Microalgal-nitrifying bacterial consortium for energy-saving ammonia removal from anaerobic digestate of slaughterhouse wastewater

Abstract

Ammonia was removed from the anaerobic digestion effluent of slaughterhouse wastewater by a microalgal-nitrifying bacterial consortium under laboratory and ambient conditions. The highest ammonia removal of 80.4% with the lowest volatilization of 0.6% was achieved in the laboratory under half-day illuminated conditions at 140 μmol photons m−2 s-1 because a diel cycle could mitigate the light inhibition on nitrification and pH increase by photosynthesis. Nitrification was partially and completely inhibited by continuous illumination and sun-light, decreasing ammonia removal to 73.3% and 47.8%, respectively. Although the applied light intensities in this study were similar to or lower than those in previous studies, stronger nitrification inhibition was observed. Prolonged light exposure and/or high light intensity with excess free ammonia up to 59.4 mg L-1 probably inhibited nitrification; thus, light mitigation strategies, such as using granular sludge, will be effective when applying the consortium process under ambient conditions.