Nitrogen removal performance and influencing factors of in situ utilization of soluble microbial products (SMPs) by an anammox and denitrification immobilized filler coupling system

An anaerobic ammonia oxidation (anammox) and denitrifying immobilized filler coupling reactor (RAD) was established to systematically evaluate its performance for enhancing nitrogen removal using endogenous soluble microbial products (SMPs) in the absence of exogenous COD, and was compared with the coupling mode with exogenous COD addition. The results showed that compared with independent anammox reactor (RA), the RAD can effectively use SMPs to reduce the NO3--N yield and improve the total nitrogen removal efficiency. The NO3--N yield of the RAD decreased over time during the cycle, decreasing by up to 70% compared to the RA. 3D-excitation emission matrix showed that from the beginning to the end of the cycle, the SMP components changed from available tryptophan to difficult-to-use humic acids. In addition, the temperature and reaction cycle affected NOx--N transformation, while low temperature and a long cycle were not conducive to the complete reduction of NO3--N, leading to the accumulation of NO2--N. In contrast, adding exogenous COD accelerated NO3--N removal by the enhancing denitrification activity, but posed a potential threat to anammox activity. High-throughput sequencing analysis showed that Candidatus Kuenenia and Halomonas were the dominant species of the anammox and denitrifying immobilized fillers, respectively, which supported good coupling effect. These results provide valuable information for the optimization of anammox systems and the reduction of organic carbon consumption.

Automated summary

A RAD reactor was established to enhance nitrogen removal efficiency by using SMPs to reduce NO3--N yield, showing better performance compared to an independent anammox reactor. Temperature and reaction cycle affect NOx--N transformation, while adding exogenous COD can accelerate NO3--N removal.