Degradation mechanism of two algal odorants, β-cyclocitral and β-ionone under UV photolysis, chlorination and UV-chlorination

Abstract

Algal taste and odor compound has become one of emerging concerns affecting drinking water quality. Among several algal odorants, β-cyclocitral and β-ionone are the oxidation byproducts of β-carotene existing in algae cells. Several AOPs such as UV-H2O2 and ozonation had adapted for algal odorants. However, degradation kinetic and byproducts of β-cyclocitral and β-ionone under UV-chlorination is not studied much. For these reasons, two odorants were treated by UV photolysis, chlorination and UV-chlorination and the degradation kinetic and byproducts of three treatment were examined. β-ionone showed faster degradation under all reactions compared to β-cyclocitral. The double bond on carbon chain of β-ionone is a reactive site for chlorination, hydroxyl radical attack and UV induced isomerization. Among three reaction, UV-chlorination was the most effective treatment due to generation of hydroxyl radical by reaction between UV and chlorine. Alkaline pH was not favored for UV-chlorination because hypochlorite is dominant form of active chlorine at alkaline pH and it is able to consume hydroxyl radical and it is inefficient for generating hydroxyl radical. During UV-chlorination reaction, only chloroform was generated for byproducts of reaction among regulated VOCs. It is due to methyl ketone functional group of the parent compounds. UV-chlorination had enhanced the formation of chloroform compared to chlorination. However increased amount of chloroform is very little compared to guideline limit. By GC-MS scanning, several intermediates of β-ionone under UV-chlorination were observed including β-cyclocitral. These compounds were formed by UV isomerization, hydroxyl radical attack and bond scission reaction.