Treatment of Fracturing Wastewater by Anaerobic Granular Sludge: The Effect of Salinity and its Mechanism

Abstract

The effects of salinity on the anaerobic treatment of fracturing wastewater regarding COD removal performance, sludge characteristics and microbial community were investigated. Results showed COD removal efficiency decreased from 76.0% to 69.1%, 65.6%, 33.7% and 21.9% with increasing salinity from control group (2.5 g/L) to 10, 15, 25 and 45 g/L, respectively. The cumulative biogas production decreased by 13.8%–81.1% when the salinity increased to 15–85 g/L. The increase of salinity led to the decline in the particle size of granular sludge, and the activity of granular sludge, including SMA, coenzyme F420 and dehydrogenase, was inhibited significantly. The results from flow cytometry indicated the percentage of damaged cells in granular sludge gradually increased with increase of salinity. Sequence analysis illustrated the microbial community structure in anaerobic digestion reactor was affected by the salinity, high salinity reduced the diversity of microbial community and decreased the abundance of methanogens, especially Methanosaeta.