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

• An Anammox-FBR was improved by small ring non-woven ring carriers.
• The total nitrogen loading reached 4.35 × 10−1 kg N m−3 d−1 on day 131.
• Low-oxygen adaptation was carried out by a stepwise increase of influent DO.
• The reactor performance was slightly affected after low-oxygen adaptation.
• A few AOB benefited reactor performance after introduction of influent DO.

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)2SO4 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 × 10−2 kg N m−3 d−1 and nitrogen removing rate (NRR) of 4.64 × 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 × 10−1 kg N m−3 d−1 and 3.83 × 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.