Removal of dissolved organic matter fractions from reverse osmosis concentrate: comparing granular activated carbon and ion exchange resin adsorbents

Reverse osmosis (RO) generates a concentrate (ROC) containing dangerous levels of pollutants including dissolved organic carbon (DOC). Adsorption experiments were conducted to study the effectiveness of removing DOC and its fractions from ROCs produced in a water reclamation plant using three adsorbents tested individually and in sequential combination. The ROCs had 23-42 mg/L DOC which contained 83-90% hydrophilics. These hydrophilics comprised 72-76% humics, 2-3% biopolymers, 5-7% building blocks, and 16-18% low molecular weight neutrals. Granular activated carbon (GAC) removed a larger amount of DOC than two strong base anion exchange resins (Purolite A502PS, Purolite A860S). In both batch and column experiments, the adsorptive removal of the hydrophobic fraction was greater for GAC than for the Purolites. Humics present in hydrophilic fraction was completely removed by Purolites but only partially by GAC. In the sequential adsorption batch experiment, GAC followed by Purolite treatment removed more hydrophobics, however, Purolite followed by GAC removed more humics. Almost 100% of humics was removed for all doses of adsorbents when Purolite served as the first treatment. It is concluded that the order of adsorbent use for effectively treating ROC depends on the target DOC fraction intended to be removed.