Effects of different electron donors on nitrogen removal performance and microbial community of denitrification system

Biological denitrification is an economical and effective process for the removal of NO3--N from wastewater. During the denitrification process, electron donors such as organic and inorganic compounds are required to provide electrons for the reduction of NO3--N. In this study, the effects of sulfide (sulfur autotrophic denitrification, stage I), sulfide and glucose (sulfur autotrophic-heterotrophic synergistic denitrification, stage II) and glucose (heterotrophic denitrification, stage III) on nitrogen removal performance and microbial characteristics of denitrification system were investigated. After adding 80 mg/L glucose in stage II, advanced nitrogen removal based on sulfur autotrophic and heterotrophic denitrification was achieved with a high NO3--N removal efficiency of 96.0%. The microbial species were marginally reduced as the denitrification system transitioned from sulfur autotrophic denitrification to heterotrophic denitrification, while the abundance of denitrifying bacteria grew dramatically. Comamonas, uncultured_bacterium_f_Burkholderiaceae and Enterobacter increased from less than 2% in stage I to 10.0%, 9.1% and 7.8% in stage III, respectively. In particular, the abundance of sulfur autotrophic denitrifying bacteria (Thiobacillus and Sulfurimonas) did not drop but somewhat increased in stage II. A potential interaction model between sulfur autotrophic and heterotrophic bacteria was proposed. The results of this study provide a novel idea and theoretical basis for improving the nitrogen removal efficiency of the system through biological enhancement or microbial community regulation.