Application of coagulation-UF hybrid process for shale gas fracturing flowback water recycling: Performance and fouling analysis

Shale gas fracturing flowback water (SGFFW) generated during shale gas extraction is of great concern and recycling for another fracking is the common disposal way. In this study, the feasibility of coagulation-UF hybrid process in assisting SGFFW reuse was systematically evaluated. Organics in SGFFW of Fuling were comparable with that reported in Marcellus. Poly aluminium chloride (PAC) dosage of 1500 mg/L may be preferred due to relatively low TOC (16.02 mg/L) and turbidity (3.03 NTU) in permeate and similar water flux (4.0x10(-4) m/s) with that under the dosage of 2000 mg/L. With increase dosage of PAC, fouling mechanism changed from complete blocking to intermediate-blocking or cake standard. SEM-EDS indicated foulant was rich in carbon and oxygen with iron oxide and sulfate precipitates. According to volumetric integration method, overall rejection ratio for organics in different region in hybrid process decreased in the order of V (89.0%), W 86.2%, III (80.3%), II (77.7%), I (55.2%) and VI (49.3%). LC-OCD illustrated coagulation mainly removed the organics with molecular weight of 20 kDa, while OF could remove a fraction of low molecular weight components (i.e., 200 Da). Fouling was reversible by backwashing and thus hybrid process without sedimentation can be potentially used for SGFFW treatment.