Membrane contactors for the oxygen and pH control in desalination

The use of membrane contactors for the oxygen removal, as well as the pH control, in a reverse osmosis (RO) desalination plant was studied. Experimental tests were carried out in a lab set-up using a flat membrane module with 40 cm2 of membrane area, by feeding in a counter-current mode the liquid and a gas stream of CO2 or N2. Several operating conditions were varied, such as temperature, streams flow rates and liquid composition. The liquid streams sent to the system were distilled water and synthetic solutions (prepared for simulating the reverse osmosis permeate and brine and the nanofiltration permeate). Four different hydrophobic membranes (PVDF, PVDF-treated, acrylic-based, and PTFE membranes) were characterized in terms of water uptake, CAM and SEM analysis, tested in the membrane contactor and, finally, compared. Based on the experimental results, the application of membrane contactors for the pH adjustment in the pre-treatment line of a desalination plant when coagulation is used, was considered as case study.