A two-step fed SBR for treating swine manure

Specially designed sequencing batch reactors (SBR) may be a solution to disposal of massive pig manure, rich in nitrogen (N) and phosphorus (P), produced by concentrated swine operations. In this study, the technical feasibility of simultaneous N and P removals for swine manure was investigated through a bench-scale SBR system operated in a cyclic fashion of anaerobic–anoxic–anoxic/anaerobic–anoxic/aerobic using lowintensity aeration (1.0 L/(m s)), coupled with two-step influent feeding. The risks of emission of greenhouse gases (i.e., CH4, N2O and CO2) were also investigated during the critical periods of operation. 97.5% of the total nitrogen (TN) in the treated manure was removed with only 15 mg N/L of the oxidized N (NO3–N) left in the effluent. The reductions of total P (TP), chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD5), and turbidity reached 95, 96, 100, and 95%, respectively. The changes of nutrients as well as soluble COD over time in a complete cycle demonstrated that the SBR system could accomplish multiple processes featuring simultaneous nitrification–denitrification and P removal under aeration with undetectable dissolved oxygen (DO) in the liquid. The unique features of DO, oxidation–reduction potential (ORP) and pH tracked throughout the SBR operation reflected biological changes associated with the nutrients and organic matter in the manure. The primary influent feeding in 75% of the total amount, accompanied by a rapid drop in ORP, stimulated CH4 emission in a range from 990 to 1200 ppm; however, the secondary influent feeding in 25% of the total amount at the end of the first aeration, with combination of the previously accumulated NO2–N, resulted in N2O emission up to 13.9 ppm. # 2005 Elsevier Ltd. All rights reserved.