Degradation mechanisms and byproducts formation of geosmin and 2-MIB during UV photolysis and combined UV/chlorine reaction

Abstract

The treatment and control of Geosmin (GSM) and 2-methylisoborneol (2-MIB) have become a priority task in the drinking water industry because these odorants have been associated with the quality and safety of drinking water. While the removals of common taste and odor (T&O) compounds by ozonation, ultrasonication and UV/AOP have been widely reported, only a little were reported on the formation of by-products during the treatment. GSM and 2-MIB have no health effect. However, these compounds have the possibility to be the precursors of THM as well as other hazardous by-products due to their strong oxidation potential. Therefore, the investigation of their by-products formed during treatmentis needed.In this study, chlorination, UV photolysis and combined UV/chlorine reactions were conducted to investigate the degradation mechanisms and byproducts formation of geosmin (GSM) and 2-methylisoborneol (2-MIB) in aqueous system. Chlorination was ineffective for the removal of GSM and 2-MIB, while UV irradiation and UV/chlorine reactions efficiently removed both compounds. Kinetics during UV photolysis and UV/chlorination followed the pseudo first-order reaction. Chloroform was found as a chlorinated byproduct during UV/chlorine reaction of both GSM and 2-MIB with the yield up to 87% while other chlorinated byproducts were not detected. The pH affected on both removal rate and chloroform production. The removal rate was highest at pH 5-7 and formation of chloroform was lowest at this condition. The byproducts of GSM and 2-MIB were identified by GC/MS and LC-MS/MS. The identified open ring and dehydration compounds were1,4-dimethyl-adamantane, 1,3-dimethyl-adamantane, 2-methylenebornane, 2-methyl-2-bornene, respectively. These byproducts were removed with further reaction. Furthermore, possible degradation pathways for the UV/Chlorine of both compounds were suggested.