Effect of copper on trihalomethane formation during chlorination of water and wastewater

Ravikrishna Duggirala, Purdue University

Abstract

Copper (II) increases the formation of trihalomethanes (THMs) during chlorination of humic acid and some model compounds. The ability of copper to catalyze THM formation appears to be linked to the formation of copper complexes by THM precursors. Humic substances form stable and labile complexes with transition metals. The complexation of copper with humic materials was characterized by potentiometric titrations using a cupric ion selective electrode. The results demonstrated that most of the copper was complexed by humic material at copper concentrations likely to be seen in chlorine based disinfection processes. Experiments were designed using fractional factorials to study the effect of copper on chloroform formation from humic acid and to evaluate various first-order and second-order interactions. The results were used to build second-order response surface models at different times, and non-linear models that incorporate the effect of time. The results demonstrate that there is a substantial increase in THM formation in the presence of copper (II). The results also indicate that copper (II) enhances THM formation by activating a portion of humic acid which is otherwise not a significant contributor to THM formation. The non-linear models indicated that THM formation is a stronger function of chlorine dose in the presence of copper. Experiments carried out with several model compounds showed that copper enhances the formation of trihalomethanes by activating citric acid and similar structures in humic acid. Based on a literature review, a mechanism for the formation of trihalomethanes from citric acid is proposed. Copper (II) is expected to enhance the THM formation by catalyzing the decarboxylation reactions. The effect of bromide ion in conjunction with the effect of copper was also studied. Copper (II) enhanced formation of brominated THMs in a manner similar to the enhancement of chloroform formation. The results from these studies demonstrated that copper is a significant factor in THM formation during chlorination of water and wastewater. Control of copper (II) will be important in THM control during chlorination of water and wastewater.

Degree

Ph.D.

Advisors

Blatchley, Purdue University.

Subject Area

Chemical engineering|Environmental science

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