NUTRIENT REMOVAL AND NITROUS OXIDE EMISSION BY A TWO-STEP FED SBR IN TREATING DAIRY MANURE WASTEWATER

摘要

In this study, a two-step fed sequencing batch reactor (SBR) was employed to treat dairy manure wastewater to remove nutrients, including nitrogen, phosphorus, 5-day biochemical oxygen demand (BOD5), and chemical oxygen demand (COD), and to examine the associated nitrous oxide (N2O) emission by the SBR treatment. The SBR was operated on an 8 h cycle with preset time periods for different phases, including anoxic/anaerobic/aerobic phases. The results showed that the SBR system could effectively reduce the nutrients in the wastewater, with removal efficiencies reaching 86.6%, 95.6%, 98.8%, 100%, 97.9%, 95.6%, and 99.8%, respectively, for volatile solids (VS), volatile suspended solids (VSS), total Kjeldahl nitrogen (TKN), ammonium nitrogen (NH4+-N), total phosphorus (TP), COD, and BOD5. However, the SBR could not complete denitrification at the end of the cycle, with 12 mg L-1 nitrate left in the effluent, possibly due to suppression of denitrifiers by the anoxic/aeration phase that was placed almost at the end of cycle and overprovided oxygen to the liquid. Denitrification was found to be a major process for N2O generation, so reducing denitrification time in the cycle is recommended, given that the overall performance of the SBR system in removing nutrients was not compromised. Using oxidationreduction potential (ORP) alone to automate the SBR control was not sufficient to avoid failure of the system.