Efficiencies and mechanisms of the chemical cleaning of fouled polytetrafluoroethylene (PTFE) membranes during the microfiltration of alkali/surfactant/polymer flooding oilfield wastewater

The chemical cleaning of fouled polytetrafluoroethylene (PTFE) membranes with different reagents after the microfiltration of alkali/surfactant/polymer (ASP) flooding oilfield wastewater was examined in this study. Foulant analyses, cleaning efficiencies of different reagents and conditions and cleaning mechanisms were investigated. The results showed that anionic polyacrylamide (APAM) and crude oil were the main membrane foulants accompanied by organic–inorganic–organic/membrane aggregate foulants formed by bridging inorganic ions and organic species. Cleaning efficiency of 93% was acquired through mixed cleaning with 0.04 N NaClO + 200 mg L(−1) NaOH, which was found to be better than individual cleaning. Moreover, consecutive cleaning with NaClO + NaOH–HCl restored 98% of the membrane flux, suggesting that HCl cleaning contributed to flux recovery. Additionally, the cleaning temperature and time were set as 40 °C and 3 h, respectively, considering economy and membrane lifespan. Finally, the mechanism of membrane cleaning and analyses of membrane properties were described in this paper, aiming to provide a future direction for production practices. Considering that the cleaning reagents used in this study are easy to obtain and use, consecutive cleaning with NaClO + NaOH–HCl is recommended to clean the PTFE membranes fouled by ASP flooding oilfield wastewater.