Heat extraction and brine management from salinity gradient solar pond and membrane distillation

Abstract

The problem associated with the reverse osmosis (RO) system is its brine disposal. Experimental salinity gradient solar pond (SGSP) with surface area 4.65m2 was established to extract and apply heat on laboratory scale direct contact membrane distillation (DCMD). In this study, the performance of the SGSP and DCMD system under Pakistan’s climatic condition of Islamabad was evaluated. The heat extraction was carried out using internal heat exchanger by passing fresh water through it at different flow rates in summer and winter. Maximum temperature of 37°C in summer and 28.5°C in winter was extracted. The extracted heat from SGSP can be used to pre-heat the brine for temperature driven desalination processes. Least drop in lower convective zone (LCZ) temperature of SGSP was observed at flow rate of 7.5L/min. In DCMD, two temperatures obtained from SGSP (28.5 and 37°C) at feed side were maintained to investigate the permeate flux, percentage salt rejection and total dissolve solids (TDS). Two further temperatures 50 and 60°C were maintained to investigate the DCMD performance. Flux increased as temperature difference between feed and permeate increased. 28.5°C in terms of SGSP temperature was also feasible for DCMD process as flux was maintained over time.