Performance of Anammox process and low-oxygen adaptability of Anammox biofilms in a FBR with small ring non-woven carriers

Performance of Anammox process and low-oxygen adaptation of the cultivated Anammox biofilms were investigated in a lab-scale fixed-bed reactor filled with small ring non-woven carriers. (NH4)(2)SO4 and NaNO2 provided NH4+-N and NO2--N in the synthetic wastewater. Anammox reaction occurred on day 17. After 67 days operation, start-up of Anammox was achieved with a total nitrogen loading rate (NLR) of 5.78 x 10(-2) kg N m(-3) d(-1) and nitrogen removing rate (NRR) of 4.64 x 10(-2) kg N m(-3) d(-1) on day 131. Under the strict anaerobic condition, the max total NLR and NRR reached 4.35 x 10(-1) kg N m(-3) d(-1) and 3.83 x 10(-1) kg N m(-3) d(-1). Subsequently, a stepwise oxygen adaptation strategy was applied by increasing influent dissolved oxygen (DO) to 8 mg L-1 with each increment of 2 mg L-1. The Anammox biofilms manifested a satisfactory oxygen adaptability. The reactor performance was only slightly affected as the average total NLR and NRR decreased by 7.08% and 4.39% respectively. Fluorescent in situ hybridization analysis further confirmed that, after low-oxygen adaptation, Anammox bacteria occupied 70.2% of the total bacteria and aerobic ammonium oxidizers moderately increased to 8.5%, which could alleviate the impact of influent DO on the reactor performance. Utilization of the low-oxygen adaptability of Anammox biofilms can markedly reduce energy and material consumption of Anammox operation. (C) 2015 Elsevier B.V. All rights reserved.