DEVELOPMENT OF A SIMULATION-MODEL PREDICTING PERFORMANCE OF REVERSE-OSMOSIS BATCH SYSTEMS

A model describing concentration profiles and performance relationships for the operation of a reverse osmosis system with a spiral-wound membrane module has been developed. The model is an enhancement of a previously proposed treatment and encompasses a discussion of mass transfer relationships and overall and component mass balances on a system operating in a closed-loop concentrating or recycling pattern. The presentation of mass transfer within a spiral wound membrane module is treated with an overall module approach with solution-diffusion mass transfer parameters empirically determined. A comparison with various methods to represent membrane feed side concentration and their effect on membrane performance is presented. A perspective is made on representing concentration polarization in this type of membrane configuration. The simulation model is verified with experimental data on simple aqueous salt systems. The simulations are excellent in predicting feed concentration profiles. Permeate flux deviates moderately and the permeate concentration only deviates significantly at high recoveries. A more exact depiction of the feed-side concentration improves the correlation to experimental data, but a more simplistic treatment may suffice under certain process conditions. The concentration polarization coefficient utilized was found to depend more heavily on the increase in flux due to a decrease in feed-side concentration rather than in the direct increase in feed concentration.