Inputs (or deposits) of methanization

Technical articles

Agricultural_methanization Methanization Digestate Methanization_recipe Methanization_inputs Methanization_sources

Inputs or sources are the organic materials used by methanization to produce biogas. They are characterized by their methanogenic power (or potential) (BMP), that is to say by the amount of methane they produce during their degradation in the methanization process (anaerobic condition).

Different inputs

The decree of November 23, 2011 (modified by the decree of June 24, 2014) defines the nature of inputs in biomethane production:

• Agricultural waste (manure, slurry, crop residues…)
• Agri-food industry waste (fruits, vegetables, slaughterhouse waste…)
• Urban waste (biowaste from: household, catering or large/medium retail)
• Industrial waste (industrial process wash water, industrial sludge)

File:Methanogenic potential of different substrates.jpg

File:Electric power generated by different substrates.jpg

Electric power generated by different substrates

Agricultural waste

Methanogenic potential

• Waste from livestock

Category	Methanogenic potential
Calf slurry	463 m3 CH4/t of organic matter (OM)
Cattle slurry, cow, heifer	274 m3 CH4/t OM
Manure, slurry cattle	260 m3 CH4/t OM
Goat manure	281 m3 CH4/t OM
Rabbit manure/slurry	250 m3 CH4/t OM
Horse manure	323 m3 CH4/t OM
Sheep manure	249 m3 CH4/t OM
Pig manure	253 m3 CH4/t OM
Poultry manure/droppings	289 m3 CH4/t OM

• Waste from Category:Crops

Category	Methanogenic potential
Jerusalem artichoke, silphium (whole plant/ensilage)	284 m3 CH4/t OM
Beets (silage, sugar beet (whole or not))	371 m3 CH4/t OM
Cereals (whole plant/ensilage)	283 m3 CH4/t OM
Forage (whole plant/ensilage)	276 m3 CH4/t OM
Oilseed protein crops (whole plant/ensilage)	332 m3 CH4/t OM
Temporary grassland (silage or not)	275 m3 CH4/t OM
Straw	247 m3 CH4/t OM
Fresh algae	321 m3 CH4/t OM
Non-fresh algae	133 m3 CH4/t OM

Food industry waste

Methanogenic potential

Category	Methanogenic potential
Fats	629 m3 CH4/t OM
Wine lees	326 m3 CH4/t OM
Hop marc	525 m3 CH4/t OM
Fruit marc	344 m3 CH4/t OM
Bakery	421 m3 CH4/t OM
Confectionery	441 m3 CH4/t OM
Starch factory/ potato processing	381 m3 CH4/t OM
Fruit and vegetable processing/canning	347 m3 CH4/t OM
Fats from margarine production, edible oils	703 m3 CH4/t OM
Oilcakes/brans	375 m3 CH4/t OM
Lactose/whey/skimmed milk	399 m3 CH4/t OM
Cream/cheese/whole milk/whey	466 m3 CH4/t OM
Seafood products	250 m3 CH4/t OM
Starch factory	391 m3 CH4/t OM
Sludges	499 m3 CH4/t OM

Urban waste

Methanogenic potential

Category	Methanogenic potential
Catering waste	498 m3 CH4/t OM
Large and medium retail	409 m3 CH4/t OM
Unpacking soup	487 m3 CH4/t OM
Grass clippings	80 m3 CH4/t OM
Fats from WWTP, flotation and sewage treatment plants	733 m3 CH4/t OM
Green waste juice	401 m3 CH4/t OM

On January 1, 2024, the law imposed source sorting of biowaste and their valorization, notably by composting or methanization. This source represents an important resource (5 to 9 TWh/year according to ADEME) that could be valorized in partnership with local authorities.

The use of biowaste in methanization may require an additional unpacking step (in case of packaging) carried out at the methanization site or in a central unpacking unit that groups waste for several methanizers (it must then be located near the biowaste production and methanization site).

To have a balanced digestate, it is recommended to incorporate biowaste as a complement to agricultural waste, indeed, the composition of a digestate from degradation of biowaste alone:

• is poor in organic matter
• has a low C/N ratio
• is rich in N, P, K

File:Digestate composition from biowaste.jpg

Digestate composition from biowaste

Industrial waste

Methanogenic potential

Crude glycerin, for example, has a methanogenic potential of 734 m³ CH₄/t OM

Storage of inputs

Inputs must be stored in a way that prevents any risk of contamination, however the precise rules on storage conditions depend on the sanitary regulations of each department, the storage location (on the farm, at the methanization unit) as well as the ICPE regulation (Classified Installation for Environmental Protection) to which the methanization unit is subject.

There are general recommendations typical for each input, presented below.

For manure

• Reduce all contact with air to avoid accelerating the degradation of dry and fresh matter.
• Store manure under shelter in a confined mode to avoid dry matter losses due to rainwater in particular.
• Limit storage duration.
• According to laboratory tests (DEEP INSA Lyon), adding straw to obtain a dry matter content of 20-25% reduces microbial activity and thus biodegradation of the matter in confined storage.
• Co-storing cattle manure with a product rich in fermentable organic matter would allow ensiling conditions to establish (DEEP INSA Lyon).

⚠️It is mandatory to recover the leachate from manure and store it in sealed constructions (according to departmental sanitary regulations).

For plants

If plants are composed of less than 40% dry matter, it is recommended to preserve them by ensiling to avoid loss of organic matter and thus methanogenic potential.

If plants have between 40% and 80-85% dry matter, they must not be stored for long periods because there is a risk of heating and self-combustion.

If plants have more than 80-85% dry matter, they must be stored under shelter to limit losses of methanogenic potential and not be moistened.

For slurry

• Slurry should be, if possible, treated in just-in-time flow (or by limiting storage duration to 1 or 2 weeks maximum) because 90% of its methane potential is lost during the first 30 days of storage.
• Cover the storage pit to:
  • reduce odors and nitrogen losses by volatilization
  • avoid dilution of slurry causing additional volumes to store, treat and spread at output
• Tanks or pits must be emptied and cleaned between each use to eliminate suspended matter, which supports bacterial development causing methane potential losses.
• A mixing system allows homogenizing the matter before pumping it to the methanizer. However, this must be minimal to avoid promoting emissions of volatile compounds.

Regulation of animal by-products (ABP)

Methanization units using animal by-product sources are classified into different categories according to the type of source used and are regulated:

• at European level by Regulations No. 1069/2009 (EC) and No. 142/2011 (EU)
• at national level by decrees of 12/08/2011 and 04/09/2018

Obtaining sanitary approval

They must obtain a sanitary approval. For this, the person in charge of the methanization unit must:

• submit to the DD(CS)PP (Departmental Directorate of Social Cohesion and Population Protection) the sanitary approval file (presentation of the establishment and staff, description of the facilities and product manufacturing, and a sanitary control plan based on an HACCP method) as well as Annex I (cerfa) of the ministerial decree of 12/08/2001
• Request a derogation for hygienization if needed (see the paragraph “Possible derogations”)

After study of the file, a provisional approval (valid about 6 months) will be issued. Then, health authorities must visit the site and analyze the digestate to issue a final approval. After that, control visits will be conducted from time to time by competent authorities.

Classification of methanization units

Category 1 (C1) (closed list)	Category 2 (C2) (open list)	Category 3 (C3) (closed list)
Sick or suspected animals Animals used in experiments Rendering screening ABP containing prohibited substances (chloramphenicol…) or environmentally hazardous substances (PCB) Catering waste from international transport	Slurry, manure, droppings, dung… Stercoral matter Chicks dead in the egg and embryos Altered or exceeding threshold C3 ABP Raw milk from sick animals (tuberculosis…) Foodstuffs withdrawn/recalled for foreign body presence, health risk (salmonella, ETO,...)	Parts of healthy animals fit for slaughter or subparts from healthy animals By-products from the agri-food industry (AFI) or food production Former foodstuffs not altered and without risk Blood, placenta, raw milk, hatchery by-products, egg, feathers… from living non-sick animals Catering waste (CW) Former petfood and animal feed (livestock)

The ABP producer must provide a Commercial Accompanying Document (CAD) to the methanization unit manager and specify the ABP category generated.

Category 1 ABP

These ABPs are the most dangerous, they are prohibited in methanization and must be disposed of by incineration or landfill (after sterilization under pressure).

Category 2 ABP

These ABPs can be methanized after sterilization, meaning they must be reduced to particles with size less than 50 mm then heated to 133°C for 20 min under a pressure of 3 bars. After this step, hygienization is not mandatory (see paragraph “Category 3 ABP”).

Category 3 ABP

These ABPs can be methanized after undergoing a hygienization/pasteurization step, meaning they must be reduced to particles of size less than 12 mm, then heated above 70°C for at least 1 hour without interruption. The installation must be equipped with a continuous temperature monitoring system.

Possible derogations

The decree of 04/09/2018 specifies possible derogations to sterilization and hygienization:

• if C2/C3 materials and glycerin derived from melted fats (C1) are treated, it is possible to derogate sterilization/hygienization provided that the digestate produced is destroyed by incineration/co-incineration or transformed into compost (the transformed digestate is usable only in France).

• In the image below, some C2 materials (including slurry and manure) can derogate sterilization and some C3 materials can avoid hygienization, however they must be used alone or mixed with other sterilized/hygienized C2/C3 materials.

The digestate from this type of methanization undergoes no special treatment but can only be used in France.

File:Derogation manure slurry.jpg

Derogation for hygienization of manure and slurry

The technical institute specified in 2020 that no derogation can be granted for methanization units where:

• the annual tonnage of livestock effluents exceeds 30,000t
• livestock effluents come from more than about ten farms (the notion of ten, imprecise, depends on the interpretation of the person inspecting the derogation request)

Methanization recipe

Balancing the ration

Inputs are chosen according to several criteria:

• methanization processes
• local sources
• their methanogenic power
• digestion speed
• viscosity of the mixture (preferably not too viscous to avoid equipment failure)
• trace element contributions (they support the health of the bacteria in the digester)
• desired digestate composition
• …

It is possible to mix or not the types of inputs. When combined, it is more difficult to predict the impact of the mixture on digester operation or production optimization, however, co-digestion (mixing inputs of different nature) is advantageous because it allows:

• adjusting dry matter content (dilution of dry substrates by more liquid substrates)
• managing supply shortage risks
• complementarity and/or lifting deficiencies
• optimizing economic profitability of methanization units

To determine the most relevant recipe, laboratory analyses are necessary.

File:Typical ration of French units.jpg

Typical ration of French methanization units

Pre-treatment of inputs

Pre-treatments make the matter more easily degradable, generally applied to ligno-cellulosic biomass (rich in straw) to break the bonds between lignin and the matter easily degradable by digester microorganisms.

Mechanical pre-treatment

Mechanical pre-treatments include grinding, extrusion, crushing, defibrating and shredding.

This upstream step of the digester allows:

• increasing surface/volume ratio, so microorganisms have more access to matter and can degrade it more easily
• facilitating solubilization of organic compounds and thus reducing clogging problems
• increasing methanogenic potential and bioconversion kinetics of organic compounds into methane.
• shortening floating layers in liquid-phase processes
• minimizing sedimentation of dense particles in liquid phase as well

The disadvantages of this process are:

• the cost of equipment
• energy consumption

CH₄+ Project

Companies Agriopale and Methaplanet have filed a patent and are testing a machine capable of transforming inputs very rich in straw, such as horse manure, into pellets. According to their analyses, this pre-treatment would allow methane production levels exceeding 350 Nm³ CH₄/ton of manure.

Cavitation

Cavitation is a type of mechanical pre-treatment, it causes shocks that destroy the lignin structure, making matter more accessible to bacteria and thus increasing methanogenic potential. This process is generated by the rotation of a propeller, indeed, this movement creates a depression allowing the formation of an air bubble.

Thermal pre-treatment

Thermal pre-treatments are mainly implemented to hygienize the matter.

Chemical pre-treatment

Chemical pre-treatments consist of adding a chemical agent to the biomass before incorporation into the digester.

This process occurs:

• in the presence of acid by combining high dose/low temperature or diluted dose/high temperature. Use of these products requires corrosion-resistant reactors because the pH of the mixture entering the digester is between 1 and 4.
• at ambient temperature when the chemical agent is a base (the most effective bases are: calcium oxide or calcium hydroxide)
• by adding ozone (ozonation)
• by adding lime to inputs with high dry matter content (increasing methanogenic potential by 15%)

The main disadvantages of this step are:

• the price (chemical agents and equipment)
• possible formation of methanization inhibitory by-products
• environmental and health risks generated

Biological pre-treatment

Their principle is based on the use of microorganisms such as bacteria, filamentous fungi, but also on the use of enzymes (effective but expensive). They are presented as an alternative to other pre-treatment operations because they are non-energy intensive and do not require the use of reagents.

There are two types:

• a pre-aeration technique in aerobic conditions allowing the development of enzymes specific to lignin decomposition
• ensiling which stops biological activity through fermentation and pH drop

Comparative table of different pre-treatment types

	Typical ligno-cellulosic substrates/manures
	Advantages	Disadvantages
Mechanical pre-treatments	Practical installation at large scale No generation of inhibitory products Particle size reduction Improved fluidity in the digester	Energy consumption
Thermal pre-treatment	Hygienization	Risk of inhibitory compound production Energy consumption
Chemical pre-treatment	Significant improvement of biodegradability Moderate energy consumption	Formation of chemical compounds Cost
Biological pre-treatment	Moderate energy consumption	Specific implementation conditions Cost

Assistance provided by simulators

There are various tools that help optimize the methanization recipe.

Tool offered by GRDF

Depending on the methanization recipe, the simulator provides an order of magnitude for:

• the gas production of the methanization unit (in Nm³/h and kWh/year) as well as the relevance or not of considering an injection project according to the quantity of green gas produced
• the financial and agronomic potential of the methanization unit (annual turnover, quantity of digestate produced each year, biomethane purchase price, quantity of biogenic CO₂ produced)
• the equivalent in mineral nitrogen supplied by the digestate
• the environmental and local impact of the digester (number of households heated, number of tractors running on BioGNV, and number of jobs created)

Ferti-Dig (digestate class sheets)

This document written by RMT Bouclage in 2025 analyzes the predominant type of input in the methanization recipe and the consequences on various aspects of the digestate:

• its physico-chemical composition
• its capacity to maintain soil carbon stocks
• its nitrogen fertilizing value
• as well as spreading recommendations

ConceptDig

This tool designed by INRAE in 2021 provides indications on certain parameters of the digestate:

• the amendment potential
• the fertilizing potential
• the quantity of certain elements present in the digestate (organic matter, dry matter, C/N ratio, ammoniacal nitrogen…)

Conclusion

Methanization is part of a local waste recovery circuit, indeed, the inputs mainly come from nearby stocks and allow the production of a digestate usable on agricultural lands located around the digesters.

Source

• ADEME. 2020. Good practices for material storage before methanization. [13/11/2025]. https://www.bioenergie-promotion.fr/wp-content/uploads/2020/03/guide-methodologique-stockage-avant-methanisation-2020.pdf
• Aras Ahmadi, Marco Avila-Lopez. 2022. Guide for optimal energy practice of farm methanization for biogas production. [13/11/2025]. https://projet-methanisation.grdf.fr/cms-assets/2023/05/Guide-pour-une-pratique-energetique-optimale-de-la-methanisation-a-la-ferme_compressed-2.pdf
• ATEE. 30/09/2021. Material recycling and energy recovery of biowaste: issues and solutions provided by methanization. [13/11/2025]. https://atee.fr/system/files/2021-10/13_JJ_CTBM%20BIODECHETS%2030%20SEPTEMBRE%202021.pdf
• S. Berger, H. Carrere, I. Desneulin, F. Monlau, C. Peyrelasse. 2022. Storage and pretreatment of inputs before feeding methanization digesters, state of knowledge and recommendations. [13/11/2025]. https://solagro.org/images/imagesCK/files/publications/2023/2022_Rapport_Record.pdf
• Helen Laura Coarita Fernandez. 2021. Pretreatment of agricultural waste for optimizing its recovery by methanization. [13/11/2025]. https://theses.hal.science/tel-03411620v1/file/these.pdf
• GRDF. Inputs and organic waste for methanization. [13/11/2025]. https://projet-methanisation.grdf.fr/la-methanisation/la-methanisation-quest-ce-que-cest/les-intrants
• INRAE. 02/02/2022. Methanization: increasing biogas production by lime pretreatment. [13/11/2025]. https://www.inrae.fr/actualites/methanisation-augmenter-production-biogaz-pretraitement-chaux