Abstract: A bacterial strain with flocculation activity, which was screened in our laboratory, was used to examine the effects of duration of fermentation on flocculation. Results showed that when strain H5 (Acinetobacter baumannii strain) was used for fermentation for 36 h, the flocculation was 65.7%. he flocculating bacteria and polyaluminium chloride (PAC) were used to treat shale gas fracturing flowback fluid, and response surface methodology was used for optimization of the treatment process, using COD removal rate as the response variable. According to the distribution of response values, the optimal flocculation conditions were as follows:Addition of 10 mg/L of flocculating bacteria H5, PAC concentration of 30 mg/L, slow stirring speed of 73 r/min, and a sedimentation period of 40 minutes. Under optimal flocculation conditions, the COD removal rate was 85.1% and turbidity removal rate was more than 95.0% when combined treatment was used on shale gas fracturing fluids.

Key words: shale gas fracturing flowback fluid, flocculating bacteria, combined treatment, regression model, response surface methodology optimization