Reasons and control measures for viscous bulking of activated sludge in A2O process

Abstract

Sludge viscosity expansion has always been a difficulty in the operation control of A2O process. The sludge viscosity expansion problem occurred in a sewage treatment plant in Zhengzhou City, resulting in poor sludge settling performance with SVI gradually increasing to about 240 mL/g and the mud level of the secondary sedimentation tank continuing to rise. The reasons of sludge swelling were analyzed from the aspects of inlet water quality, water temperature, aeration rate and scum. And then some measures such as adjusting the residual sludge discharge, sludge age, dissolved oxygen value, reflux ratio, hydraulic residence time were timely adopted, so that the sludge bulking problem was alleviated to a certain extent. In order to eliminate the floating mud in the biological tank, 40 mg/L cationic polymer flocculant was added to the distribution well of the secondary sedimentation tank. After a period of time, the sedimentation performance of the sludge was obviously improved with the SVI gradually decreasing to the normal level of about 120 mL/g, indicating that the problem of sludge viscosity swelling and eliminated the floating mud in the biological tank was solved. It provides a way to solve the viscous swelling of sludge.

Keywords

• a2o process
• sludge viscous bulking
• biological floating mud
• flocculant