Treatment of liquid effluents from dairy cattle and pigs using reverse osmosis

As governments in Europe tighten the environmental regulations concerning husbandry due to air and water pollution from manure, an initiative has been taken in the search for improved techniques in the production, storage and spreading of manure. The possibility of reducing the volume of different types of animal waste waters by reverse osmosis was studied in a pilot plant. The volume reduction of waste water in cases where the urine had been collected separately in the shed and prevented from mixing with the faeces was 75-80%. The volume reduction of the liquid fraction of the slurry where the solid fraction had previously been removed with a screw separator or by sedimentation for at least 24 h was, despite the higher content of salts and dry matter, up to about 60%. The capacity of the equipment varied according to the degree of dilution of the waste water. Typically, fluxes in the range 20-25 l/m(2) h could be obtained at 30 bar and 25 degrees C. The retention in terms of chemical oxygen demand, and phosphorus was greater than 98% and, depending on the pH of the feed, 93-97% for ammonia. Reverse osmosis seems to be one possible way of decreasing the water content and hence the cost of storage, transport and spreading of manure without significant loss of nitrogen and phosphorous compounds. (C) 1999 Silsoe Research Institute.