Conversion of full nitritation to partial nitritation/anammox in a continuous granular reactor for low-strength ammonium wastewater treatment at 20 °C

The feasibility of converting full nitritation to partial nitritation/anammox (PN/A) at ambient temperature (20 degrees C) was investigated in a continuous granular reactor. The process was conducted without anammox bacteria inoculation for the treatment of 70 mg L-1 of low-strength ammonium nitrogen wastewater. Following the stepwise increase of the nitrogen loading rate from 0.84 to 1.30 kg N m(-3) d(-1) in 320 days of operation, the removal efficiency of total inorganic nitrogen (TIN) exceeded 80% under oxygen-limiting conditions. The mature PN/A granules, which had a compact structure and abundant biomass, exhibited a specific TIN removal rate of 0.11 g N g(-1) VSS d(-1) and a settling velocity of 70.2 m h(-1). This was comparable with that obtained at above 30 degrees C in previous reports. High-throughput pyrosequencing results revealed that the co-enrichment of aerobic and anaerobic ammonium-oxidizing bacteria identified as genera Nitrosomonas and Candidatus Kuenenia, which prompted a hybrid competition for oxygen and nitrite with nitrite-oxidizing bacteria (NOB). However, the overgrowth of novel NOB Candidatus Nitrotoga adapted to low temperatures and low nitrite concentration could potentially deteriorate the one-stage PN/A process by exhausting residual bulk ammonium under long-term excessive aeration.

Automated summary

The study found that converting full nitritation to partial nitritation/anammox at ambient temperature is feasible for treating low-strength ammonium nitrogen wastewater. High-throughput pyrosequencing results revealed the co-enrichment of different aerobic and anaerobic ammonium-oxidizing bacteria, which may potentially deteriorate the PN/A process.