Abstract
The effect of thermal pretreatment on the characteristics of degradation of waste activated sludge in anaerobic digestion was investigated using laboratory-scale batch and continuous experiments at 35±1°C. The pretreatment temperature of waste activated sludge ranged from 62 to 175°C and the holding time were 15, 30, 60 and 90 minutes.
organic solids were solubilizated to soluble proteins and carbohydrates or converted into lower molecular weight compounds such as volatile fatty acid by the thermal pretreatment. The anaerobic biodegradability and methane gas production was increased, and the retention time necessary for anaerobic digestion was possible to be reduced by lower than 10 days. The optimum pretreatment temperature and holding time for the upgrading of anaerobic digestion of waste activated sludge were 170°C and 60 minutes respectively. In this pretreament codition, at the retention time from 5.0 to 10.0 days, COD removal efficencies was about 60% and gas production ranged from 223 to 235 ml·gCOD-1, which was about 2 times that of the control. The rate of increase in solubilization and anaerobic degradation of major organic compounds in waste activated sludge with thermal pretreatment decreased in the following order : carbohydrate>protein>lipid. The number of total methanogenic bacteria existing at retention time from 1.5 to 10.0 days ranged from 107 to 108 MPN per ml of digester content.
