Enrichment of a denitratating microbial community through kinetic limitation
Matthew Baideme, Chenghua Long, Kartik Chandran
Abstract
Denitratation, or the intentionally engineered accumulation of nitrite (NO2–) from selective reduction of nitrate (NO3–), can be combined with downstream anammox to reduce chemical and energy use associated with conventional nitrification and denitrification. This study aimed to enrich a denitratating microbial community capable of significant NO2– accumulation by applying added kinetic limitation to an already stoichiometrically-limited, glycerol-driven denitratation process. Operation at solids residence time, SRT=3.0 d, resulted in optimal denitratation performance and a microbial community dominated by NO3–-respirers, noted by one order of magnitude lower total copy numbers of nirS and nirK gene transcripts compared to longer SRTs. Selective NO3– reduction to NO2– was achieved at all SRTs although longer SRTs (less kinetic limitation) supported microbial communities more capable of full denitrification as described by a lower NO2– accumulation ratio (NAR=42±5%) and higher steady-state nitrous oxide (1.5 mg/L N2O-N) accumulation. Shorter SRTs (more kinetic limitation) led to higher observed yields (Y=0.63 mg-COD/mg-COD) with more electrons dedicated for cell synthesis (fs=0.56±0.10), which potentially contributed to the accumulation of NO3–. Enrichment of a denitratating-dominant microbial community by optimizing kinetic limitation operating parameters could support significant NO2– accumulation and reduce chemical and energy use for biological nitrogen removal when combined with downstream anammox.