Enhanced biological nutrient removal in sequencing batch reactors operated as static/oxic/anoxic (SOA) process

An innovative static/oxic/anoxic (SOA) activated sludge process characterized by static phase as a substitute for conventional anaerobic stage was developed to enhance biological nutrient removal (BNR) with influent ammonia of 20 and 40 mg/L in R1 and R2 reactors, respectively. The results demonstrated that static phase could function as conventional anaerobic stage. In R1 lower influent ammonia concentration facilitated more polyphosphate accumulating organisms (PAOs) growth, but secondary phosphorus release occurred due to NOx- depletion during post-anoxic period. In R2, however, denitrifying phosphorus removal proceeded with sufficient NOx-. Both R1 and R2 saw simultaneous nitrification-denitrification. Glycogen was utilized to drive post-denitrification with denitrification rates in excess of typical endogenous decay rates. The anoxic stirring duration could be shortened from 3 to 1.5 h to avoid secondary phosphorus release in R1 and little adverse impact was found on nutrients removal in R2.