Effects of deoxygenation pretreatment and dissolved oxygen adjustment on performance of double-layer-packed sequencing biofilm batch reactor treating secondary effluent under low temperature

Abstract To meet the increasing stringent discharge standards, many wastewater treatment plants (WWTPs) are impelled to execute tertiary treatment, among which advanced nitrogen removal is still the key. An effective alternative for advanced nitrogen removal is sequencing biofilm batch reactor (SBBR), whose performance is closely related to dissolved oxygen (DO). In this study, the effects of deoxygenation pretreatment during anoxic phase and DO adjustment during aerobic phase on performance of double-layer-packed SBBR treating a typical carbon-lacked (COD/TN = 2.0, dominated with ammonium) secondary effluent under low temperature (15 °C) were investigated. It was found that deoxygenation pretreatment via adding sulfite had no significant impact on organics/phosphorus removal or nitrification but significantly improved denitrification. The deoxygenation stimulated nitrite accumulation leading to a higher simultaneous nitrification and denitrification (SND) rate. Similarly, with the increase of DO during aerobic phase, nitrification capacity increased while denitrification intensity decreased. When DO ≥ 3.5 mg/L, total ammonium nitrogen (TAN) in final effluent met the first A standard (GB 18918-2002, China). When DO at 2.5 mg/L, a highest denitrification intensity was observed while neither TAN nor total nitrogen (TN) in final effluent met the discharge standards probably mainly due to low temperature and carbon shortage. Among all the tests, FA and FNA were not the main causes for nitrite accumulation. The above findings might be helpful in guiding practical applications.