Characteristics of a twice-fed sequencing batch reactor treating swine wastewater under control of aeration intensity.

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 x 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 x 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 x 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.