Synoptic analysis of direct contact membrane distillation performance in Qatar: A case study

Abstract

The aim of this study is to evaluate a bench scale direct contact membrane distillation (DCMD) performance using flat sheet polytetrafluoroethylene (PTFE) membrane at different inlet flow rates, temperatures, and salinity composition. The effect of the various operating conditions on the quality of the distillate water produced was investigated by Inductively Coupled Plasma/Optical Emission Spectrometry (ICP/OES) and ion chromatography (IC). Five different feed solutions were studied such as the Arabian Gulf seawater, rejected brine from Qatari thermal desalination plants and artificial brine. A permeate flux of 35.6 LMH can be produced at temperature difference of 50. C between hot and cold sides. The thermal energy efficiency of the system was analyzed and reached up to 22%. The flow mode and turbulence promoter in feed channels were found to have a very important effect on the flux and energy efficiency. It was also noted that using spacers in the flow channels increase the distillate flux by more than 51% as compared with a spacer-free system. The investigation has shown that the highest Gain Output Ratio (GOR) value can be obtained when using less saline feed solution at the highest feed temperature, lowest permeate temperature and lowest flow rate. Finally, the salt rejection rate throughout the conducted tests was very high (>. 99.9%) and almost independent of any studied operational parameters. Eventually, DCMD has proven to be a feasible and effective technology capable of consistently producing high quality distillate from a very high salinity feed even with substantial quality difference compared to other desalination methods such as RO and MSF.