Disposal of the waste sludge from activated sludge plant contributes about half of the total liquid waste treatment costs of the plant. A process is described which, applied to brewery/malting effluent, yields a dried sludge that has sufficient value as animal feed supplement to reduce overall effluent treatment costs. Combined brewery and maltings effluent receive activated sludge secondary treatment. The high BOD load and carbohydrate nature of the wastes produces a large amount of sludge (one pound per pound of BOD/1000 cu ft/day) that is difficult to settle and dewater. Treatment with cationic polyelectrolyte is followed by air flotation and the sludge is skimmed from the surface of the liquid. The separated sludge is then dried in a triple effect evaporator. Addition of 15 parts of oil (tallow or vegetable oil) to one part of sludge allows evaporation to dryness, the product being sludge solids suspended in oil. Finally, the oil is separated by centrifuge and the product passed through an expeller to reduce the residual oil content. The material produced is pleasant and easy to handle in bags or bulk. Analysis shows it to be rich in protein (45 to 50%) and a source of B vitamins. Its nutritional value is comparable to soya bean meal and extensive trials confirm its suitability for animal feed. The presence of 2 to 3 mg of vitamin B12 per lb qualifies it as Vitamin B12 supplement.
Keywords: brewing by-product effluent sediment