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 (N99.1%) and organic pollutants in BTCW (N96.2%) 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. © 2015 Elsevier B.V. All rights reserved.

This paper shows that membrane distillation could effectively reject the salts and organic pollutants in bio-treated coking wastewater without membrane wetting. The pre-coagulation with PACl and PAM aid was found to be effective for significantly reducing the pollutant level in biologically treated coking wastewater. The conductivity in distillate was maintained in a range of 25–60 μs/cm, and the remaining organics was largely determined by the amount of volatile substances in the feed. It was demonstrated that the pre-coagulation of BTCW by PACl could improve the permeate flux, whereas PAM aid might deteriorate the membrane performance. Membrane foulant analysis by FTIR and SEM–EDS indicates that organic fouling was found for all the samples, but calcium carbonates deposit is present only on the membrane surface when treating raw BTCW. PACl/PAM pre-coagulation leads to the concentration of humic-like and fulvic like substances, which could act as an Fig. 10. 3D-EEM results of DOM in the distillate and raw, pretreated BTCW samples. (a) Raw BTCW, (b) PACl-Tr BTCW, (c) PACl/PAM-Tr BTCW, (d) DCMD permeate of raw, (e) DCMD permeate of PACl-Tr and (f) DCMD permeate of PACl/PAM-Tr.