Rethinking water resources: Harnessing The Gambia River with pressure-driven membrane processes for sustainable supply

The Gambia River is a tidal and tropical river that covers 12 % of the area of The Gambia and is to date not harnessed for drinking water supply purposes. Previous investigation on water quality indicated that the upper regions, with permanent and pristine freshwater, would be well suited for drinking water supply. With seawater intrusion, however, the downstream tidal and saline region is expanding further inland, requiring desalination technologies. In the urban area near the river mouth, there is potential for water reuse, while addressing the increasing load of micropollutants (MPs) from the discharged wastewater effluents. Ultrafiltration (UF) could decrease the turbidity to ≤0.5 NTU with partial removal of dissolved organic carbon. During UF operation, transmembrane pressure increased due to fouling mainly caused by the high turbidity (up to 140 NTU) in the freshwater region. Nanofiltration/reverse osmosis (NF/RO) removed salinity and achieved the WHO recommendation for drinking water (< 1 g/L as TDS) in the tidal regions with salinities up to 4 g/L. MPs, with a total concentration of up to 26.3 μg/L for pesticides, 38.4 μg/L for pharmaceuticals, and 2.1 μg/L for hormones, were found in a wastewater treatment plant effluent discharged 500 m near the ocean. This led to water quality degradation of the nearby stream, connected to The Gambia River. NF/RO membranes were able to remove most of the MP to concentrations below the surface water guidelines. With an appropriate pretreatment to mitigate fouling, and thus reduce energy consumption and process overall cost, NF/RO technology is well suited for water supply from desalination of the tidal region of The Gambia River and municipal water reuse for non-potable purposes, such as irrigation.