Separation of antiscalants from reverse osmosis concentrates using nanofiltration

One of the serious problems found in desalination using reverse osmosis (RO) is concentrate or brine management. This concentrate can actually be used as a raw material for salt production. However, antiscalants added during RO process should be removed before salt crystallization. This paper presents the separation of antiscalants from RO concentrate solution using nanofiltration (NF) membrane. Sodium hexametaphosphate (SHMP) and disodium ethylenediaminetetraacetate (Na2EDTA) were used as models of antiscalants. The effect of antiscalants concentration and addition of natural organic matters on both flux behavior and rejection were investigated. The results showed that the permeate flux behavior was influenced by the sodium chloride solution itself as a solution background, antiscalant type and antiscalant concentration. Osmotic pressure, concentration polarization and fouling or scaling contributed to flux decline during nanofiltration of antiscalants. NF membrane demonstrated very high rejection for both SHMP and Na2EDTA.