Brackish Water Desalination using Reverse Osmosis

Abstract

Desalination of brackish water using Reverse Osmosis (RO) is carried out in this research to meet the National Drinking Water Quality Standards (NDWQS) of Pakistan i.e. < 1000 mg/L Total Dissolved Solids (TDS) concentration. Reverse Osmosis is a pressure driven, water treatment technology which uses a semi-permeable membrane to separate salts from water. After the design and installation of a Reverse Osmosis pilot plant, the system was operated on two commercial RO membranes (Filmtec® LCLE-4040 and Hydranautics® ESPA3-4040) to compare them on the basis of their treatment performance. The system was run for two hours on each membrane at six different TDS levels, from 2000 mg/L to 4500 mg/L, and at four recovery rates per TDS level. Results showed that upon increasing the recovery rates and TDS levels, there was a 2.57% decrease in salt rejection in Filmtec® membrane and a 9% decrease in Hydranautics® membrane. In terms of temperature, for Filmtec®, the salt passage increased at an average rate of 0.3% per degree rise in temperature, while for Hydranautics® the value was 0.96%. Moreover, with increasing recovery rates and TDS Levels, the pressure applied on membranes increases similarly. Lastly, no recordable trend was observed for the effect of pH on salt rejection. Based on the results, Filmtec® demonstrated a better performance in terms of salt rejection, stable operation and temperature tolerance, over a wide range of TDS levels and water recovery rates. To further optimize the operation of the unit, it is recommended to incorporate a temperature sensor and a controller in case over head tanks are used. Cartridge filters with a coarser size may be used to reduce the frequency of clogging. Finally, the system should be run on higher flowrates to improve the permeate quality.