Kinetics and thermodynamics of the formation of trihalomethanes

Abstract

Abstract 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 (ΔH #, ΔS # and ΔG #) 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 ΔG #, and this is presumably due to the compensation between ΔH # and ΔS # to each other.

Keywords

• Trihalomethanes
• Thermodynamic parameters of activation
• Rate constant
• Khandaq El-Sharqi canal
• Egypt