Groundwater Treatment using the Fenton process: Changes in Natural OrganicMatter Characteristics and Arsenic Removal

This work investigates the use of Fenton’s process (pH 5.5 and 6; 0.10-0.50 mM Fe(II); molar ratios Fe(II) to H2O2 of 1:5-1:20) combined with flocculation for the treatment of groundwater which is rich in natural organic matter (NOM) (10.6±0.37 mg C/L) and arsenic (110±6.7 ?g/L). Changes to the character of the residual NOM fractions were followed, as well as the removal efficiencies of NOM and arsenic. Under optimal reaction conditions at pH 5.5, 55% of theDissolvedOrganic Carbon (DOC) was removed, whilst removals of specific disinfection by-product precursors of trihalomethanes (THM), haloacetic acids (HAA) and haloacetonitriles (HAN) were 80%, 75% and 98%, respectively. Total arsenic concentrations were reduced to below 5 ?g/L under all investigated experimental conditions. After the Fenton treatment, the percentage of the hydrophobic NOMfraction (humic acid and fulvic acid fraction) decreased, and the percentage of the hydrophilic fraction (acidic and non-acidic fractions) increased. The hydrophilic fraction, which was the most abundant in the treated water, was also the most reactive fraction towards THM and HAA formation, whereas the residual fulvic acid fraction contributed the most to the formation of HAN.