Enhancing the in-situ enrichment of anammox bacteria in aerobic granules to achieve high-rate CANON at low temperatures

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH4+ <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 2515 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008-0.013 d(-1) at 15 degrees C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N.m(-3).d(-1) and 68% treating low-strength ammonium (similar to 50 mg N.L-1) wastewater under such aggressive conditions (DO = 0.8-1.5 mg/L, HRT < 1.0 h, and T = 15 degrees C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study successfully started a high-rate CANON process by enhancing in-situ enrichment of anammox bacteria in aerobic granules. The dominant anammox species was Ca. Brocadia sapporoensis with an estimated growth rate of 0.008-0.013 d(-1) at 15 degrees C. The granular CANON process showed high total nitrogen removal rate and efficiency under aggressive conditions.