Anaerobic digestion (or biogas technology) is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. It is a reliable technology for the treatment of wet, organic waste. Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat. Almost any organic material can be processed with anaerobic digestion.
A wide range of organic wastes are available in the Middle East for anaerobic digestion. In addition to MSW, large quantity of waste, in both solid and liquid forms, is generated by the industrial sector like sugar mills, agro=processing, food processing, leather, pharmaceuticals and paper and pulp industries. Poultry waste has the highest biogas potential per ton of waste, however livestock wastes have the greatest potential for energy generation in the agricultural sector.
Here is the list of potential feedstock for biogas production in the Middle East.
- Animal manure
- Energy crops
- Algal biomass
- Crop residues
- Organic fraction of MSW (OFMSW)
- Sewage sludge
- Grass clippings/garden waste
- Food residuals
- Institutional wastes etc.
- Food/beverage processing
- 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. 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 bio-waste, food leftovers, expired food, market wastes and crop residues).
It seems that AD is the most sustainable clean energy as its a positive energy process. Excellent article just to complete it by focusing on digestate important role as bio-fertilizer after biogas production, with very good and balanced nutriment composition Prof.Dr. Hassan EL Bari -University Ibn Tofail-Morocco