Respiration adaptation of activated sludge under dissolved oxygen and hypochlorite stressed conditions.

In this work, the relationship between environmental disturbance and the recovery of activated sludge at a low dissolved oxygen of 0.5mg/l or in the presence of sodium hypochlorite of 1-15mg Cl/gSS/d was examined. When microorganisms entered their physiological adaptation period, a sharp increase in endogenous respiration rate was observed. The activity recovery potential of sludge depended on the ratio of the endogenous respiration rate to the maximum respiration rate. A subsequent decrease in this ratio after a sharp increase indicates that the disturbance was recoverable. An increase in this ratio to a certain value, e.g., 0.35, suggests that the sludge system could not adapt to the new environments and thus was unrecoverable. In addition, the recoveries of sludge respiration and effluent quality were asynchronous, which was impacted by both sludge activity and operating conditions. These results provide a useful approach for the operation of activated sludge systems.