Anaerobic Digestion Feedstock

The anaerobic digestion feedstock, and its reliable supply, is everything to an Anaerobic Digestion Process. The biggest successes come from close attention to the volume, nature, composition and variability in composition, of the available feedstock, or range of feedstocks to be accepted. These must be planned for from the outset when designing an AD Plant.

Feedstock and Anaerobic Digestion Processes

This is where the crop fed biofuel AD plant designer starts with a huge advantage on the rest of the AD developers. There will be seasonal variations from the available crops of course, unless year-round storage can be provided for total feedstock inputs, which may be feasible for silage feedstock use, for example.

Sewage sludge AD and agricultural waste fed AD processes are possibly the next in security of feedstock provision. Where anaerobic digestion plants are built to process industrial wastes these are also reasonably secure in the knowledge of the characteristics of their feedstock materials.

Image: Feedstock Conveyor at the Greenfinch Plant, Ludlow, UK

However, things can get really difficult for AD Plants being built to process primarily food waste from householders within the council collection service. When these plants are built it is at present an act of faith to know to what extend the public will segregate their wastes to send them to the AD Plant. The householders may decide to include these materials in the “black bag” mixed waste stream. Alternatively, the householders may even send these materials for composting, in the green/garden waste recycling bin.

[box type=”note”]Results differ widely for each feedstock. This table is a guide to typical values only. Analyse your own feed stock. Do not rely on the values in this table.[/box]

Furthermore, how does the designer predict what proportion of high calorific value/high methane generating food waste will arrive within the material collected for Anaerobic Digestion? In time maybe it will be possible to predict but this is a doubtful art at present.

If the AD designer gets it wrong the result will be that methane production rates may be at a lower or higher rate than predicted.  If the volume sent to the AD plant is low can negatively affect economic viability.

The solution for AD Plants which do not have the ability to directly control their own incoming feedstock quality, is to diversify. Operators should diversify, if possible to a variety of feedstocks available in season.

Feedstock choice is also then likely to vary over time, with the operator choosing to accept different feedstocks at economic prices. Prices will vary as market forces act on their market.

Potential Feed Anaerobic Digestion Plant Feed Materials

At Anaerobic-Digestion.com we are often asked whether a particular organic waste is suitable feedstock for AD treatment. So, we thought that we would devote a web page to providing a list of some of those we perceive to be the most common. Add a comment with your additions, if you have more to add, and this list will grow.

Another question posed is what is the biogas yield which can be expected from agricultural wastes, and this is answered in the table above.

Anaerobic Digestion Feedstock List

• Dairy Farm and piggery etc waste slurries
• Dairy Product and other Food Processing wastes
• Household Food Waste with or without Green Waste
• Brewing Industry effluents and wastes
• Supermarket Waste*
• Municipal Solid Waste from Kerbside collections of Green Waste
• Municipal Solid Waste from Kerbside collections of Green Waste and Kitchen Waste*
• Catering Industry Wastes*
• Organic Market Wastes*
• Sewage Treatment Works sludges
• Silage/ley crops (may be included and kept in storage to provide a feedstock for use to augment feed during winter seasons. Stored biomass is needed for times when the availability of other feed materials will be reduced)
• Other organic wastes available locally from other process industries.

* – When considering acceptance of some wastes, early thought should be given to the effects on the plant of Animal By-Products Regulations compliance, and necessary provision for handling and processing ABPR waste. ABPR applies to the EU states, but equivalent regulations should also be in force elsewhere. This is to avoid cross contamination health risks (eg Foot and Mouth disease).

[box type=”info” size=”large” style=”rounded” border=”full”]Extended List of Anaerobic Digestion Feedstocks Update[/box]

We recently held a session at which people suggested the following larger list feedstocks which can be used for fuelling biogas plants:

Anaerobic Digestion Plants can receive and treat the following types of anaerobic digestion feedstock:

– Fish oil
– Fish waste
– Dairy products
– Milk containing antibiotic residues
– Whey
– Concentrated whey
– Sewage sludge from wastewater treatment plants
– Grease sludge from foul water chambers, sewage sumps, pumping stations, grease traps etc
– Seaweed (but check salinity first)
– Animal feed waste/residues
– Flotation sludge
– Graded organic domestic waste
– Gastrointestinal contents from slaughterhouses
– Waste from slaughterhouses. Subject to regulatory requirements in-force: All category III types and category II types that have been sterilised at 133 degrees Celcius for 20 minutes.
– Pig/ livestock slaughterhouse blood
– Poultry – chopped – category III after sterilization
– Chicken waste/ feathers (Note: Chicken Litter can be troublesome due to its high ammonia content.)
– Eggs and egg waste products
– Sawdust from mink pelt processing
– Mink feed waste/residues
– Potatoes and potato pulp
– Coffee grinds, tea leaves etc
– Fruit, including residues from fruit processing
– Lemon peel, orange peel etc
– All cereal products
– Bakery waste – flour, bread and finished products
– Grass, maize – energy crops
– Ochre-rich water/ochre from wastewater treatment as long as there is a high organic content
– Waste from jam production
– Ices, ice-cream, all forms of ice-cream products
– Margarine, out of date butter, suet
– Waste from the production of soya oil and margarine
– Distillery waste
– Soft drinks and beer
– Brewer’s yeast
– Bleaching earth with high organic content
– Glycerine, including de-icing fluids from airports
– Coolants and antifreezes. For example, monoethylene glycol (blue coolant), organic acid coolant (green and red coolant)
– Sugar, molasses, etc.
– Drug residues from pharmaceutical companies
– Soap residues from soap manufacturers
– Past sell-by date food waste
– Household collection food waste
– Food products that have been bacteriologically or chemically contaminated
– Non-food organic/ vegetable/ putrescible products
– Catering and food processing factory waste
– Organic fraction of residudal wastes after processing of municipal solid waste in Mechanical Biological Treatment (MBT) Plants
– Manure and farming slurries

* Categories indicate requirements for prevention of the spread of disease. The requirements vary. Check these requirements with your local regulatory authority before use as anaerobic digestion feedstock.