Bacterial community compositions of propylene oxide saponification wastewater treatment plants

The activated sludge process has been successfully used to treat propylene oxide (PO) saponification wastewater, which has the characteristics of high chlorine contents (22 000-26 000 mg L-1) and high COD (more than 2000 mg L-1). Microorganisms, especially bacteria, play an important role in PO saponification wastewater treatment processes. Analysis of the bacterial composition of the aeration tank and contact oxidation tank, the two main components of PO saponification wastewater treatment plants (SWWTP), revealed their significant community difference in municipal and coking wastewater treatment plants. Interestingly, beta-Proteobacteria was almost absent in the PO SWWTP, which was usually abundant in various bio-treatment systems. In the aeration tank of PO SWWTP, the most abundant genera were Marinobacter, Mesorhizobium, Paracoccus, Devosia, Methylophaga and KSA1. In the contact oxidation tank of PO SWWTP, the most abundant genera were Thalassospira, Marinobacter, Owenweeksia, Novispirillum, Mesorhizobium, Sporotomaculum, Pseudidiomarina and KSA1. We also measured the total components and toxicity of PO saponification wastewater in order to establish correlations between bacterial stains, genes and their treatment capacity. The results indicated that most of the bacteria encoded the dehalogenase gene and played an important role in the dechlorinating process of chlorinated organics in the aeration tank. In contrast, most of the bacteria encode the alkJ gene in the contact oxidation tank, which was involved in the degradation of 2,4-dimethyl-2-pentanol or some dechlorinated intermediate products. This study would provide new insight into the microbial community compositions of PO SWWTPs.