Abstract
The presence of geosmin in drinking water imparts a musty odour which leads to consumer complaints. Geosmin and other unwanted organics can be treated using photocatalysis. However, the intermediates formed during the photocatalytic degradation process and their degradation pathways have not previously been described. In this study, the degradation profile, as well as the intermediates formed during the photocatalytic degradation of geosmin was monitored in an effort to obtain a better understanding of the degradation kinetics and pathway. Photocatalytic degradation of geosmin in the presence of radical scavengers was shown to be inhibited, as evidenced by the reduction in reaction rate coefficient ( k’) from 0.055 to 0.038 min -1 . The hydroxyl radical reaction was thus shown to be the predominant process over direct photolysis by incident UV energy. Results from mass spectrum analysis of degradation intermediates indicate rapid fission of sp3─sp3 (C─C) bonds resulting in ring opening of the cyclic geosmin structure. Bicyclic compounds that could be expected from dehydration and dehydrogenation of geosmin’s ringed structure were not found among the detected intermediate products. Intermediates identified consisted of acyclic unsaturated alkenes, carbonyl compounds and some organic acids. Although the identified degradation products are not seen to be directly harmful, chlorine disinfection of water containing these compounds could produce potentially harmful halogenated hydrocarbons.
Highlights
Producing drinking water of good aesthetic quality is a major goal for all water authorities, mainly because consumers will judge suitability of the water based on its tactile quality
Large nutrient inputs from the above pollution sources have been associated with algal and cyanobacterial blooms in surface water bodies, which in turn result in the production of toxic organics and taste- and nuisance-causing compounds
The soil bacteria may be washed by rainfall runoff into nearby streams where they further increase the prevalence of odour-causing compounds in surface waters
Summary
Producing drinking water of good aesthetic quality is a major goal for all water authorities, mainly because consumers will judge suitability of the water based on its tactile quality (i.e., clarity, smell and taste). Good chemical quality is important beyond the water’s aesthetic quality This is because, at the present time, the majority of water resources – both surface water and groundwater – have been polluted with a variety of toxic and carcinogenic organic pollutants received from untreated or partially-treated domestic and industrial wastewaters and agricultural run-off (Griffini et al, 1999). Geosmin and 2-MIB impart taste and odour to water, thereby compromising the aesthetic quality of the water (Peter and Von Gunten, 2007). The presence of these compounds causes undesirable taint problems in the aquaculture industry. The soil bacteria may be washed by rainfall runoff into nearby streams where they further increase the prevalence of odour-causing compounds in surface waters
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