The Impact of UV/H₂O₂ Advanced Oxidation on Molecular Size Distribution of Chromophoric Natural Organic Matter

Abstract

The impact of hydroxyl radical (*OH) on the molecular weight distribution of natural organic matter (NOM) was investigated. *OH was generated via the photolysis of hydrogen peroxide (H2O2) by ultraviolet (UV) radiation of 254 nm, also known as UV/ H2O2 advanced oxidation (AO). Additionally, the impact of combined membrane and UV/H2O2 treatment on the molecular weight distribution of NOM was studied. High performance size exclusion chromatography (HPSEC) was used to determine the apparent molecular weight (AMW) distribution of chromophoric NOM (CNOM). Prior to AO, 33% of the CNOM in the water had AMW greater than 1400 Da. Meanwhile, lower AMW CNOM made up smaller amounts of the CNOM, with CNOM of AMW less than 450 Da making up 5% of the total. Under the AO conditions typically applied in drinking water treatment applications, NOM was not mineralized but was partially oxidized resulting in significant reduction in aromaticity. *OH preferentially reacted with higher AMW CNOM and the fragmentation of high AMW CNOM led to the formation of smaller AMW CNOM. Ultrafiltration removed all CNOM greater than 1400 Da AMW and a large portion of other high AMW fractions. In the absence of high AMW CNOM, *OH reacted more readily with all AMW fractions leading to a reduction in concentration of most AMW fractions. Whereas *OH reacted nonspecifically with all AMW fractions, the reaction rate between *OH and CNOM was observed to be dependent on molecular size.

Formation of aldehydes and carboxylic acids in ozonated surface water and wastewater: A clear relationship with fluorescence changes

“…The total amount of the carboxylic acids was about five times higher than that of the aldehydes, constituting a major fraction of newly formed AOC by ozonation. Similar observations have been made for experiments with other forms of advanced oxidation processes (AOPs) including O 3 /FeOOH (Zhang et al, 2008), O 3 /H 2 O 2 (Wert et al, 2007) and UV/H 2 O 2 treatment (Sarathy and Mohseni, 2007).…”

Degradation of natural organic matter in surface water using vacuum-UV irradiation

“…1b). After 180 min of irradiation, ␣ 254 decreased by 35% due to the breakdown of the chemical compounds, such as aromatic rings and double bond structures, responsible for absorbing radiation at 254 nm [17]. This observation was also supported by the HPSEC results, indicating changes in the apparent molecular weight distribution of organics (data not shown).…”

Photocatalytic degradation of methyl orange using polymer–titania microcomposites

“…It can involve the direct reaction of the dye with photogenerated holes in a process similar to the photo-Kolbe reaction or oxidation through successive attacks by hydroxyl radicals or superoxide species [41]. The hydroxy radical in particular is an extremely strong non-selective oxidant that has shown to lead to the partial or complete oxidation of many organic chemicals [42].…”