Effect of Alkaline Pre-Treatment on Waste Activated Sludge Solubilization and Anaerobic Digestion

In order to enhance the efficiency of anaerobic digestion, the effect of alkaline pre-treatment has been studied on waste activated sludge(WAS) from a wastewater treatment plant(WWTP) in Shanghai, China. The results indicated that sodium hydroxide strongly influenced the solubilization of sludge and subsequent anaerobic digestion. The COD and protein solubilization was most effective when sludge was pretreated at high pH value. At pH=12, COD solubilization achieved about 50%, which induced 40 times increase in SCOD from 200 mg/l to 8000 mg/l. But at low pH(pH les9), the degree of COD and protein solubilization was not significant. The subsequent anaerobic digestion was also improved by alkaline pre-treatment. WAS at higher pH resulted in a better removal of COD, further degradation of VS and larger production of methane. However, in the beginning of anaerobic digestion under condition pH=12, a inhibition period of one week occurred. Possible mechanisms of alkaline pre-treatment were also discussed.