Abstract
The changes of nitrogen (NH4 +-N, NO2 −-N, and NO3 −-N), chemical oxygen demand (COD), dissolved phosphorus (DP), dissolved oxygen (DO), oxidization and reduction potential (ORP), and pH were tracked in a twice-fed sequencing batch reactor (SBR) treating swine wastewater at aeration intensities of 2.1, 4.2, and 6.3 L/m3 · s, with two alternating non-aeration/aeration phases. The SBR was fed at the beginning of each non-aeration phase with a volume ratio of 3:1. The results show that aeration intensity has positive effects on DO breakthrough and the maximum DO concentration during aeration. Additionally, nitrification, proceeding in an aerated environment with non-detectable DO, can be accelerated when aeration intensity increases from 2.1 to 4.2 L/m3 · s, while the COD and DP removals increase at the end of the aeration phase for higher aeration intensities (4.2 and 6.3 L/m3 · s). Online monitoring results indicate that pH is more sensitive than ORP in revealing the nitrification termination with non-detectable DO, whereas minimal ORP in the non-aeration phase has potential to be used as a control parameter for feeding.
Acknowledgments
The authors wish to thank the Minnesota Legislature Rapid Response fund and the Key Project of Science and Technology of Zhejiang Province (021103723) for funding this project.