Microbial structure and functions in the second aerobic bioreactor of O/H/O coking wastewater treatment system

Abstract:

[Background] The second aerobic bioreactor O₂ of the oxic-hydrolytic-oxic (O/H/O) system contributes to the biomineralization and complete nitrification of residual pollutants, which is important for the standard discharge of wastewater. [Objective] To elucidate the structure and functions of the microbial community in bioreactor O₂. [Methods] The 16S rRNA gene was sequenced to investigate the microbial diversity and composition, predict the microbial functional pathways, and reveal the microbial co-occurrence and the environmental driving factors in bioreactor O₂. [Results] Proteobacteria, Bacteroidetes, and Chlorobi were the dominant phyla in the bioreactor. Among the dominant genera, Rhodoplanes, Lysobacter, and Thiobacillus were involved in the degradation of residual pollutants, such as chemical oxygen demand (COD), phenols, and thiocyanate (SCN^-), and Nitrosovibrio and Nitrospira were the ammonia-oxidizing bacteria (AOB) and the dominant nitrite-oxidizing bacteria (NOB), respectively. Functional profiling suggested that the benzoate degradation, aminobenzoate degradation, chloroalkane and chloroalkene degradation, eluorobenzoate degradation, and nitrotoluene degradation were the top five pathways in the xenobiotics biodegradation and metabolism. These major functional pathways were distributed widely in the dominant genera, implying their roles in biodegradation of residual pollutants. The pmoA / B / C-amoA / B / C, hao, and nxrA / B encoding related enzymes constituted the nitrification pathway. According to the result of microbial co-occurrence network, Lysobacter, Candidatus Solibacter, and Rhodoplanes occupied an important position in the O₂ ecosystem. Redundancy analysis (RDA) suggested that the microbial community in the bioreactor was mainly affected by COD and NH₃ [Conclusion] Rhodoplanes and Lysobacter were the key genera for biomineralization and ecological stability of the community. Nitrosovibrio and Nitrospira played an important part in nitrification. The metabolic pathways in O₂ were dominated by biomineralization and complete nitrification of residual pollutants. COD and ammonia (NH₃) were the main influencing environmental factors. This study illustrates the structure and functions of microorganisms in bioreactor O₂, which is expected to lay a microbial basis for improving the treatment of coking wastewater by O/H/O system.

Key words:coking wastewater;aerobic bioreactor;high-throughput sequencing of 16S rRNA gene;microbial structure;functional profiling