Determine the Optimal ZLD Process for Reuse of Reverse Osmosis Effluent

Need for urban water supply in many parts of the world has become a crisis. The need for affordable inland desalination has become critical in many regions of the world where communities strive to meet rapidly growing water demands with limited freshwater supplies [1].
Among various desalination technologies, reverse osmosis (RO) membranes currently have wide acceptance [2].
In ZLD, concentrated water is treated to produce desalinated water and essentially dry salts. Consequently, there is no discharge of liquid waste from the process [3]. There are a variety of process options that can be considered for the intermediate concentrate step including adsorption processes, chemical precipitation, and ion exchange, or even combinations of these processes [4]. Water that passes through the membrane is recovered as product water. As recovery of product water in RO is pushed to its sustainable limit, water on the feed side of the membrane becomes increasingly concentrated and supersaturated, with respect to sparingly soluble salts such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), barium sulfate (BaSO4), and silica (SiO2) [5, 6, 7]. If the feed solution becomes sufficiently supersaturated, these salts precipitate and form deposits on the membrane surface. Deposition of these inorganic precipitates on the membrane surface, referred to as scaling, reduces the permeability of the membrane [8, 9]. Therefore, recovery in RO systems is limited by the precipitation potential of sparingly soluble salts [10].