FACTORS GOVERNING ODOROUS ALDEHYDE FORMATION AS DISINFECTION BY-PRODUCTS IN DRINKING WATER

摘要

Concern over disinfection by-products (DBPs) in drinking water has been focused on health risks with little attention to off-flavour consequences of disinfection. The discovery that odorous alde- hydes could be produced from the chlorination of common amino acids is a more recent concern. This research documents the yield of four odorous aldehydes produced from four common amino acids (iso- butyraldehyde from valine, isovaleraldehyde from leucine, 2-methylbutyraldehyde from isoleucine, phe- nylacetaldehyde from phenylalanine) from reactions with four common disinfectants, free chlorine. monochloramine, chlorine dioxide and ozone. Only free chlorine and monochloramine produced sub- stantial yields of the odorous aldehydes under conditions relevant to drinking water treatment. Factors affecting the aldehyde yield, including PH, temperature, reaction time and molar ratio (disinfectant/ amino acid precursor) were studied. The highest aldehyde yields were obtained with free chlorine, at op- timum conditions of PH 9, molar ratio l.5, reaction time 2 h and temperature 20.C. Slightly lower yields were observed at PH 7. These conditions produced maximum aldehyde yields ( of theoretical) for each amino acid precursor as follows isobutyraldehyde = 66, 2-methylbutyraldehyde = 74, isobutyraldehyde = 85 and phenylacetaldehyde = 87. Most observed aldehyde concentrations at maximum yields were in a range of maximum values (~50 mu g/l) reported in treated drinking water and well in excess of odour detection thresholds in water.