The ammonia nitrogen (NH4+-N) concentration in the effluent released from the secondary sedimentation tank of the original collagen enteric coating wastewater treatment process considerably exceeded the Chinese effluent discharge standard. Therefore, a one-stage simultaneous nitrification and denitrification coupled with the anaerobic ammonia oxidation (SNDA) process was designed to terminally treat collagen enteric coating wastewater containing low COD/NH4+-N (C/N). The entire process start-up and NH4+-N loading (NLR) domestication phase was completed within two months. During the NLR domestication, the NH4+-N removal rate was more than 90% and its effluent concentration was less than 15 mg/L, guaranteeing that the NH4+-N in the subsequent effluent was within the standard value. The results of microbial diversity show that Acinetobacter, Bacillus, and other heterotrophic nitrification-aerobic denitrification bacteria, and anammox ammonia oxidation bacteria were the main functional bacteria at the genus level, exhibiting high denitrification performance. The one-stage SNDA process effectively and stably removed nitrogen; the treated sewage satisfied the national comprehensive wastewater discharge standard (GB8978-1996), effectively saving 30-40% of the floor area and reducing 67.6% of the additionally added alkali, wherein the system's denitrifying bacteria compensated for some alkali consumed during the nitrification reaction.
Keywords: anaerobic ammoxidation; collagen casing wastewater; low C/N; simultaneous nitrification and denitrification.