Division 4.7 Techniques for on farm manure processing

United Kingdom

Technique	Description
Mechanical separation of slurry.	Separation of liquid and solid fractions with different dry matter content, using e.g. screw press separators, decanter-centrifuge separators, separation by sieves and filter pressing. Separation can be enhanced by coagulation-flocculation of solid particles.
Anaerobic digestion of manure in a biogas installation.	Anaerobic microorganisms decompose the organic matter of manure in a closed reactor in the absence of oxygen. Biogas is produced and collected to serve energy generation i.e. production of heat, combined heat and power, and/or transport fuel. Some of the heat produced is recycled in the process. The stabilised residue (digestate) can be used as fertiliser (with sufficiently solid digestate after composting). Solid manure can be co-digested with slurry and/or other co-substrates, while ensuring a dry matter content lower than 12 %.
Use of an external tunnel for manure drying.	Manure is collected from the laying hen houses and removed by belts that convey it outdoors to a dedicated closed structure, containing a series of perforated overlapping belts that form the tunnel. Warm air is blown through the belts, drying the manure in about two or three days. The tunnel is ventilated with air extracted from the laying hens' house.
Aerobic digestion (aeration) of slurry.	The biological decomposition of organic matter under aerobic conditions. Stored slurry is aerated by means of submerged or floating aerators in a continuous or batch process. Operating variables are controlled to prevent nitrogen removal, such as keeping slurry agitation as low as possible. The residue can be used as fertiliser (composted or not) after concentration.
Nitrification-denitrification of slurry.	Part of the organic nitrogen is transformed into ammonium. Ammonium is oxidised by nitrifying bacteria into nitrite and nitrate. By applying anaerobic periods, the nitrate can be transformed into N₂ in the presence of organic carbon. In a secondary basin, the sludge settles, with part of it being reused in the aeration basin. The residue can be used as fertiliser (composted or not) after concentration.
Composting of solid manure.	The controlled aerobic decomposition of solid manure by microorganisms producing a final product (compost) sufficiently stable for transport, storage and landspreading. Odour, microbial pathogens and water content of manure are reduced. The solid fraction of the slurry can also be composted. The supply of oxygen is achieved by mechanical reversal of the windrows or by forced aeration of the heaps. Drums and composting tanks can also be used. Biological inoculum, green residues or other organic wastes (e.g. digestate) can be co-composted with solid manure.