SOC Removal in a Membrane Softening Process

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Abstract
The authors investigated the rejection of six synthetic organic chemicals (SOCs) in a potable water source by a nanofiltration membrane softening process. Each SOC was studied separately for one month—which was subdivided into four recovery periods. The four largest‐molecular‐weight compounds (chlordane, heptachlor, methoxychlor, and alachlor) were completely rejected by the membrane. Ethylene dibromide, the lowest‐molecular‐weight compound studied, was not rejected by the membrane, whereas dibromochloropropane was partially rejected. Mass balances indicated that SOC recovery decreased as SOC molecular weight (MW) increased, which suggested that the three largest‐MW SOCs had been adsorbed by the membrane. The percentage of SOC rejection increased as MW increased, and the rejection of inorganic solutes increased as MW and species charge increased. No effect on solute mass transfer of any solutes resulted from membrane feed‐stream velocities, which were estimated to vary from 0.19 to 0.52 fps.

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