Anaerobic digestion

Technology
Technology details
Name:	Anaerobic digestion
Category:	Conversion (Biochemical processes and technologies)
Feedstock:	Biowaste in general, Food waste, Garden and park waste (wood, leaves)
Product:	Biogas and digestate

Anaerobic digestion is a process through which micro-organisms break down organic matter, such as animal manure, wastewater biosolids, and food wastes, in the absence of oxygen. Anaerobic digestion intended for biogas production takes place in a sealed tank (called an anaerobic digester), which is designed and constructed in various shapes and sizes specific to the site and feedstock conditions. These sealed vessels contain complex microbial communities that break down the waste and produce biogas and digestate (i.e., the solid and liquid material end-products of the process). The biogas can be used as a source of energy. The remaining digestate can be used as a fertiliser, or it can be post-treated according to its intended use, e.g. by drying or composting to use it as a soil improvement agent.

Feedstock

Origin and composition

Multiple organic materials can be combined in one digester, a practice called co-digestion. Co-digested materials include, amongst others, manure, food waste, energy crops, crop residues, and fats, oils, and greases (FOG) from restaurant grease traps.

Pre-treatment

Biomass is first separated from impurities as stones and glass. An agitator provides a good mixing between different biomass types to avoid strong changes in composition. The feed is a stirrable mixture and the dry matter content may be a maximum of 15-20% of the slurry. Co-substrates are often reduced in size by shredding before they are fed in order to make the contact surface of the biomass as large as possible.

For residual flows from the food industry, crop residues and manure, thermal and chemical pre-treatments are mainly applied. The most important effects of thermal pre-treatment are: reducing particle size, increasing solubility and improve the biodegradability. Additional advantages of thermal pre-treatment are: (1) higher loading of the digester is possible, (2) lower viscosity of the treated material which results in lower energy input for mixing the digester, (3) improved dewaterability of digestate and (4) sanitised product.

The following pre-treatments may be considered :

• Membrane filtration
• Sieving
• Sizing (e.g. chipping, grinding)
• Thermal pre-treatment

Process and technologies

Process

There are three basic anaerobic digestion processes, namely psychrophilic, mesophilic, and thermophilic, which take place over different temperature ranges. Psychrophilic digestion is a low temperature (<20°C) process. Mesophilic digestion takes place between 20 and 45°C, which can take a month or two to complete, and thermophilic digestion between 45 and 65°C, which is faster, but its micro-organisms are more sensitive. The majority of the agricultural biogas plants are operated at mesophilic temperatures. Thermophilic temperatures are applied mainly in large-scale centralised biogas plants with co-digestion. The process of anaerobic digestion takes place through four successive stages: hydrolysis, fermentation, acetogenesis, and methanogenesis. In the hydrolysis step, the feedstock is broken down into soluble substrates (e.g., sugar and amino acids) by enzymes. Fermentation involves the conversion of sugar, amino acids, and fatty acids into ammonia, organic acids, hydrogen (H₂) and CO₂. In the acetogenesis step, volatile fatty acids are broken down into acetic acids, CO₂ and H₂. Finally, methanogenesis step converts acetate, formaldeyde, and H₂ to CH₄ and water.

Simplified scheme of pathways in anaerobic digestion (not own work)

Usually, the produced biogas must be dried and drained for condense water and biological or chemical cleaned for H₂S, NH₃ and trace elements. Further upgrading of the biogas to increase the CH₄ content could be realized by membrane separation of CO₂ and pressurising the biogas.

A main distinction between anaerobic digestion (AD) technologies for treatment of municipal and industrial biodegradable wastes is the operating process solids content. Wet AD systems operate at low total solids (<10–20% TS) and dry systems have high operating solids (20–>40% TS).

Product

Anaerobic digestion produces two valuable outputs, namely biogas and digestate. Biogas is composed of methane (CH₄), which is the primary component of natural gas, at a relatively high percentage (50 to 75%), carbon dioxide (CO₂), hydrogen sulfide (H₂S), water vapor, and trace amounts of other gases. The energy in biogas can be used like natural gas to provide heat, generate electricity, and power cooling systems. Biogas can also be purified by removing the inert or low-value constituents (CO₂, water, H₂S, etc.) to generate renewable natural gas (RNG). This can be sold and injected into the natural gas distribution system, compressed and used as vehicle fuel, or processed further to generate alternative transportation fuel or other advanced biochemicals and bioproducts.

The digestate can be used in many beneficial applications provided that is is appropriately treated post processing. This could be in form of animal bedding, nutreint-rich fertilizer, organic-rich compost, or as soil amendment.

Post-treatment

The remaining digestate can be post-treated according to its intended use, e.g. by drying or composting to use it as a soil improvement agent.

Technology providers

Technology comparison

Company name	Country	Technology subcategory	Technology name	TRL	Capacity [kg/h]	Processable mass [kg]	Temperature [°C]	Feedstock: Food waste	Feedstock: Garden & park waste	Product: biogas	Product: Renewable natrual gas (RNG)
Biogas Plus	The Netherlands	-	Compact Plus	9	-	-	-			●
Biorenewables Development Centre	United Kingdom	-	Anaerobic digestion	4	-	-	-	●	●
BioRenGaz	France	-	Bioreactor	7	-	-	-
Dranco	Belgium		DRANCO Dry anaerobic digestion	-	5000	-	-	●
Planet Biogas	Germany	-	PlanET	9	-	-	-	●	●	●

Biogas Plus

Anaerobic digestion provider

General information
Company:	Biogas Plus
Country:	The Netherlands
Contact:
Webpage:	https://www.biogasplus.nl
Technology and process details
Technology name:	Compact Plus	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	9	Capacity:	18.000 tons (input), 320.000 Nm3 green gas/year (output). kg·h-1
Atmosphere:		Catalyst:
Pressure:	bar	Reactor:	Complete mix digester
		Other:
Feedstock and product details
Feedstock:	Animal Manure	Product:	Green gas

Biogas Plus is a turnkey supplier of biogas installations. This biogas installation produces biogas through the fermentation of organic (residual) flows, such as manure, unpacked food, sewage treatment sludge or other products. The biogas is then upgraded to renewable gas (green gas / biomethane / RNG) or to green electricity and heat. Biogas Plus offers a variety of installation sizes able to meet the needs of a mid-size farm up to large-scale units (between 50.000 and 300.000 tons of input per year).

Biorenewables Development Centre

Anaerobic digestion provider

General information
Company:	Biorenewables Development Centre
Country:	UK
Contact:	Deborah Rathbone
Webpage:	https://www.biorenewables.org/
Technology and process details
Technology name:	anaerobic digestion	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	4	Capacity:	kg·h-1
Atmosphere:		Catalyst:
Pressure:	bar	Reactor:	up to 30L
		Other:
Feedstock and product details
Feedstock:	food waste, agricultural wastes, industrial wastes	Product:

The Biorenewables Development Centre )BDC) has anaerobic digestion (AD) facilities that enables new/potential users of AD to characterise their feedstock to establish its suitability for production of high biomethane yields, and also help existing users of AD systems to test modifications or additions to their system. Our facilities comprise;

• Custom built low (3-5%) and high (~25%) solids contents systems: 30 L reaction volume; pH- and temperature-controlled stirred digester units with integral dewatering system to facilitate the continuous addition of high volumes of dilute feedstocks.
• 24 unit biomethane potential analysis (BMP) system
• Hach Lange BOD Trak II for biochemical oxygen demand (BOD) analysis
• Hach Lange DR3900 spectrophotometer with HT200 high temperature / high speed digestion unit for measurement of chemical oxygen demand (COD), organic acids, nitrogen, chloride etc
• A range of Hewlett Packard and SRI gas chromatography systems (TCD, FPD, FID and Methanizer detection systems) to measure gas composition
• Thermolyne muffle furnace
• Kern moisture balance
• Hach Lange TOC5 shaker
• Hach Lange Titralab AT1000 titration system
• Portable pH, DO and conductivity systems
• Robot Coupe Blixer 10 VV for sample homogenisation
• Gas detection / oxygen depletion detection system

BioRenGaz

Anaerobic digestion provider

General information
Company:	BioRenGaz
Country:	France
Contact:	contact@biorengaz.com
Webpage:	https://www.biorengaz.com/
Technology and process details
Technology name:	Bioreactor	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	7	Capacity:	kg·h-1
Atmosphere:		Catalyst:
Pressure:	bar	Reactor:
		Other:
Feedstock and product details
Feedstock:		Product:

BioRenGaz has developed a new patented anaerobic digestion technology that is 4 times more efficient and much more compact than conventional biogas plants thanks to vertical silo design. The anaerobic filter uses a recycled and 100% renewable packing material to replace costly and polluting plastic packing. This medium provides an ecological habitat for the bacteria and enhances their performance. The solution is adapted for the treatment of liquid effluents and the great advantage, unlike other technologies, is that it can also valorize pulpy effluents like biowaste pulp. The bioreactors have lower operational costs and increased energy production by keeping the micro-organisms on the packing material, which allows producing 10% more biogas. The system is modular, so bioreactors can be built from a small scale and easily be expanded as needed. The Solution aims for the optimization of the economic and environmental model of energy and agronomic recovery of biowaste.

Dranco

Anaerobic digestion provider

General information
Company:	DRANCO nv
Country:	Belgium
Contact:	Bruno Mattheeuws (bm@dranco.be)
Webpage:	https://www.dranco.be
Technology and process details
Technology name:	DRANCO Dry anaerobic digestion	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	Successful Deployment	Capacity:	>5000 kg·h-1
Atmosphere:		Catalyst:
Pressure:	bar	Reactor:	2500-5000m³
		Other:
Feedstock and product details
Feedstock:	biowaste, SSO, MSW, residual waste, ...	Product:	Digestate and/or high quality compost + biogas

DRANCO nv has developed innovative and patented designs for biogas plants, with a pretreatment, digester concept and post-treatment adapted to each type of feedstock.  Find out about our 30+ years of experience and our 35 references!

PlanET Biogas Group GmbH

Anaerobic digestion provider

General information
Company:	PlanET Biogas Group GmbH
Country:	Germany
Contact:
Webpage:	https://www.planet-biogas.com
Technology and process details
Technology name:	PlanET	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	9	Capacity:	kg·h-1
Atmosphere:		Catalyst:
Pressure:	bar	Reactor:	Complete mix digester (modular)
		Other:
Feedstock and product details
Feedstock:	Animal manure, biogenic waste materials	Product:	Green gas, heat & electricity

PlanET anaerobic digestion (AD) plants can convert almost all biogenic waste materials into energy, such as slaughterhouse waste, fish processing residuals, animal carcasses, expired food or off-specification batches used in food production as well as agricultural residues, fats and oils. PlanET Biogas’ portfolio covers the whole range of biogas technology and utilization: feeding technology, safety technology, energy concepts, hygienisation, and gas upgrading. PlanET Biogas offers its technology turn-key and provides all after-sale services including biological assistance as well as service and maintenance for all technical equipment. PlanET Biogas has completed 600 AD plants worldwide, from 40 kW liquid manure systems to 3 MW waste to energy plants.

Open access pilot and demo facility providers

Here we make the link to the Europe-wide network & database of open access multipurpose pilot and demo infrastructures for the European bio-economy.

If you are looking for shared facilities that exist for the technology of anaerobic digestion, here is the link to the selection from the Pilots4U database : Pilots4U Database

Patents

Currently no patents have been identified.