The main steps in the treatment of fermentation residue substrates from biogas plants are: liquid - solid - matter separation, ultrafiltration using ceramic membranes and reverse osmosis. For the filtration of liquids will highly abrasive components - such as undis-solved macro-molecules in fermentation residue substrates - a highly abrasion - resistant membrane named Duratech has been developed. During fermen-tation only easily degradable organic matter is decomposed to methane and carbon dioxide leaving fermentation residue substrates which mainly consist of relatively stable organic substances that are more difficult to decompose. The nutrients contained in these resi-dues, such as organic nitrogen, potas-sium and phosphorus, are mineralized by the fermentation process. This means that fermentation residue sub-strates from biogas plants are an equivalent substitute for inorganic ferti-lizers, in particular because they can be spread on crop areas without the need for a lot of technical equipment, pene-trate the ground quickly and because their nutrients are available to the plants.
During the planning phase of the first reference plant built by A3-Water Solutions GmbH - which has a capacity of 64,000 liters per year and has been in operation for approximately 18 months - it was assumed that the costs for the treatment of fermentation residues including debt services would be EUR 5.10 per 1,000 kg. Already during the first year of operation opti-mizations in process engineering and an efficient operations management made it possible to remain under this amount. Treating fermentation residues produces a permeate with a high pure water quality and a solid and a liquid residue with the qualities of a valuable substance.