A simple approach has been implemented to identify the optimum RO (Reverse Osmosis) system structure and the operating parameters leading to the minimum total cost. Various two-stage and three-stage arrangements of practical functionality have been optimized. All possible operating points and its corresponding cost have been obtained and a linear search is used to find the minimum cost. The minimum overall costs per unit permeate for the single, two and three-stage arrangements are 1.41, 1.00 and 0.91 $/m3 respectively at product rates of 5.5, 11.5 and 17 m3/h.
For two-stage systems, parallel arrangement is recommended for production up to 3 m3/h. Series arrangement with feed and retentate bypass is recommended for demands between 3 and 9 m3/h. For higher permeate rates, series arrangement is recommended.
Using three-stage configuration, parallel arrangement is recommended for production less than 6 m3/h. Series arrangement with feed bypass is recommended for production up to 15 m3/h while series arrangement would be preferred above 15 m3/h.
Design charts have been developed as a convenient tool for selecting system configuration, operating parameters, membrane area and system cost. The use of design charts provides estimations of the system requirements and cost with about 5% accuracy without resorting to difficult computations.