Evaluation of direct contact membrane distillation coupled with fractionation and ozonation for the treatment of textile effluent

Abstract Direct contact membrane distillation (DCMD) coupled with fractionation or ozonation as a pretreatment method was investigated for the treatment of combined textile effluent. The stand-alone DCMD process has difficulty in directly treating the effluent due to the wetting issue, in particular at higher feed temperatures. Fractionation was conducted to 21 L combined effluent for 24 h. After the pretreatment, total organic carbon (TOC) and conductivity decreased by 47 % and 28 %, respectively, but an additional 5% concentrate was also generated. A long-term DCMD experiment was conducted to treat the fractionated effluent for 50 h and a high water recovery of 98 % was achieved. The optimum recovery of 95 % was identified to maintain stable performance of membrane. Ozonation was used to treat 550 mL combined eluent in batch mode. The TOC removal increased with time and reached the plateau after 1 min. The TOC was reduced by 38 %, while the colour of the combined effluent became lighter after 1 min treatment. As the temperature increased, longer ozonation time was required to inhibit the membrane wetting. For the feed inlet temperatures of 50 °C and 70 °C, the ozonation times of 40 s and 60 s were able to suppress the membrane wetting in the short-term tests. For the fractionated effluent, near zero discharge (water recovery of 98 %) could be achieved without serious wetting issue. To avoid membrane fouling issues, 95 % water recovery is recommended. For the 40 s ozonation pretreated effluent, DCMD could only achieve 38 % of the feed recovery before occurrence of wetting.