It is required to design an ro module for production of 2500 mº/day potable water containing not more than 250 ppm salt from sea water containing 44 g salt per litre. a proprietary asymmetric cellulose acetate membrane with an inherent salt rejection ability of 98% is to be used. the water permeation coefficient is 0.045 m²/m² day. atm. the recovery of the feed water should be 35% and an operating pressure of 70 atm gauge is suggested. the permeate side is at essentially atmospheric pressure. if spiral wound modules of 5 m² effective membrane area each is used, how many modules in parallel are required? what fraction of the input power can be recovered from the retentate if a turbine of 70% efficiency is used for energy recovery? the osmotic pressure of 5% brine (linear in salt concentration) is 39.5 atm