The influence of temperature on bioflocculation and settling of activated sludge and their flocculation mechanisms involved.

Effects of temperature (conventional (25 degrees C) vs. mesophilic (35 degrees C) vs. thermophilic (55 degrees C)) on activated sludge properties (production and composition of EPS and interaction potential) and their roles in bioflocculation and settling were studied using well-controlled sequencing batch reactors fed with a synthetic wastewater comprised of glucose and inorganic nutrients. The results show that thermophilic sludge had a poorer bioflocculation ability and settleability than that of conventional and mesophilic sludge. Analysis of extracellular polymeric substances (EPS) indicates that thermophilic sludge had a higher level of loosely bound EPS (LB-EPS) content than that of conventional and mesophilic sludge. The LB-EPS content of thermophilic sludge was ten times more than TB-EPS content of it, which coincided with higher supernatant turbidity. Therefore, the worse bioflocculation and settling ability of thermophilic sludge could be explained from the perspective of LB-EPS. Calculating the interaction energy of three kinds of sludge, the interaction barrier of thermophilic sludge disappeared which meant the attractive potential was dominant in the system. Thus, it should have led to a better flocculation, which did not agree with the actual performance. It indicates that the worse bioflocculation and settling ability of thermophilic sludge could be explained from the perspective of interaction energy.