Enhancement of sludge anaerobic digestion by using of a special thickening centrifuge

The intensification method of anaerobic methane fermentation of sludges, based on the stimulation activity of cell lysate, was studied. The effect of lysate is caused by the still remaining activity of released enzymes and by the stimulating properties of other compounds that are present inside the cells. The use of cell lysate as a stimulating agent was examined in the laboratory experiments of anaerobic degradation of municipal raw sludge, excess activated sludge and a mixture of them. The cell lysate was prepared by a partial mechanical destruction of cells of the excess activated sludge by a special adapted thickening centrifuge. The presence of aerobic cell lysate in thickened excess activated sludge causes a substantial increment in the methane yield and the biodegradability of thickened activated sludge in comparison with untreated excess sludge. The improvement of methane yield and biodegradability is influenced by the quality of input excess activated sludge and the parameters and efficiency of the thickening centrifuge. The improvement of methane yield from thickened activated sludge ranged from 8.1 to 86.4% dependent on the sludge quality. The improvement of methane yield from the mixture of thickened activated sludge and primary sludge ranged from 0 to 24%, and it was predominantly dependent on the fluctuating quality of primary sludge. The advantages of the stimulation method with the cell lysate are the following; the improvement of the anaerobic biodegradability of organic materials treated, the acceleration of the degradation process, the increment of methane production, the lowering of digested sludge amount and the improvement of the energetic balance of the process. (C) 1997 IAWQ. Published by Elsevier Science Ltd.