Application of Membrane Distillation for desalting brines from thermal desalination plants

Membrane Distillation (MD) is a hybrid thermal-membrane process that can use low grade waste heat to generate a vapor pressure difference across a hydrophobic membrane to produce a high quality distillate from concentrated brines. The MD process presents several benefits compared to Reverse Osmosis (RO) including: superior product water quality; ability to treat high salinity brines, and potentially lower capital & operating costs. These unique features of the MD process make it an ideal technical solution to desalinate brines from thermal desalination plants to increase fresh water production in the Arabian Gulf region.This paper evaluated the feasibility of using MD technology to desalinate brines from thermal desalination plants. A state-of-the-art MD bench scale unit was built and the performance of different MD membranes was compared under various operating conditions using synthetic saline solutions, brine from a thermal desalination plant and seawater from the Arabian Gulf. Overall, MD was shown to be a feasible and effective process capable of consistently producing high quality distillate (conductivity < 10 μS/cm) from high salinity brines (70,000 mg/l TDS) from a thermal desalination plant. A consortium consisting of the ConocoPhillips Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity & Water Company (QEWC) was formed to operate pilot-scale MD systems to desalinate brines from a full-scale thermal desalination plant in Qatar to determine process economics and address specific field conditions of the region.

► The feasibility of MD process to desalinate brine from thermal plants was evaluated.
► The MD process was capable of producing distillate quality water from thermal brine.
► The MD membrane flux was not affected by salt concentration from 0.1 to 70 g/l.
► Feed temperature and ΔT across the membrane have significant impact on MD production.
► Application of MD on seawater may require pH adjustment and/or antiscalants.