UV dechloramination has become a very popular process for reducing the concentration of chloramines in public swimming pool water. As the effects of this process on the formation of disinfection byproducts (DBPs) remain a controversial issue, a bench-scale study has been undertaken to examine the impact of UV dechloramination on the formation of various DBPs. Four pool water samples were exposed to UV radiation at 254 nm in the presence of free chlorine ([Cl 2 ] 0 = 3 mg L-1) and then chlorinated in the dark for 24 h ([Cl 2 ] 0 = 3 mg L-1). High UV doses (up to 47 kJ m-2) were used to simulate cumulative UV doses received by real pool waters. The data showed that UV irradiation led to a 90 % photodecay of free chlorine for UV doses ranging from 13 to 20 kJ m-2 , to the formation of chlorate ion (0.05-0.11 mole of chlorate/mole of free chlorine decomposed) and to a significant increase in the chlorine demand of pool water during the post-chlorination step. UV exposure followed by post-chlorination did not significantly affect the formation of haloacetic acids, led to a small increase in the concentrations of adsorbable organic halogen (AOX) and of chloral hydrate and markedly increased the formation of trihalomethanes (chloroform, bromodichloromethane, chlorodibromomethane), dichloroacetonitrile, 1,1,1-trichloropropanone and chloropicrin.

The kinetics of monochloramination of resorcinol, 4-chlororesorcinol, and 4,6-dichlororesorcinol have been investigated over the pH range of 5-12, at 23 +/- 2 degrees C. Monochloramine solutions were prepared with ammonia-to-chlorine ratios (N/Cl) ranging from 1.08 to 31 mol/mol. Under conditions that minimize free chlorine reactions (N/Cl > 2 mol/mol), the apparent second-order rate constants of monochloramination of resorcinol compounds show a maximum at pH values between 8.6 and 10.2. The intrinsic second-order rate constants for the reaction of monochloramine with the acid-base forms of the dihydroxybenzenes (Ar(OH)(2), Ar(OH)O(-), and Ar(O(-))(2)) were calculated from the apparent second-order rate constants. The stoichiometric coefficients for the formation of 4-chlororesorcinol by monochloramination of resorcinol and 4,6-dichlororesorcinol by monochloramination of 4-chlororesorcinol were found to be equal to 0.66 +/- 0.05 and 0.25 +/- 0.02 mol/mol, respectively at pH 8.6. A kinetic model that incorporates reactions of free chlorine and monochloramine with the different acid-base forms of resorcinol compounds simulated well the initial rates of degradation of resorcinol compounds and was useful to evaluate the contribution of free chlorine reactions to the overall rates of degradation of resorcinol at low N/Cl ratios.

The study of the occurrence and fate of pharmaceutical compounds in drinking or waste water processes has become very popular in recent years. Liquid chromatography with tandem mass spectrometry is a powerful analytical tool often used to determine pharmaceutical residues at trace level in water. However, many steps may disrupt the analytical procedure and bias the results. A list of 27 environmentally relevant molecules, including various therapeutic classes and (cardiovascular, veterinary and human antibiotics, neuroleptics, non-steroidal anti-inflammatory drugs, hormones and other miscellaneous pharmaceutical compounds), was selected. In this work, a method was developed using ultra performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) and solid-phase extraction to determine the concentration of the 27 targeted pharmaceutical compounds at the nanogram per litre level. The matrix effect was evaluated from water sampled at different treatment stages. Conventional methods with external calibration and internal standard correction were compared with the standard addition method (SAM). An accurate determination of pharmaceutical compounds in drinking water was obtained by the SAM associated with UPLC-MS/MS. The developed method was used to evaluate the occurrence and fate of pharmaceutical compounds in some drinking water treatment plants in the west of France.