Analysis and occurrence of odorous disinfection by-products from chlorination of amino acids in three different drinking water treatment plants and corresponding distribution networks.

Previous studies have established that odorous and stable chloraldimines are formed during amino acid chlorination in drinking water treatment. In order to identify at low level (10(-8) M) the presence of these odorous disinfection by-products in drinking water matrixes an analytical method was developed by using head space apparatus (HS) combined with a sorbent trap system linked to a GC with a mass spectrometer detector (HS/Trap/GC/MS). The analyses were carried out in three different drinking water supplies from the Paris area, during the four seasons. Free amino acids were monitored at the inlet of the plant. The odorous disinfection by-products were analyzed at the outlet of each drinking water treatment plant and the different distribution networks were connected to the corresponding plant. The results confirmed that the odorous chloraldimines are produced during chlorination of free amino acids in three different matrixes in different seasons throughout the year (N-chloroisobutaldimine; N-chloromethyl-2-butaldimine; N-chloromethyl-3-butaldimine (6-10 nM). The analytical method (HS/Trap/GC/MS) used to monitor odorous disinfection by-products appeared to be adapted for the detection of these by-products at nM level.

Impact of UV-irradiation on the formation of odorous chloroaldimines in drinking water.

In order to explain some of the possible origins of an odor episode which took place in a drinking water supply in the region of Paris (France), the impact of disinfection on the formation of odorous by-products was investigated. We have previously established that very odorous and stable chloroaldimines are formed during amino acid chlorination in conditions relevant to those of drinking water treatment. As chlorination is preceded by a UV-irradiation step, we examined here the impact of this irradiation on the formation of chloroaldimines. Irradiation (30 m W cm(-2)) of various amino acids (glycine, valine, phenylalanine) and peptides (Phe-Gly-Gly-Phe, Phe-Ala) led to a degradation of the compounds but it was negligible at the doses applied in drinking water supplies. As peptides were concerned, contrary to what we previously expected, the degradation did not involve the peptidic bond breaking: irradiation induces therefore no increase in the quantity of free amino acids, precursors of odorous chloroaldimines. However chlorination of peptides (Phe-Ala-Ala-Val, Phe-Gly-Gly-Phe and Ala-Phe) showed that chloroaldimines are also probably formed during combined amino acids chlorination.

Effect of chlorination on the formation of odorous disinfection by-products.

In order to explain some of the possible origins of an odor episode, which took place in a drinking water supply in the region of Paris (France), the chlorination reaction of some simple amino acids (valine, leucine and phenylalanine) was investigated. In addition to the commonly admitted intermediates and products of this reaction (monochloramines, aldehydes and nitriles), the formation of far less documented products was observed: N-chloroaldimines which proved to present particular properties. These products appeared to remain relatively stable in water, especially at low temperatures, and can be formed under disinfection conditions relevant to those of drinking water treatment (i.e. at high chlorination rates). N-chloroaldimines also present strong swimming pool odors with a floral background, with odor detection thresholds close to 1microgL(-1) and even less. These values were established with a laboratory-made protocol. These products appeared more odorous than the corresponding aldehydes, known for a long time as potent odor causing chemicals and which have previously been involved in some odor problems in the field of drinking water treatment. N-chloroaldimines are consequently products of interest for water treaters and are now suspected to be a source of off-flavor concerns among consumers. We have therefore developed an analytical method (gas chromatography coupled with mass spectrometry) to demonstrate the presence of some of these compounds in water at concentrations close to their odor detection thresholds. Considering the levels of amino acids that can be reached in water, this level of chloroaldimines concentration could be obtained under certain pollution conditions.