Integrated direct contact membrane distillation for olive mill wastewater treatment

Direct contact membrane distillation (DCMD) process was applied for olive mill wastewater (OMW) treatment and its concentration using a commercial flat-sheet polytetrafluoroethylene membrane (TF200, Gelman) with 0.2 μm mean pore size. The effects of the mean temperature and temperature difference on the DCMD permeate flux were studied. Two pre-treatment processes, coagulation/flocculation and microfiltration (MF), were considered and the effects of each one on the DCMD performance were investigated. MF was found to be the optimum pre-treatment to be integrated to DCMD for OMW. When the permeate temperature was kept constant at 20 °C, the DCMD permeate flux increased with the increase of the feed temperature. However, the permeate flux decreased with the feed phenol concentration of OMW. The concentration factor of each phenolic compound varied from 1.56 to 2.93. The main phenolic compound in the tested OMW samples was found to be the hydroxytyrosol, which was concentrated more than two times from 4.01 g/L to 8.16 g/L after 40 h of OMW processing by DCMD. The membrane fouling phenomenon was also studied. Results showed that the integrated MF/DCMD can be an effective process for the treatment and concentration of OMW obtaining clean water and a phenolic-rich concentrate.

Graphical abstractEvolution of the concentration factor, β, of OMW polyphenols in feed and the polyphenols separation coefficient, α, during Direct Contact Membrane Distillation (DCMD) for two different temperature conditions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► MF/DCMD was found to be an effective process for treatment and concentration of OMW. ► PTFE membrane exhibited reasonable permeate fluxes. ► PTFE membrane exhibited less than 35% water flux reduction rate (FR). ► Hydroxytyrosol was concentrated more than two times after 40 h OMW treatment by DCMD.