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.

In this study, a laboratory-scale partial nitrification reactor (PNR) was used to treat high-ammonia-nitrogen wastewater, with changing the influent NH4+-N load rate (INLR) as the main operating strategy, to investigate the upper limit of its NH4+-N load rate (NLR) and explore its use as an anammox pre-process. During the experiment, PNR was successfully activated in only ten days. The PNR reached the highest NLR value of approximately 9.79 kg N/(m3·d) when the INLR was 16.29 kg N/(m3·d), and the NH4+-N conversion rate (NCR) was 59.61% at this time. The value of [NO2--N]Eff/[NH4+-N]Eff was approximately 1.37. It is proved that it is feasible to use this PNR as a pre-process of anammox. The PCR-DGGE results showed that the dominant phylum and genus in the reactor during the INLR experiment were Proteobacteria and Nitrosomonas, respectively. With the increase in the INLR, the relative concentration of Nitrosomonas sp. G1 increased from 15–40%. This indicates that its abundance is directly correlated with the increase in the INLR. High-throughput sequencing showed that reducing the INLR of the PNR greatly reduced the diversity and abundance of the system microbial community structure and changed the dominant phylum and genus; however, the stability of the system was not disrupted. We hypothesize that the stability of the PNR mainly depended on the growth and changes of the functional bacteria in the reactor, and had little relationship with the diversity and abundance of the microbial community in the system.

No abstract

Anammox bacteria can remove ammonium directly, which is different from what was previously believed. This is an important process for the global nitrogen cycle. Anammox bacteria were first identified in sewage treatment systems and were later proven to exist widely in natural ecosystems. To better understand the relationship between the anammox reaction and different systems, and to maintain the stability of the nitrogen cycle, anammox functional microorganisms found in different natural environments were summarized. In addition, anammox nitrogen production rate and the contribution of anammox to nitrogen were discussed under different ecological environments. A literature analysis showed that the contribution rate of nitrogen removal of anammox was the highest in the Terrestrial ecosystem, up to 87.5%. The Terrestrial ecosystem is more likely to form an anoxic or even anaerobic environment conducive to anaerobic ammoxidation. Therefore, the control of DO is an important factor in the activity of anaerobic ammoxidation. Other environmental factors affecting the contribution of anammox to nitrogen removal include temperature, pH, organic matter content, inorganic nitrogen concentration, and salinity. However, the dominant influencing factors of anammox reactions in different ecosystems are evidently different. Therefore, the mechanism of the impact of different environmental factors on the anaerobic ammonia oxidation process is necessary to discuss. This provides a scientific basis for the global nitrogen cycle and is of great significance to improve nitrogen’s biogeochemical cycle in the ecosystem.