A reverse osmosis membrane is used to desalinate high salinity groundwater. It is proposed to build an RO plant that will process about 500,000 liters/day of saline feed water containing sodium chloride at a concentration of about 5,000 mg/L having osmotic pressure of 3.57 atm. The permeability of the membrane selected for desalting the above water source is 3.2x10-8 m3 water/(m2 •s•atm)..
1. If 50% of the feed is recovered as desalted water at observed salt rejection of ~99%.
a. What is the required minimum feed pressure assuming that the entire membrane surface is to produce water permeate.
b. Estimate the expected salt concentration of the concentrate stream?
c. Estimate the osmotic pressure of the exit concentrate stream?
d. What is the required membrane surface area?
2. If the concentration of the salt at the membrane surface, just at the exit end of the membrane channel, is a factor of 1.2 higher than the bulk concentration (assumed to be equal to the feed concentration), estimate the value of the mass transfer coefficient (in the appropriate units), assuming the same permeate flux as in part 91).