Formation of hazardous by-products resulting from the irradiation of natural organic matter: Comparison between UV and VUV irradiation

The use of ultraviolet (UV) or vacuum ultraviolet (VUV) photo-oxidation followed by biological treatment for the removal of natural organic matter (NOM) in drinking water is a potential water treatment technique under investigation. This paper reports on the trihalomethane formation potential (THMFP), the haloacetic acid formation potential (HAAFP), and formation of nitrite and peroxide following both UV and VUV irradiation of NOM prior to biological treatment. The total THMFP was found to decrease with increasing UV and VUV irradiation dose, although there was a linear increase in bromoform formation. Determination of the THMFP of NOM fractions obtained after irradiation, showed that the hydrophobic fraction was dominated by chlorinated species which accounted for the majority of the total THMFP, while bromoform was observed only in the hydrophilic fraction of NOM. VUV irradiation reduced the HAAFP with increasing dose, in contrast, UV irradiation had a limited effect on the overall HAAFP. Following UV or VUV irradiation, the chlorinated species accounted for the majority of HAAFP; however, significant formation of brominated haloacetic acid (HAA) was observed. The nitrate concentration of the untreated water directly influenced the concentration of nitrite produced as a consequence of UV and VUV irradiation. Hydrogen peroxide formation was greater during VUV irradiation than during UV irradiation. Samples exposed to various doses of UV or VUV irradiation (up to 138 J cm−2) were deemed non-cytotoxic (African green monkey kidney cells) and non-mutagenic (Ames test).