Insights into bacterial diversity in industrial post-processing water from underground coal gasification (UCG) process

This study represents the first culture-independent profiling of microbial diversity in post-processing wastewater from underground coal gasification (UCG) processes. Three types of post-processing wastewater, named W1, W2 and W3, were obtained from three UCG processes involving two types of coal and two gasification agents, namely oxygen-enriched air and oxygen. Very high concentrations of BTEX (benzene, toluene, ethylbenzene, xylene), polyaromatic hydrocarbons (PAHs), and phenol were detected in the wastewater, classifying it into the fifth toxicity class, indicating very high acute toxicity. The values for the Shannon (H), Ace and Chao1 indices in W2 were the lowest compared to their values in W1 and W3. The dominate phyla were Proteobacteria, contributing 84.64% and 77.92% in W1 and W3, respectively, while Firmicutes dominated in W2 with a contribution of 66.85%. At the class level, Gammaproteobacteria and Alphaproteobacteria were predominant in W1 and W3, while Bacilli and Actinobacteria were predominant in W2. Among Bacilli, the Paenibacillus and Bacillus genera were the most numerous. Our results suggest that the main differentiating factor of the bacterial structure and diversity in the wastewater could be the gasification agent. These findings provide new insights into the shifting patterns of dominant bacteria in post-processing wastewater and illustrate the spread of bacteria in industrial contaminated wastewater.