Sustainable and effective control of trihalomethanes in the breakpoint chlorination of wastewater effluents

Abstract

The control of trihalomethanes (THMs) in waters subjected to chlorination is essential for protecting public health. However, the necessary means are not always available, especially in developing countries and regions. Under circumstances of scarce resources, one can utilize various means available for the control of THMs: a simple and affordable analytical method for testing of THMs, the study of the parameters tested routinely that could be used as indicators and the dose of chlorine used for the chlorination process. The objective of this work was to study the potential formation of THMs in wastewater effluents using a simple method of detection and various doses of chlorine in relation to the breakpoint and to validate some commonly determined parameters as indicators of THM formation. THM concentrations were measured using a simple spectrophotometric method based on the Fujiwara reaction. To determine the chlorine demand, a super-chlorination was performed and free and residual chlorine was measured; the mean value of chlorine demand was 166.6 mg Cl₂/L. The chlorination with concentrations well below the chlorine demand produces a significant reduction in microbial content. With regard to the formation of THMs the higher the dose of chlorine added, the higher the concentration of THMs. In relation to commonly determined parameters our data only provide a logarithmic linear regression between THMs and ammonium. According to our results, the breakpoint must be determined for the chlorination of sewage and their effluents, and chlorination should be performed with concentrations of chlorine at approximately 1/3 of the demand.

Keywords:

• chlorination
• chlorine demand
• Fujiwara reaction
• trihalomethanes
• wastewater

Acknowledgements

This study was financed by the Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública (CIBERESP), Instituto de Salud Carlos III, Madrid. Spain. We would like to acknowledge Cesar Criado Sánchez, laboratory technician of the Department of Preventive Medicine and Public Health, Faculty of Pharmacy, University of Granada, Spain, for his invaluable help in making this study possible.