This study proposed a new method using freely available sunlight and granular activated carbon (GAC) adsorption for enhanced removal of humic substances (HS). Experiments were carried out under natural sunlight conditions in winter and summer. A parabolic solar collector (PC) was applied to concentrate solar energy. HS were characterized by UV254 absorbance, dissolved organic carbon (DOC) concentration and molecular weight (MW). As a result of solar irradiation, decreases of DOC up to 14% in winter and 58% in summer were observed. A comparison of adsorption isotherms and chromatograms of the irradiated and non-irradiated HS confirmed that smaller molecules formed during solar irradiation were preferentially adsorbed by GAC. A dramatic MW change upon solar irradiation was observed in HS irradiation in PC in summer experiment and almost no UV254 detected components were remaining in solution after adsorption (GAC dose 400 mg/L), as measured with high performance size exclusion chromatography (HPSEC). The combined solar irradiation-GAC adsorption method proved to be effective in enhancing HS removal by GAC with no additional energy and chemicals consumption.

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