[Analysis of Respirogram Characteristics of Filamentous Bulking Caused by Low Dissolved Oxygen]

The current research on filamentous bulking focuses on the effluent quality and the settling properties but the reports on the microbial physiology under filamentous bulking conditions are seldom. In this study, the variations in the respirogram of microorganisms and affinity coefficient during filamentous bulking were explored in a sequence batch reactor. Low dissolved oxygen, regarded as the typical reason for filamentous bulking, was applied as the stimulation method. The results showed that microorganisms entered the physiological adaptation stage in the early period of low DO. The following properties were observed in the system:① a sudden increase in the endogenous specific oxygen uptake rate (SOUR_e) of activated sludge, ② an abrupt decrease in the specific oxygen uptake rate (SOUR_n) of autotrophic bacteria, ③ a rapid increase after a slight decline in the specific oxygen uptake rate (SOUR_c) of heterotrophic bacteria and a sudden increase in the oxygen affinity coefficient (KO). However, maintaining the low DO levels would deteriorate the effluent quality and sedimentation properties, but the SOUR_n and SOUR_c could recover to higher levels after a while and the COD affinity coefficient (KS) and KO would decrease gradually. In low DO conditions, a sufficient hydraulic retention time will benefit the effluent quality from a theoretical point of view. Moreover, microorganisms could adapt to low DO conditions, which verifies the feasibility of "low oxygen aeration theory" from the respiration and kinetic parameters. The results from this study provide a theoretical support for energy savings of sewage treatment plant operations.