Strategies to optimize a two-step fed sequencing batch reactor (SBR) system to remove nutrients from swine wastewater

Sequencing batch reactors are an effective technology to treat liquid waste for nitrogen and phosphorus removal, and their performance is largely affected by the feeding strategy and oxic/anoxic cycling. In this study, the effect of three operating parameters, i.e., the 1st/2nd volumetric feeding ratio (mL/mL), the 1st anaerobic/aerobic (An/Oxic) time ratio (min/min), and the 2nd An/Oxic time ratio (min/min), on the performance of a two-step fed sequencing batch reactor (SBR) system to treat swine wastewater for nutrients removal was examined. Central Composite Design and Response Surface Methodology were employed to test these parameters in order to optimize the removal efficiencies based on six response variables including total nitrogen (TN), ammonium nitrogen (NH4-N), total phosphorus (TP), dissolved phosphorus (DP), chemical oxygen demand (COD), and biochemical oxygen demand (BOD). The results showed that the three parameters had significant impact on all the response variables (TN, NH4-N, TP, DP, COD, and BOD), and the highest removal efficiency for each individual responses was associated with different combination of the three parameters. The maximum TN, NH4-N, TP, DP, COD, and BOD removal efficiencies obtained were 96.38%, 95.38%, 93.62%, 94.3%, 95.26%, and 92.84% at the optimal 1st/2nd volumetric feeding ratio, 1st An/Oxic time ratio, and 2nd An/Oxic time ratio of 3.23, 0.4, and 0.8 for TN; 2.64, 0.72, and 0.76 for NH4-N; 3.08, 1.16, and 1.07 for TP; 1.32, 0.81, and 1.0 for DP; 2.57, 0.96, and 1.12 for COD; and 1.62, 0.64, and 1.61 for BOD, respectively.