Use of a hyperaccumulator plant to supplement biomass with trace elements in an anaerobic digester

Abstract

Process for producing biogas from biomass comprising feeding an anaerobic digester with biomass, and with at least one hyperaccumulator plant.

Description

Description Title of the invention: Use of a hyperaccumulator plant to supplement biomass with trace elements in a digester anaerobic

[0001] — The present invention relates to the use of a hyperaccumulator plant for biogas production.

[0002] = Biogas is the gas produced during the degradation of organic matter in The absence of oxygen (anaerobic fermentation), also called methanation. It can This could be a case of natural degradation — as seen in marshes or landfills household waste — but biogas production can also result from metha- waste disposal in a dedicated reactor, under controlled conditions, called a methanizer or digester, then in a post-digester, similar to the digester and allowing the methanation reaction to be pushed further.

[0003] — Biomass shall be defined as any grouping of organic matter that can be transforming into energy through this methanization process, e.g., sewage sludge wastewater treatment, manure / slurry, agricultural residues, energy crops, food waste comments…In Europe, agricultural residues and energy crops (dedicated or inter- medians) represent a large share of the biomass processed, particularly in Germany and Austria, then France. In Germany, 15% of agricultural digesters are operated in mono-digestion, that is, with 100% cultures. The majority of di- farmers mix the crops with manure / slurry (co-digestion).

[0004] The digester, that is to say the reactor dedicated to the methanization of biomass, is a closed tank, heated or not (operation at a fixed temperature, between the temperature ambient and 55°C) and whose biomass content is stirred, continuously or Sequential. The conditions in the digester are anaerobic and the biogas generated is is found in the digester headspace (gaseous space), where it is drawn off. The post- digesters are similar to digesters.

[0005] — By virtue of its main constituents — methane and carbon dioxide — biogas is a powerful greenhouse gas; it also constitutes, at the same time, a source of energy a valuable renewable resource in a context of dwindling fossil fuel reserves.

[0006] Biogas consists mainly of methane (CH4) and carbon dioxide (CO2) in varying proportions depending on the method of production and the substrate but may also contain, in smaller proportions, water, nitrogen, and hydrogen sulfide (H2S), oxygen, and other organic compounds, to the trace state, including H2S, between 10 and 50,000 ppmv.

[0007] — Depending on the organic matter degraded and the techniques used, the proportions components differ, but on average biogas contains, on a dry gas basis, 30 to 75% methane, 15 to 60% CO2, 0 to 15% nitrogen, 0 to 5% oxygen and trace compounds. Biogas is utilized in various ways. After light treatment, it can be used near the production site to provide heat, electricity, or a mixture of both (cogeneration). Or, after more extensive treatment, it can be purified into biomethane, which is used as a replacement for fossil natural gas, e.g., for clean transportation. In mono-digestion, or sometimes co-digestion, trace element deficiencies can occur in the digester. Trace elements are present in low concentrations and are necessary for the growth and function of anaerobic digestion bacteria. Depending on the substrate added, some trace elements may be found in insufficient concentrations. This disrupts the anaerobic digestion process, thus limiting biomethane production (Table 1). For example, nickel (Ni) deficiencies are common when using energy crops. [Table 1] Ni Co Mo Fe Mn Cu |Se w Zn |Recommendation |4-30 [04-10 pe 10-80 |0.05- [0.1-3 |30-400 6 |ooo |so0 4 o |Corn silage [2.67 0.008 [Lo9 [872 [204 [467 |202 |ND [No |Corn silage [2.67 [0.008 Lo9 [87.2 [204 |4.67 |202 |ND |Not analyzed | Cattle manure | |76 |188 [279 |1072 [337 |63.2 [0.631 [0.401 |319 Recommendation of trace element levels (mg / kg DT) and comparison to their levels in agricultural substrates. ND: not detected Trace element solutions are available on the market (OMEX, Aquafix, Schmack Biogas, etc.) to supplement the digester and improve its performance. Existing commercial trace element solutions have certain drawbacks: Cost of the solutions, even if it remains relatively low compared to the cost of biomass or gas production and purification processes, No intrinsic methanogenic potential, which would provide an additional advantage. complementary to the improvement of bacterial performance, A mix of solutions, generally ready-made, which do not necessarily target the specific deficiencies of the digester, A "chemical" image of added substances, not in line with the The environmentally friendly and natural approach of methanization. From this point, a problem that arises is to provide an improved trace element supplement in the digester. One solution of the present invention is a process for producing biogas from biomass comprising feeding an anaerobic digester with biomass, and with at least one hyperaccumulator plant. A "hyperaccumulator plant" is defined as a plant capable of storing contaminant concentrations in its tissues at least ten times higher than those found in other plants growing in the same soil. These contaminants are primarily stored in the easily harvestable aerial parts of hyperaccumulator plants. In this case, we will be focusing specifically on plants that hyperaccumulate heavy metals, particularly nickel and copper. In other words, the solution according to the invention makes it possible to add hyperaccumulative plants instead of and / or in addition to commercial solutions to stimulate anaerobic digestion. The addition of hyperaccumulator plants would allow digesters to be supplemented with certain substances, in a natural way, with an additional methanogenic potential provided in a targeted manner, depending on the plants selected. Depending on the case, the method according to the invention comprises one or more of the following characteristics: the hyperaccumulator plant is crushed before being introduced into the digester. biomass and the hyperaccumulator plant are introduced simultaneously in the digester. The biomass and the hyperaccumulator plant are ground together. the hyperaccumulator plant has a dry matter comprising at less nickel or copper per kilogram of dry matter. the hyperaccumulator plant is Alyssum Murale. the process includes a step of measuring the concentration CI in at least a trace element (O) in biomass; a comparison step of the concentration C1 with a setpoint value CO; and an introduction step of a plant that hyperaccumulates the trace element (O) in the digester when the concentration C1 is less than the setpoint value C0. the amount of hyperaccumulator plant introduced into the digester corresponds at each instant t of the process to a value in weight of the quantity of biomass introduced into the digester. The process includes, after feeding the digester with organic matter, the following: and in a hyperaccumulator plant, a step in the mixing of organic matter and the hyperaccumulator plant. The present invention also relates to a biogas production system comprising: A biomass production unit; An anaerobic digester; A means of introducing biomass into the digester; A means of introducing the hyperaccumulator plant into the digester; and A method of recovering a biogas stream at the outlet of the digester. Depending on the case, the installation according to the invention may include one or more of the following characteristics: The facility includes a hyperaccumulator plant production unit. The hyperaccumulator plant production unit includes a plot of land which the soil has a nickel content exceeding 50 mg / kg of dry matter and / or a copper content greater than 100 mg / kg of dry matter, the installation includes a means of recovering digestate from the outlet of the digester and a means of using the digestate as fertilizer in the unit of biomass production. The installation includes a means of measuring the concentration of Cl in the minus a trace element in biomass and a means of comparison of the Cl concentration with a CO setpoint value. Note that the means of The measure may include a means of taking a sample of the biomass and an on-site or off-site means of measuring Cl concentration in the minus one trace element in this sample. Finally, the present invention relates to the use of a hyperaccumulator plant to supplement biomass with trace elements in an anaerobic digester and stimulate anaerobic digestion. Indeed, the hyperaccumulator plant exhibits intrinsic methanogenic potential. The invention is a method for stimulating anaerobic digestion and increasing biomethane production, through the addition of hyperaccumulator plants, preferably crushed, in particular Alyssum Murale, which is rich in Ni, an element often deficient in the case of mono-digestion of agricultural materials such as corn. These hyperaccumulator plants allow for the natural supply of trace elements essential to the growth and functioning of digester bacteria. Furthermore, this method can be integrated into a broader environmental approach. Not only do hyperaccumulator plants enhance the performance of anaerobic digestion, but they also contribute to soil remediation. Projects are studying the extraction of metals from these plants (phytomining), but No commercial successes have yet been achieved in this area. Hyperaccumulators are therefore not yet valued as such. Several hundred hyperaccumulator plants exist. The prime example is Alyssum murale. This is a well-known hyperaccumulator, studied in the remediation of nickel-contaminated soils. Since nickel is frequently present in insufficient quantities in the biogas production of energy crops, this plant is potentially valuable for inclusion. Studies indicate that up to 15-30 mg Ni / kg dry matter can be accumulated, depending on the plant part. Other plants could also be involved, albeit to a lesser extent, such as L. perenne, which accumulates copper, up to 10 mg / kg. Grinding plants increases the availability of trace elements. Plants can therefore be incorporated whole, directly with biomass, with or without grinding.

Claims

Demands

1. Process for producing biogas from biomass comprising feeding an anaerobic digester with biomass, and with at less a hyperaccumulator plant.

2. A biogas production process according to claim 1, characterized in the hyperaccumulator plant is crushed before being introduced in the digester.

3. A biogas production process according to claim 1 or 2, characterized in that the biomass and the hyperaccumulator plant are introduced simultaneously into the digester.

4. A biogas production process according to any one of claims 1 to 3, characterized in that the biomass and the hyperaccumulator plant are crushed together.

5. A method for producing biogas according to any one of claims 1 to 4, characterized in that the hyperaccumulating plant exhibits a substance dry containing at least 10 mg of nickel or copper per ki- dry matter graph.

6. A biogas production process according to claim 5, characterized in The hyperaccumulator plant is Alyssum Murale.

7. A method for producing biogas according to any one of claims 1 to 6, characterized in that the process comprises: A step of measuring the concentration C1 in at least one trace element in biomass; A step of comparing the concentration C1 with a CO setpoint value; A step in introducing a hyperaceumulating plant of the trace element (O) in the digester when the concentration CI cst is less than the setpoint value CO.

8. A biogas production process according to any one of claims 1 to 6, characterized in that the quantity of hyperaccumulator plant introduced in the digester corresponds to each instant t of the process to a value between 5 and 15% by weight of the quantity of biomass introduced in the digester.

9. A method for producing biogas according to any one of claims 1 to 8, characterized in that it comprises, after feeding the digester into organic matter and in a hyperaccumulator plant a stage of Mixing of organic matter and the hyperaccumulator plant.

10. Biogas production facility comprising: A biomass production unit; An anaerobic digester; A means of introducing biomass into the digester; A means of introducing the hyperaccu- plant mulatrice in the digester; and A method of recovering a biogas stream at the outlet of the digester.

11. Biogas production installation according to claim 10, ca- characterized in that the installation includes a production unit of hyperaccumulator plant.

12. Biogas production installation according to claim 11, ca- characterized in that the hyperaccumulator plant production unit includes land whose soil has a high nickel content greater than 50 mg / kg of dry matter and / or a copper content exceeding greater than 100 mg / kg of dry matter.

13. Biogas production plant according to any one of claims 11 and 12, characterized in that it includes a means of recovering a digestate at the outlet of the digester and a means of using the digestate as fertilizer in the biomass production unit.

14. Installation according to any one of claims 10 to 13, characterized in that that it includes a means of measuring the concentration C1 in the minus a trace element in biomass and a means of comparison of the concentration C1 with a setpoint value CO.

15. Use of a hyperaccumulator plant to supplement the biomass in trace elements in an anaerobic digester and stimulate the anaerobic digestion.