Advanced treatment of biologically treated coking wastewater by membrane distillation coupled with pre-coagulation

In this study, a laboratory-scale membrane distillation (MD) system was developed for advanced treatment of biologically treated coking wastewater (BTCW), while the effect of pre-coagulation was also investigated. Results showed that membrane distillation could effectively reject the salts (> 99.1%) and organic pollutants in BTCW (> 96.2%) and no membrane wetting was observed. The remaining organics in distillate was largely determined by the amount of volatile substances in the feed. Pre-coagulation with poly-aluminum chloride (PACl) was found to be effective for significantly reducing the contaminant level in BTCW. This in turn significantly reduces the propensity of membrane fouling. Use of polyacrylamide (PAM) as a coagulant aid could further decrease the contaminant level in BTCW, but it may lead to even severer membrane fouling. Scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and fluorescence spectra analyses revealed that the interaction between PACl and remaining organics could prevent the formation of calcium carbonate on the membrane surface, whereas the addition of PAM facilitated the accumulation of aggregates on membrane surface, leading to serious membrane fouling. This study shows that membrane distillation coupled with pre-coagulation could serve as a potential alternative for advanced treatment of biologically treated coking wastewater.