Membrane fouling alleviation by combination of sodium percarbonate oxidation and coagulation during microfiltration of shale gas produced water

Membrane fouling is the Achilles heel of membrane-based technologies. Severe membrane fouling occurs when a single microfiltration (MF) membrane is used to treat shale gas produced water (SGPW). Activated by Fe(II), sodium percarbonate (SPC) oxidation combined with aluminum sulfate coagulation was used in this study to evaluate the alleviation of MF fouling for the treatment of two typical SGPW samples with different water quality characteristics from Sichuan Basin. Results showed that pre-treated by oxidation and coagulation, more than 88% of turbidity, 11%–23% of UV₂₅₄, and 11%-36% of DOC were removed. With the increase in SPC dosage, there was a decrease in fluorescent organics, primarily reducing soluble microbial by-product-like components by up to 37.0% for sample 1 and aromatic protein and soluble microbial by-product-like components by up to 66.7% and 71.2% for sample 2, respectively. Compared to low normalized fluxes (2%-6%) for the raw SGPW, 61%-79% of normalized fluxes were obtained using the combination of 10 mmol/L SPC and 0.9 mmol/L Al₂(SO₄)₃·18H₂O. There was a general evolution of complete blocking to intermediate blocking or cake layer filtration for membrane fouling mechanism. Scanning electron microscopy observation, deposited foulants on membrane surface and Fourier transform infrared analysis further confirmed the superior performance of the combination of SPC oxidation and coagulation. Correlation analysis showed that UV₂₅₄ (R² = 0.79–0.95) played the most significant role in membrane fouling. Overall, this combined pretreatment process showed a great potential in MF membrane fouling control during the treatment of SGPW.