Effect of antiscalants and operating variables on the performance of desalination by direct contact membrane distillation (DCMD)

The effect of hydrodynamic conditions (feed and permeate flow rates) and of six different antiscalants was studied on the desalination of seawater from the Gulf of Mexico by direct contact membrane distillation (DCMD). The effect of feed temperature during the DCMD process was also evaluated on the performance of two microfiltration membranes (0.5 mu m) having a different thickness (300 and 250 mu m). Results showed more than 100% increments on water vapor flux by raising feed temperature from 50 to 70 oC and feed flow rates up to 7 L min(-1). No significant effect on process performance was observed by raising permeate flow rates in the range tested. However, process performance increased by up to 49.2% during the desalination of real seawater by adding the KMRO S-516 antiscalant, designed to disperse iron, silica, and calcium carbonate salts. Antiscalant dosage did not induce important water vapor flux decay or increase the conductivity of the distillate during DCMD. Scanning electron microscopy (SEM) from the membrane surface after DCMD desalination of seawater, treated with the KMRO S-516 antiscalant, evidenced the absence of scaling. Results from this work confirmed that the type and concentration of antiscalants are critical during seawater desalination by DCMD.