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Enhancement of Microbial Density and Methane Production in Advanced Anaerobic Digestion of Secondary Sewage Sludge by Continuous Removal of Ammonia

methane_production

Authors: Bing Tao, Joanne Donnelly, Ivo Oliveira, Ruth Anthony, Victoria Wilson, Sandra R. Esteves,

Keywords: Advanced anaerobic digestion; Ammonia inhibition; Ion-exchange resin; Zeolite; Thermal hydrolysed secondary sewage sludge; Bacteria and methanogens gene abundance

Abstract: Ammonia inhibition mitigation in anaerobic digestion of high solids content of thermally hydrolysed secondary sewage sludge by the NH4 + affinitive clinoptilolite and a strong acid type ion-exchange resin S957 was investigated. Continuous NH4 + -N removal was achieved through ion-exchanging at both temperatures with average removals of 50 and 70% for the clinoptilolite and resin dosed reactors, respectively. Approximate 0.2–0.5 unit of pH reduction was also observed in the dosed reactors. The synergy of NH4 + -N removal and pH reduction exponentially decreased free NH3 concentration, from 600 to 90 mg/ L at 43C, which mitigated ammonia inhibition and improved methane yields by approximately 54%. Microbial community profiling suggested that facilitated by ammonia removal, the improvement in methane production was mainly achieved through the doubling in bacterial density and a 6-fold increase in population of the Methanosarcinaceae family, which in turn improved the degradation of residual volatile fatty acids, proteins and carbohydrates.

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