Impact of feedwater salinity on energy requirements of a small-scale membrane filtration system

Many remote communities in both developed and developing countries lack electricity and clean drinking water. One solution, for such communities that rely on brackish groundwater, is a photovoltaic (PV) powered hybrid ultrafiltration (UF)/nanofiltration (NF) or reverse osmosis (RO) membrane filtration system. The system prototype described here can produce between 150–280 L of clean water for each peak sunshine hour, depending on the salinity of the feedwater (1–5 g/L of total dissolved solids (TDS) ) and membrane choice. The best specific energy consumption (SEC) for achieving drinking water quality with a salinity of less than 0.5 g/L TDS from 1, 2.5 and 5 g/L salinity feedwater was 1.1, 1.8 and 2.6 kWh/m3, respectively. Slightly higher feedwaters (7.5 g/L) can be treated with one of the membranes tested, and as long as sufficient power is available for providing an adequate transmembrane pressure. Higher salinities cannot be treated effectively with the current system due to pressure limitations. Energy recovery would need to be investigated in order to achieve a competitive SEC for such high salinity feedwaters.