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 low-intensity aeration (1.0 L/(m(3)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. (c) 2005 Elsevier Ltd. All rights reserved.