Treatment of greywater by forward osmosis technology: role of the operating temperature

Abstract

ABSTRACTEffects of operating conditions were investigated in terms of water flux, reverse salt flux (RSF) and pollutant rejection in a forward osmosis (FO) membrane system treating synthetic greywater. Changing cross-flow velocity had a slight impact on the performance of the FO membrane. Elevating operating temperature was more effective than increasing draw solution concentration to enhance the water flux. Further observation on the effect of heating mode showed that when the temperature was increased from 20 to 30°C, heating the feed solution (FS) side was better than heating the draw solution (DS) side or heating both sides; further increasing the temperature to 40 and 50°C, heating both the FS and DS achieved much higher water flux compared with only increasing the FS or DS temperature. Under isothermal conditions, a higher water flux and a lower RSF were achieved at 40°C than at other temperatures. Changing either FS or DS temperature had similar influences on water flux and RSF. The FO process revealed high rejection of nitrate (95.7%–100%), ammonia nitrogen (98.8%–100%), total nitrogen (97.4%–99.9%), linear alkylbenzene sulfonate (100%) and Mg (97.5%–100%). A mathematical model that could well simulate the water flux evolution in the present FO system was recommended.