Resource Base for Biogas Plants

Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. Almost any organic material can be processed with anaerobic digestion.

Anaerobic digestion is particularly suited to wet organic material and is commonly used for effluent and sewage treatment.  This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage and animal waste. Large quantity of waste, in both solid and liquid forms, is generated by the industrial sector like breweries, sugar mills, distilleries, food-processing industries, tanneries, and paper and pulp industries. Poultry waste has the highest per ton energy potential of electricity per ton but livestock have the greatest potential for energy generation in the agricultural sector.

Agricultural Feedstock

  • Animal manure
  • Energy crops
  • Algal biomass
  • Crop residues

Community-Based Feedstock

  • Organic fraction of MSW (OFMSW)
  • MSW
  • Sewage sludge
  • Grass clippings/garden waste
  • Food remains
  • Institutional wastes etc.

 Industrial Feedstock

  • Food/beverage processing
  • Dairy
  • Starch industry
  • Sugar industry
  • Pharmaceutical industry
  • Cosmetic industry
  • Biochemical industry
  • Pulp and paper
  • Slaughterhouse/rendering plant etc.

Anaerobic digestion is particularly suited to wet organic material and is commonly used for effluent and sewage treatment. Almost any organic material can be processed with anaerobic digestion process. This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage and animal waste. The exception to this is woody wastes that are largely unaffected by digestion as most anaerobic microorganisms are unable to degrade lignin.

Anaerobic digesters can also be fed with specially grown energy crops such as silage for dedicated biogas production. A wide range of crops, especially C-4 plants, demonstrate good biogas potentials. Corn is one of the most popular co-substrate in Germany while Sudan grass is grown as an energy crop for co-digestion in Austria. Crops like maize, sunflower, grass, beets etc., are finding increasing use in agricultural digesters as co-substrates as well as single substrate.

A wide range of organic substances are anaerobically easily degradable without major pretreatment. Among these are leachates, slops, sludges, oils, fats or whey. Some wastes can form inhibiting metabolites (e.g.NH3) during anaerobic digestion which require higher dilutions with substrates like manure or sewage sludge. A number of other waste materials often require pre-treatment steps (e.g. source separated municipal organic waste, food residuals, expired food, market wastes and crop residues).

Importance of Waste-to-Energy

Waste-to-energy has been evolving over the years and there are many new developments in this technology, moving in mainly one direction – to be able to applied to smaller size waste streams. Not only is it a strategy that has real importance for the current public policy, it is a strategy that will definitely present itself to additional areas.

More than 50% of waste that is burnt in waste-to-energy facilities is already part of the short carbon cycle. In which case, it has an organic derivative and it doesn’t add to climate change, to begin with. The long form carbon that is burned, things like plastics that have come out of the ground in the form of oil do add to climate change. But, they have already been used once. They have already been extracted once and what we are doing is taking the energy out of them after that physical use, capturing some of that (energy), thereby offsetting more carbon from natural gas or oil or coal. So, the net effect is a reduction in carbon emissions.

Waste-to-energy and recycling are complementary depending on the results of analyses of the First and Second Laws of Thermodynamics, which are absolutely valid. One can decide in specific situations whether waste-to-energy or whether some type of recycling technology would be more appropriate. It is not an either/or option.

In Austria, it was possible to have an absolute ban on landfilling wastes exceeding 5% organic carbon. This is written in law since 1996. There were some exceptions for some period of time, but landfills of organic wastes are just banned, not just in Austria but also in other cultures similar to Austria – like Switzerland and Germany.

Note: This excerpt is being published with the permission of our collaborative partner Be Waste Wise. The original excerpt and its video recording can be found at this link