Abstract:
The presence of natural organic matter (NOM) in groundwater could play an important role on removal of contaminants by nano-zero valent iron (NZVI). NOM has heterogeneous structure and could be divided into 6 fractions based on polarity and charges including hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral (HPIN). This study investigated the interaction between NOM fractions and NZVI using NOM surrogates. The reactivity between NZVI and NOM fractions isolated and bulk NOM from two sources including groundwater (GWNOM), Khon Kaen, Thailand and Suwannee River NOM (SRNOM), USA was also examined. The results showed that for NOM surrogates, humic acid (HPOA) had the highest interaction with NZVI while other NOM surrogates ((L-tryptophan, HPON), (aniline, HPOB), (oxalic acid, HPIA), (L-asparagine, HPIB), (D-xylose, HPIN)) had limited interactions. The Freundlich adsorption isotherm was found to fit the adsorption of HPOA and HPIA surrogates on NZVI. The results of fractionated NOM under various pH (5, 7, and 9) revealed that NOM fractions had more interaction with NZVI at pH 5 for both GWNOM and SRNOM. HPOA of GWNOM had the highest adsorption capacity (qe) of 6.95 mg/g while HPIN yielded the lowest qe (1.42 mg/g) at pH 5. For SRNOM, HPIA has the highest qe of 18.66 mg/g at pH 5 whereas the lowest qe of 1.45 mg/g was obtained from HPIN at pH 7. In addition, the effect of competitive interaction of NOM fractions was studied. HPOA was found to compete with HPON for GWNOM while HPOA remained the main fraction which reacted with NZVI for SRNOM. The findings of this study suggest that different components of NOM had different interactions with NZVI. Acid fractions tend to have more interaction than the other fractions. To apply NZVI for groundwater remediation, the composition of NOM should be considered to project the performance of NZVI for contaminant removals.
