The effect of pretreatment and the operating temperature on reverse osmosis in make-up water preparation

Raw water cannot be used directly to compensate for water losses in power plants. Thus, a series of technological steps are required to produce ultra-pure water from fresh- or seawater. This study recommends using a proper pretreatment consisting of two-steps of microfiltration, ultrafiltration and nanofiltration. Desalination was carried out using two stages of reverse osmosis. The effect of increasing feed temperature from 25 °C to 48 °C on the second stage of reverse osmosis was studied and showed an exponential increase in flux and permeability, and reduced operation time. For freshwater, no temperature effect was observed on rejection in this temperature range; however, the highest rejection values calculated based on conductivity were observed at a 40 % recovery at all temperatures in seawater (96.6 % and 97.6 % at 48 and 25 °C, respectively). As a result of the multiparameter evaluation using the ranking method for the second reverse osmosis stage, 36 °C is found to be the optimum temperature.