The removal performance of nitrates in the novel 3D-BERS with GAC and diversity of immobilized microbial communities treating nitrate-polluted water: Effects of pH and COD/NO3--N ratio

In this work, a three-dimensional bioelectrochemical reactor system (3D-BERs) with granular activated carbon (GAC) was utilized to study the feasibility of simultaneous removal of nitrates by autotrophic-heterotrophic denitrification process under different pH levels. In this present study, it was found that when the influent COD/NO3--N ratio ranged between 1.5 and 3.5, both autotrophic and heterotrophic denitrifying microorganisms played an important role in denitrification The experimental results demonstrated that the highest removal efficiency of nitrates under the optimum COD/NO3--N ratio of 1.5 (98.62%) was achieved with an initial pH of 7.5 +/- 0.4. Likewise, when the COD/NO3--N ratio of 3.5, the nitrates removal efficiency (81.12%) was achieved with an initial pH of 8.2 +/- 0.3, respectively. Batch denitrification processes followed zero-order kinetics at various NO3--N concentrations obtained. The bacterial community structure and relative abundance of bacteria changed at the level of genes and the phylum of immobilized GAC particles. Moreover, the diversity of bacterial composition enhanced the removal of NO3--N at the inner surface (IS), and bottom surface (BS) of immobilized GAC carriers were Gammaproteobacteria, Bacilli, Proteobacteria, and Thauera. In general, this technique is more effective for enhancing the denitrification process in the 3D-BER system.

Automated summary

In this study, a three-dimensional bioelectrochemical reactor system (3D-BERs) with granular activated carbon (GAC) was used to investigate the simultaneous removal of nitrates through autotrophic-heterotrophic denitrification under different pH levels. The results showed that both autotrophic and heterotrophic denitrifying microorganisms played a crucial role in the denitrification process when the influent COD/NO3--N ratio ranged between 1.5 and 3.5. The highest removal efficiency of nitrates (98.62%) was achieved at an initial pH of 7.5 ± 0.4 with a COD/NO3--N ratio of 1.5, while an efficiency of 81.12% was achieved at an initial pH of 8.2 ± 0.3 with a COD/NO3--N ratio of 3.5. The bacterial community structure and diversity at the genetic level changed with the immobilized GAC particles, enabling enhanced removal of nitrates at different surfaces of the immobilized GAC carriers.