Comparison of performance and microbial communities in a bioelectrochemical system for simultaneous denitrification and chromium removal: Effects of pH

A novel bioelectrochemical system (BES) was established to investigate the feasibility of simultaneous autotrophic denitrification and chromium removal under different pH conditions in terms of the removal performance and dominant microbial community. Reliable nitrate and hexavalent chromium (Cr (VI)) removal was obtained, and the optimum pH was 7.0 with the highest removal efficiencies of 97.21 and 72.65%, respectively. The bacterial communities exhibited highly selective and concentrated as revealed by the alpha-diversity indices and the Pareto Lorenz (PL) evenness curves. The highest community richness was achieved under neutral environment, while increasing pH strengthen the species diversity. The predominant phylum Proteobacteria and class Gammaproteobacteria might act as the main contributors, accounting for 95.21-98.47% and 64.49-88.84% of the classified sequences. Key functional groups in terms of the denitrifying bacteria (DNB) and Cr reduction bacteria (CRB) were identified at the genus level. The similar total number of DNB and CRB indicated a good adaptability to pH. The stable removal ability was ascribed to the presences of Pseudomonas, Halomonas and Thauera, which facilitated the combined autohydrogenotrophic denitrification and Cr (VI) reduction process. This study provides a more in-depth understanding of application of BES for simultaneous denitrification and Cr (VI) reduction process.