Cascade anaerobic digestion system treating waste activated sludge under short sludge retention time: process performance and role of recirculation

Hydrolysis, where the complex insoluble organic matter is hydrolyzed by hydrolytic enzymes, is regarded as rate-limiting step for anaerobic digestion of waste activated sludge (WAS). The cascade system, which consisted of small-reactors in series, was developed in this study to enhance the hydrolysis rate. Degradation efficiency of sludge was...