Effects of External Carbon Sources on Ultimate Nitrogen Removal Performance and Microbial Community in Secondary Effluent Treating Process

Abstract

Adding external carbon sources is an important method for advanced nitrogen removal of secondary effluent in wastewater treatment plants (WWTPs). In order to compare the denitrification performance and economy of different carbon sources sufficiently, as well as the effect of long-term addition of carbon sources on the microbial population structure, four single carbon sources (methanol, ethanol, glucose, and sodium acetate) and four types of composite carbon sources were prepared by mixing sodium acetate and ethanol with a higher reaction rate and cheap glucose. The results showed that the effluent ρ(NOx--N) concentration of all systems was less than 1.0 mg·L-1 during the experiment. For single-carbon source systems, ethanol had the fastest denitrification rate, followed by sodium acetate and methanol; that of the glucose was the slowest. In the composite carbon source systems, the sodium acetate/glucose (1:1) with COD/ρ(N) was 6, which was equivalent to the results of sodium acetate/glucose (1:3), ethanol/glucose(1:1), and ethanol/glucose (1:3) with COD/ρ(N) of 9, 10, and 10, respectively. The sodium acetate/glucose (1:1) system had the fastest reaction rate and the best economy. High-throughput sequencing results showed that after more than 70 days of operation, the structure of the microbial community had changed completely. In the glucose-related system, the abundance of Candidatus Saccharibacteria, which is not popular in typical nitrogen removal systems, increased from 1.16% of seed sludge to 47.37%, and Saccharibacteria_genera_incertae_sedis correspondingly became the dominant community. This study not only provides a more comprehensive comparison for the selection of carbon sources in WWTPs with ultimate nitrogen removal but also provides basic data for the role of carbon sources in the domestication of microbial communities.