Impacts of nitrogen-containing coagulants on the nitritation/denitrification of anaerobic digester centrate

Abstract

Nitritation of anaerobic digestion centrate reduces aeration energy demand by preventing oxidation to nitrate and can be affected by changes in upstream processing of anaerobic digestate. Here we report autotrophic/heterotrophic nitritation and partial denitrification in a pilot-scale reactor treating anaerobic digester centrate amended with nitrogen-containing coagulants. The pilot reactor selected for a stable microbial community with nitritation of 60–65% of influent TKN; ∼30–35% nitrogen removal; low nitrate concentrations; and concurrent appearance of autotrophic and heterotrophic ammonia oxidizing bacteria (AOB). Dominant autotrophic AOB were Nitrosomonadaceae. Heterotrophic AOB included Xanthomonadaceae and Chitinophagaceae. Denitrifying bacteria included Comamonadaceae and Actinomycetales. The effects of coagulant dosage on nitritation were studied in bench-scale sequencing batch bioreactors (SBRs), where unclassified AOB were identified that had amoA sequences clustering between the autotrophic and heterotrophic clades. Heterotrophic nitritation was stimulated by glucose addition, especially in SBR biomass adapted to continuous coagulant addition, with elevated levels of Xanthomonadaceae, Chitinophagaceae, and Rhodanobacteraceae. Further research is needed to understand the effects of coagulants on downstream nitrogen removal unit operations and implications for land-application of treated biosolids.