The biological reactions occurring during the digestion of organic matter in a biogas unit reduce the contents of waste materials by 30-60 per cent and produce stabilised product (slurry) which can be used as a fertiliser or soil conditioner.
Farmers use a lot of money to purchase inorganic fertilisers but owners of biogas plants can substitute, complement or replace the inorganic fertiliser with slurry.
This is because the organic matter is broken down to nitrogen, phosphorus and potassium (NPK), a common fertiliser in the market.
Slurry has gained momentum not only due to the search for organic fertilisers but also because of its twin benefit of providing fertiliser and water.
Slurry from the cattle dung is used as a fertiliser, generate algae in fish production, and manufacturing of animal feeds.
Slurry as fertiliser
Nitrogen from organic manure is extracted by bacteria from large organic molecules and transformed into smaller inorganic water soluble compounds.
This transformation is called mineralisation. During the digestion process in a biogas plant, part of the organic nitrogen is mineralised to ammonium and nitrate and thus may be taken up by the plants immediately. If ammonia is not dissolved in water it may escape as gas into the air.
Therefore, digested slurry has to be kept moist or covered b