Foaming control by automatic carbon source adjustment using an ORP profile in sequencing batch reactors for enhanced nitrogen removal in swine wastewater treatment

Incomplete denitrification and ammonia accumulation were found to cause proliferation of filamentous microorganisms in sequencing batch reactors (SBRs) for swine wastewater treatment. Foaming was observed in response to the accumulation of 115.2 and 12.2 mg/L of nitrate and ammonia, respectively. The mixed liquor suspended solids (MLSS) level in SBRs was decreased to 2,000 mg/L and the suspended solids in the effluent reached 200 mg/L when foaming appeared. However, the use of swine waste as an external carbon source for enhanced biological nitrogen removal was found to effectively control the foaming caused by filamentous microorganisms. Therefore, an optimum strategy for the addition of swine waste was designed using integrated real-time control to provide pulse input control of slurry based on the “nitrate knee” in the oxidation–reduction potential profile. In this case, the MLSS concentration was maintained at an average value of approximately 7,550 mg/L, while the SS in the effluent was less than 30 mg/L.