Effects of activated sludge process conditions on the production of extracellular polymeric substances: Results of yearlong monitoring in a warm climate

Extracellular polymeric substances (EPS) play a key role in the activated sludge process (ASP) of wastewater treatment plants since they help bioflocculation thus influencing sedimentation and dewatering. Previous long-term studies have examined the effects of operating conditions on EPS in membrane bioreactors, while here we introduce a long-term study on activated sludge followed by gravity separation. To better understand the dynamics of EPS variation and composition in ASP, the present study focused on the effects of operating conditions as well as of seasonal environmental cycles on EPS at different sampling locations along activated sludge trains. Two ASP trains – one with full nitrification/denitrification with internal recirculation, and the other with partial nitrification/denitrification and no recirculation – were monitored for 13 months. Our results revealed that the ASP with internal recirculation had uniform EPS concentrations within the treatment train, whereas the process without internal recirculation exhibited a decreasing EPS trend along the treatment train. Concurrently, the EPS concentrations in both ASP trains did not exhibit seasonality. In other words, EPS production appeared process-dependent but not temperature-dependent. While the mean cell retention time of the activated sludge was shown to have no effect on EPS, the total inorganic nitrogen concentration from primary effluent was demonstrated to have a significant and direct relationship with EPS-protein and overall EPS production.