Insights into the one-stage DNRA-anammox reactors: Influence of carbon sources and C/N ratios

Abstract

Dissimilatory nitrate reduction to ammonia (DNRA) coupled with anammox has garnered attention due to its advantages over conventional denitrification in anammox processes. However, the mechanisms of organic matter type and the C/N ratio in regulating DNRA, denitrification, and consequently anammox performance remain unclear. To address the inquiries, two upflow anaerobic sludge blanket reactors were operated for 215 days to treat NO3 - using different carbon sources (acetate and glucose) at various C/N ratios. The removal efficiency of COD and nitrogen reached 79.0-80.1 % and 67.5-72.6 %, respectively, at C/N ratios of 0.2-0.3. The 15N-isotope pairing technique revealed that DNRA was the predominant NO3 -reduction pathway, with contribution of 86.2 % at a C/N ratio of 0.3 (glucose supply) and 85.2 % at a C/N ratio of 0.2 (acetate supply), surpassing denitrification or anammox. High-throughput 16S rRNA gene sequencing revealed Fimbriimonadales and Candidatus Jettenia as the predominant DNRA and anammox contributors. The elevated C/N ratio of 1.0 led to a notable proliferation of denitrifiers, eliminated DNRA and anammox bacteria, and substantially reduced COD and nitrogen removal efficiency. Lowering the C/N ratio to 0.5 marginally restored Fimbriimonadales and Candidatus Jettenia populations. Consequently, under both glucose and acetate addition, C/N ratios ranging 0.2-0.3 effectively formed a mutually beneficial relationship between DNRA bacteria (e.g., Fimbriimonadales) and AnAOB that can also perform DNRA (e.g., Candidatus Jettenia) possibly through cross-feeding of NO3 -and organic matter. This study indicates the viability of implementing one-stage DNRA-anammox system for simultaneously treating NO3 and COD in wastewater.