The influence of different matrices on the nature and content of haloacetic acids precursors in ozonized water

Abstract

This paper investigates the influence of different matrices (groundwater - a realistic natural matrix and commercial humic acid solution - a synthetic matrix) on the nature and content of haloacetic acid (HAA) precursors in ozonized water (0.4 to 3.0 mg O 3/mg DOC; pH 6). Natural organic matter (NOM) characterization of the natural matrix showed it was largely of hydrophobic character (65% fulvic and 14% humic acids), with the hydrophilic fractions HPIA and HPI-NA at 12 and 9%, respectively. At approximately the same dissolved organic carbon (DOC) content of the investigated matrices (≈10 mg /L), a greater degree of hydrophobicity was seen in the humic acid solution than in the natural matrix, resulting in a higher content of HAA precursors (559±21 μg/L in the synthetic matrix compared to 309±15 μg/L in the natural matrix). By applying different ozone doses (0.4 to 3.0 mg O 3/mg DOC), the DOC content of the studied matrices was reduced by 6-22%, with a maximum process efficacy being achieved with 3.0 mg O 3/mg DOC. Ozonation also lead to changes in the NOM structure, i.e., complete oxidation of the humic acid fractions in both investigated matrices. After oxidation, hydrophilic structures dominate the natural water matrix (65%), whereas the synthetic matrix has an equal distribution of hydrophobic and hydrophilic fractions (~50%). Changes in the content and structure of NOM during ozonation resulted in the reduction of the total HAA precursors content (63-85%, using 3.0 mg O 3/mg DOC). Detailed analysis of the reactivity of the residual HAA precursor materials shows that ozonation using 3.0 mg O 3/mg DOC reduced the reactivity of the NOM fractions in comparison to the raw water. By contrast, HAA precursor material present in the commercial HA solution was transformed after ozonation into other reactive compounds, i.e., precursors which originated from the fulvic acid and hydrophilic fractions. The results of the laboratory testing indicate that the application of ozonation can reduce the content of haloacetic acid precursors to some degree. However, in real applications of oxidative treatment in the preparation of drinking water, as well as the efficacy in reducing the total organic matter content, the nature of the residual NOM must also be taken into account, as it can include toxic reactive precursors to disinfection byproducts.