Kinetics and thermodynamics of the formation of trihalomethanes

Résumé

The effect of contact time and temperature on the formation of trihalomethanes (THMs) was studied during the chlorination of Khandaq El-Sharqi canal, Egypt, under laboratory condition. Samples were collected from four positions of Khandaq El-Sharqi canal (Itay El-Baroud, Dinshal, Damanhour and El-Zawya). Increasing trihalomethanes formation has been observed with increasing contact time and temperature. In the presence of excess chlorine, trihalomethanes formation proceeds as a pseudo-first-order reaction. The rate constants of the formation of trihalomethanes at different temperatures (10, 20, 30 and 40 °C) were calculated. Values of rate constant given for chloroform (CFM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and total trihalomethanes (TTHMs) approached each other, whereas chloroform attained a higher value for each temperature. Thermodynamic parameters of activation (Δ H # , Δ S # and Δ G # ) for the formation of trihalomethanes were calculated by least square procedure program at 25 °C. The data showed that there is no significant change observed in Δ G # , and this is presumably due to the compensation between Δ H # and Δ S # to each other.

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