EFFECTS OF THERMOCHEMICAL PRETREATMENT ON THE ANAEROBIC-DIGESTION OF WASTE ACTIVATED-SLUDGE

Effects of pretreatment on the anaerobic digestion of waste activated sludge (WAS) were investigated in terms of VSS solubilization and meth ane production by batch experiments. The methods of pretreatment studi ed are NaOH addition (chemical), heating (thermal) and heating with Na OH addition (thermochemical) to the domestic WAS and to the combined W AS from domestic, commercial and industrial wastewaters. The thermoche mical pretreatment gave the best result among three methods in the com bined WAS, i.e., the VSS was solubilized by 40-50% and the methane pro duction increased by more than 200% over the control when the WAS was heated at 130 degrees C for 5 minutes with the dose 0.3 g NaOH/g VSS. In the domestic WAS, the VSS solubilization rate was 70-80% but the in crease of the methane production was about 30% after thermochemically pretreated. The domestic WAS consists of 41% protein, 25% lipid and 14 % carbohydrate on COD basis, and the solubilization rate of protein, w hich is the largest constituent of the WAS, was 63% in the thermochemi cal pretreatment. Although the effect of the thermochemical pretreatme nt on the methane production was higher to the combined WAS than to th e domestic WAS, the methane production rate was 21.9 ml CH4/g VSS was . day in the domestic WAS and 12.8 ml CH4/g VSS was . day in the combi ned WAS. (C) 1997 IAWQ. Published by Elsevier Science Ltd.