The treatment of flowback water in a sequencing batch reactor with aerobic granular sludge: Performance and microbial community structure

The extensive application of hydraulic fracturing technology has significantly promoted the large-scale development of shale gas. However, it is a great challenge for shale gas extraction to effectively manage large-volume flowback water (FW) with high salinity and complex organic substances. Here, we report an aerobic granular sludge (AGS) tolerable to high salinity, and suited to the treatment of FW. The performance of a sequencing batch reactor (SBR) with the AGS for the treatment of the synthetic FW and the microbial community structure at different salinity levels were investigated. The AGS fed with synthetic FW possessed a larger average particle size and a higher settling rate (50 m h−1). When NaCl concentration increased to 50.0 g L−1, the removal efficiency of total organic carbon (TOC) increased to 79 ± 1%, and the removal rate of polyacrylamide (PAM) raised up to 42.7 ± 0.7 g m−3 d−1. Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Sphingobacteriia dominated in the microbial community of AGS. Cellvibrionaceae, Rhodocyclaceae, Enterobacteriaceae, Moraxellaceae, Pseudomonadaceae, and Halomonadaceae belonging to Betaproteobacteria and Gammaproteobacteria played important role in degrading PAM, polycyclic aromatic hydrocarbons (PAH), and some other organics in FW at high salinity. These results suggest that an AGS-based SBR is a promising technology for the treatment of FW.