector (for example, in the form of a flame ionization detector (FID)) during pyrolysis, which is then converted into mg HC / g rock, taking into account the mass of sample used.

[0108] According to one embodiment of the invention, the amount of carbon in the microplastic sample can be determined by multiplying the quantity QMP by a stoichiometric coefficient of the form 100 / x, where x = % is the percentage of carbon (C) in the microplastic MP considered. By way of non-limiting examples, for PE, x can be 87 + / - 4%, and for PP, x can be 90 + / - 1%.

[0109] The difference between the first and second indicators corresponds to the portion of the first thermal stability indicator R due to microplastics, since the second indicator R0 does not take microplastics into account. Thus, equation (4) allows us to determine the quantity of microplastics present in the sample.

[0110] Furthermore, the invention relates to a system for quantifying the microplastic content in a biomass or biomass-derived sample for implementing the process according to any of the variants or combinations of variants described above, comprising a pyrolysis furnace in an inert atmosphere for carrying out said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for determining said first indicator R representing the thermal stability of the organic carbon present in the sample, said second indicator R0 representing the thermal stability of the organic carbon present in the sample, as well as the quantity of microplastics in said sample. In other words, the analytical means are suitable for implementing the steps of the process according to the invention, in particular steps 2 to 4.Analytical tools may include computer-based tools such as a computer, a processor, or a calculator. Examples

[0111] The characteristics and advantages of the process according to the invention will become clearer upon reading the application examples below.

[0112] The process according to the invention was applied to samples of three different types of urban biomass (Biodechets, Green Waste, Household Waste), collected in situ between 1998 and 2019 for each type of biomass: - PRO1, which corresponds to biomass of the green waste type..., - PRO2, which corresponds to biomass of the biowaste type..., - PR03, which corresponds to household waste-type biomass...,

[0113] Figure 2 shows, in solid lines, the linear correspondence law representing the evolution of the ISMO parameter as a function of the thermal stability indicator RO, defined by the highly preferential values ​​described above (i.e., with coefficients a equal to 123 and b equal to 22), and, in dashed lines, the lines obtained from the standard deviation of the coefficients a and b determined by linear regression as described above. Furthermore, Figure 2 shows: - in the form of squares, the values ​​of the first indicator R determined at the end of step 2) for the PRO1 samples, as a function of the predefined ISMO parameter values ​​for these samples; - in the form of triangles, the values ​​of the first indicator R determined at the end of step 2) for the PRO2 samples, according to the values ​​of the ISMO parameter predefined for these samples; - in the form of stars, the values ​​of the first indicator R determined at the end of step 2) for the PRO3 samples, according to the predefined ISMO parameter values ​​for these samples.

[0114] It can be observed in [Fig. 2] that the PRO3 type samples deviate significantly from the correspondence law described above, even taking into account the uncertainties in this correspondence law. The same is true for a PRO2 type sample. It can therefore be concluded that there is a high presence of microplastics in the PRO3 sample, regardless of the year considered, and the same is true for at least one PRO2 sample.

[0115] Fig. 3A (respectively Fig. 3B and Fig. 3C) presents in the form of a histogram the percentage of microplastics %MP contained in PRO1 type samples (respectively PRO2 and PRO3) for the years 1998, 2002, 2006, 2015 and 2019. We can observe on these histograms a very low presence of microplastics in PRO1 type samples (content less than 0.5%, or 5 kg of microplastics / T of dry PRO3 sample) while we can observe a higher presence of microplastics in PRO3 type samples (content of 4% in 2006 for example, or 40 kg of microplastics / T of dry PRO3 sample). For PRO2 type samples, the sample taken in 2019 shows the presence of microplastics (content of 2.5% or 25 kg of microplastics / T of dry PRO2 sample).

[0116] Thus, the present invention allows the quantification of microplastics present in a biomass sample (ISMO method and deconvolution) or in an amended surface formation (deconvolution) in a simple, rapid, and reliable manner, without destroying the organic matter. The method according to the invention is, in particular, simpler, faster, and therefore more economical than the methods according to the prior art. employing thermal spectroscopic analysis, this method does not require the destruction of organic matter to quantify plastic particles smaller than 250 µm. Indeed, the process according to the invention requires only a single heating sequence, in this case pyrolysis (saving the need for an oxidation furnace, CO and CO2 detectors, and energy for oxidation heating, with a duration of approximately 40 minutes instead of 1 hour 30 minutes according to the prior art). Furthermore, the process according to the invention allows for more reliable characterization of microplastics than the prior art. This is because the invention focuses on integration between temperature thresholds rather than peak deconvolution.Furthermore, the invention makes it possible to carry out rapid screening on very small quantities (a few mg of biomass) of a large number of biomass samples with a quantity of MP (in kg of microplastics / T of dry sample) which is not at all implemented today in agricultural or energy sectors.

Claims

1. Demands A method for quantifying the microplastic content in a sample of biomass or derived from biomass, based on an organic matter stability index for said predefined sample, characterized in that it comprises at least the following steps: A) said sample is heated in an inert atmosphere according to a predefined temperature sequence of which an initial temperature (TO) is between 100 and 300 °C, and a final temperature (TF) is between 650 and 800 °C, said temperature sequence comprising at least a thermal gradient between 1°C / min and 50°C / min, and at least a quantity of hydrocarbon compounds released during said heating sequence in an inert atmosphere is continuously measured; B) A first indicator R, representative of the thermal stability of the organic carbon present in the sample, is determined from the quantity of hydrocarbon compounds measured continuously and according to a formula of the type: R = ((A3 + A4 + A5) / 100) Where A3, A4, and A5 correspond to an organic carbon content released in the form of hydrocarbon compounds during said heating sequence under an inert atmosphere in a temperature range of respectively between 400 and 460°C, between 460-520°C and between 520-650°C; C) A second indicator R0 is determined, representative of the thermal stability of the organic carbon present in the sample, according to a formula of the type: R0 = (ISMO - b) / a where ISMO is said organic matter stability index for said predefined sample, and a and b are predetermined coefficients; D) The quantity of microplastics QMP in the sample is determined according to a formula of the type: QMP f™C(T)dT T1 being preferably between 150°C and 300°C and most preferably 200°C, and T2 being preferably between 600°C and 700°C and most preferably 650°C, m the niasse of said sample, C(T) the curve of the evolution of organic compounds released by the sample as a function of temperature during heating of the sample.

2. A method according to claim 1, wherein the amount of carbon in the microplastic sample is determined by multiplying the amount QMP by a stoichiometric coefficient of the form 100 / x with x the percentage of carbon of the microplastic considered.

3. A method according to any one of the preceding claims, wherein said organic matter stability index is determined for said sample by means of a biochemical fractionation method, preferably according to AFNOR standard FD U44-162 (07 / 2016), and a method for measuring carbon mineralization at 3 days, preferably according to standard FD U44-163 (02 / 2018).

4. A method according to any one of the preceding claims, wherein said organic matter stability index is determined for said sample by means of the following formula: ISMO = 445 + 0.5*SOL- 0.2*CEL+ 0.7*LIC - 2.3*Ct3, with SOL the soluble fraction of said sample, CEL a cellulose equivalent of said sample, LIC a lignin and cutin equivalent of said sample and Ct3 the content of mineralized exogenous organic carbon after three days of controlled incubation.

5. A method according to any one of the preceding claims, wherein said temperature sequence under inert atmosphere comprises a first isothermal plateau at the initial temperature (T0), followed by a predetermined thermal gradient so as to raise the temperature of the sample up to the final temperature (TF).

6. Method according to claim 5, wherein said temperature sequence may include a second isothermal plateau at the final temperature (TF).

7. A method according to any one of the preceding claims, wherein said temperature sequence comprises at least one isothermal plateau at an intermediate temperature between said initial temperature (T0) and the final temperature (TF).

8. A method according to any one of the preceding claims, wherein the contents A3, A4 and A5 are determined according to the following formulas: A3 = i^°C(T)dT A4 = i©;(T)dT A5= àf™0C(T)dT With m the mass of said sample, C(T) a curve of the evolution of hydrocarbon released by the sample as a function of temperature during heating of the sample.

9. A method according to any one of the preceding claims, wherein the coefficients a and b are predetermined from a plurality of reference samples, for which said organic matter stability index for said sample is predetermined.

10. A method according to any one of the preceding claims, wherein the coefficient a is between 100 and 150, and preferably 123, and the coefficient b is between 10 and 50 and preferably 22.

11. System for quantifying the microplastic content in a sample of biomass or derived from biomass for the implementation of the process according to any one of the preceding claims, comprising an inert atmosphere pyrolysis furnace for carrying out said temperature sequence, means for measuring hydrocarbon compounds at the outlet of said pyrolysis furnace, and analytical means for determining said first indicator R representative of the thermal stability of the organic carbon present in the sample, said second indicator R0 representative of the thermal stability of the organic carbon present in the sample, and the quantity of microplastics in said sample.

Images