Low-ammonia wastewater treatment by integration of partial nitritation and anaerobic ammonium oxidation (anammox) at 20 ℃

Abstract

This study investigated a combined partial nitritation and anammox process for treating low-strength ammonia synthetic wastewater (~50 mg-NH4+-N/L) at 20 °C. The nitrifying bioreactor consisted of immobilized nitrifying bacteria in poly(vinyl alcohol) gel beads, which was operated under limited dissolved oxygen (DO) concentrations of 0.3–0.5 mg-O2/L to suppress nitrite-oxidizing bacteria (NOB) activity. The temperature in the nitrifying bioreactor decreased from 35 °C to 20 °C, and the hydraulic retention time (HRT) was shortened from 6 h to 3 h. The limited DO concentration enabled partial oxidation of ammonia to nitrite (55.8%), but an undesired nitrite oxidation rate of 31.5% was observed at 20 °C. The changes in bacterial community structure in response to the different operating conditions were observed by high-throughput 16S rRNA gene sequencing analysis. The lowered temperature resulted in a significant shift in the bacterial community structure, while the effect of HRT was negligible. Nitrosomonas ureae and Nitrospira moscoviensis played critical roles in nitrification at low DO concentrations. Interestingly, a high nitrogen-removal efficiency of 71.4% was achieved in the integrated nitrifying bioreactor and anammox at 20 °C despite incomplete NOB suppression in the nitrifying bioreactor. Denitratisoma oestradiolicum and Petrimonas sp., which are capable of nitrate reduction, were dominant in the anammox reactor, which might allow the provision of additional nitrite for the anammox reaction. The number of Candidatus Jettenia asiatica decreased in response to the lowered temperature, while the population of Candidatus Brocadia sinica increased.