Mass balance for a novel RO/FO hybrid system in seawater desalination

Seawater Reverse Osmosis (SWRO) desalination is being used by several countries to aid the current demand for fresh water, hence numerous large scale and small scale desalination plants have been built during last decade. Despite major advancements in SWRO technology, the desalination industry is still facing significant practical issues. Two of the major issues are (1) generation of higher volumes of pre-treatment sludge, and (2) overall water recovery. This paper proposes a novel hybrid reverse osmosis (RO) - forward osmosis (FO) system to overcome the above two drawbacks. Mass balance calculations based on laboratory experiments have been used to predict increased water recovery and reduced pre-treatment sludge volume arising from large scale (340,000 m3/day of intake) and small scale (15,000 m3/day of intake) hybrid SWRO desalination plants. The percentage reduction of pre-treatment sludge volume, increase in overall RO water recovery, FO membrane area required and dilution in RO reject have been estimated.