Fate of dissolved organic matter (DOM) in secondary effluent during granular activated carbon adsorption and soil aquifer treatment

In order to further removal the trihalomethanes precursors in reclaimed water during the secondary effluent reuse, the removal and transformation of dissolved organic matter (DOM) in secondary effluent during the granular activated carbon (GAC) adsorption and the laboratory-scale soil aquifer treatment (SAT) was studied. DOM was fractionated with XAD-8/XAD-4 resins into five classes: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The result showed that GAC was preferential in removing HPO-A, HPO-N and TPI-A. The high removal efficiency of HPI during the followed SAT treatment resulted in a higher DOM removal efficiency of 70.1% (which was only 42.1% during the GAC treatment). Up to a 73.1% reduction of THMFP (from 170.96 to 46.53 μg/L) was found for the bulk DOM during the SAT treatment, whereas only a 55.6% reduction occurred during the GAC treatment. The specific THMFP (STHMFP) of HPO-A, TPI-A and TPI-N were decreased efficiently during the GAC treatment, while that of the DOM fractions all showed a converse trend in the followed SAT treatment. HPO-A and HPI were the main THMs precursors of the secondary effluent. The GAC treatment was preferential in adsorbing more HPO-A, while the SAT treatment inclined to remove more HPI.