Factors governing odorous aldehyde formation as disinfection by-products in drinking water

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 aldehydes 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 (isobutyraldehyde from valine, isovaleraldehyde from leucine, 2-methylbutyraldehyde from isoleucine, phenylacetaldehyde from phenylalanine) from reactions with four common disinfectants, free chlorine, monochloramine, chlorine dioxide and ozone. Only free chlorine and monochloramine produced substantial 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 optimum conditions of pH 9, molar ratio 1.5, 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 μg/l) reported in treated drinking water and well in excess of odour detection thresholds in water.