Shortcut Nitrification and Denitrification of Swine Wastewater in a Sequencing Batch Reactor System

Abstract

Wastewater generated by confined swine production is characterized by high ammonium nitrogen (NH4 +-N) content, the elimination of which would require significant amounts of air in nitrification and organic carbon, serving as the electron donor, in denitrification. Shortcut nitrification and denitrification (SND) is a novel nitrogen removal process that has drawn researchers' attention lately. In this study, the application of SND in swine wastewater treatment was investigated using two sequencing batch reactors (SBRs) connected in series in order to reduce the needs for energy and carbon dosage. The first SBR produced a nitrite-rich effluent that was fed to the second SBR, where both nitrogen and phosphorus removal were achieved. Three COD/NOx-N ratios (3.6, 4.8, and 6) were selected to test the influence of carbon availability on the total inorganic nitrogen (TIN) reduction and phosphorus removal efficiencies for the second SBR. It was observed that COD/NOx-N ratios of 4.8 and 6 could achieve 97% and 98% TIN removals with effluents containing less than 20 mg L-1 TIN, while the 3.6 ratio resulted in only 84% removal, with a significant amount of nitrate accumulated in the system. The COD/NOx-N ratio had no significant influence on dissolved phosphorus (DP) removal, and the mean value of DP removal was about 52%. Two solid retention times (SRTs) were selected to test the effect of SRT on nitrogen and phosphorus removal. No significant difference in TIN removal was observed under SRT of 16 and 23 days, but DP removal was much better under SRT of 23 days than 16 days (around 67% vs. 38%). In conclusion, the introduction of SND to swine wastewater treatment obtained a satisfactory result for nitrogen removal but not for phosphorus under the current operational settings. Chemical precipitation may have to be used to further reduce phosphorus in the SBR effluent.