Response of nitrogen transformation and microbial community to aromatic compounds stress along heterotrophic nitrification and aerobic denitrification process

Heterotrophic nitrification and aerobic denitrification (HNAD) process has received significant attention due to its ability to remove both nitrogen and refractory organics. However, the characteristics of nitrogen transformation and the response of microbial communities during HNAD process by aromatic pollutants remain unclear. Herein, we established the aerobic microcosms under the stress of aromatic pollutants by introducing aniline, trinitrotoluene and phenanthrene. Regular monitoring results showed that aromatic pollutants slightly inhibited the conversion of NH 4 + -N and NO 3 - -N within 36 h, and increased the transformation of inorganic to organic nitrogen during nitrogen removal. The final removal efficiencies for total nitrogen (TN) and chemical oxygen demand (COD) were not significantly affected and were as high as over 90%. Moreover, the introduction of aromatic pollutants reduced microbial diversity, causing microbes capable of removing nitrogen and aromatic compounds to gradually evolve into dominant genera, among which Aromatoleum , Acinetobacter , and Pseudomonas played a vital role. The co-occurrence network indicated that the stress of aromatic compounds increased the connectivity between microbes, and the relationships among microbes gradually shifted towards coexistence. Meanwhile, aromatic contaminants promoted biofilm formation and enhanced the environmental tolerance of microbial communities. Furthermore, the abundance of key genes IDH3 , sucD , sdhA/B , fumC , and mdh related to the carbon metabolism was inhibited in the microcosms containing aromatic pollutants, while the expression of key genes napA , nirS , and norB related to nitrogen metabolism was promoted. Our study provides guidance and deeper understanding for biological nitrogen removal in water bodies contaminated with aromatic compounds.