Membrane distillation treating a real petrochemical reverse osmosis concentrate: Influence of membrane characteristics on the process performance

The present study investigated the applicability of direct contact membrane distillation (DCMD) in the treatment of a reverse osmosis concentrate (ROC) from petrochemical wastewater. Three commercial flat sheet membranes made of polyethylene or polytetrafluoroethylene, having different contact angles, pore sizes, porosities, and thicknesses, were supplied by Aquastill with the following membrane designation: Standard, Oleophobic and Teflon. Firstly, the different DCMD membranes were characterised in experiments with deionised water. Then, tests with ROC, with a temperature setting to 60 °C in the feed and 20 °C on the distillate side, were performed in full recirculation mode (along 250 h operating time) and in concentration mode (along 72 h operating time, achieving volumetric concentration factors around 10). The DCMD performance, in terms of flux and quality of the distillate, was evaluated during all experiments under different operating conditions. After obtaining the results, all membranes satisfactorily achieved a final water recovery ratio close to 90 %, as well as high rejection factors (above 99.5 %) for all parameters analysed. They also produced high quality water with low electrical conductivity (around 2–7 μS cm–1). All conditions met the requirements for water reuse in the petrochemical sector. In this case, to treat wastewater with the tested characteristics, the oleophobic membrane from Aquastill presented better efficiency, with a minimum water vapour flux reduction and a water recovery ratio of 90 %.