Formation and Removal of Trihalomethanes and Trichloroethylene at Different Stages of Tap Water Aftertreatment for Beverage Production

Abstract

The formation and removal of trihalomethanes and trichloroethylene at an existing beverage production enterprise at the stages of the sodium hypochlorite disinfection of water from the centralized drinking waterwork system after treatment with ammonium chloride have been studied. To clarify the mechanism of formation of trihalomethanes and trichloroethylene, the concentrations of organic and organochlorine compounds have been analyzed after each of the three sodium hypochlorite introduction stages alongside with the dynamics of their change in the tap water supplied to the enterprise. It has been shown that the highest amount of organochlorine compounds is formed in the process of filtration on sand filters. The chloroform concentration is ranged within 40–65 μg/dm3, and the trichloroethylene concentration is 34–72 μg/dm3, being respectively 67 and 61% higher than in the tap water. One of the main reasons for the excessive formation of trihalomethanes and trichloroethylene is the disinfection of incoming tap water by means of free chlorine in the presence of a residual amount of chlorine bonded into organic and inorganic chloramines. The mechanism of the excessive formation of organochlorine compounds on sand filters is described as associated with disinfection by means of free chlorine in the absence of ammonium ions and also with a high content of organic compounds in the incoming water and a large dirt absorbing capacity of the filter load. Some variants are proposed for maintaining the optimal chlorination regime at the water aftertreatment stages to provide the formation of a minimum amount of organochlorine compounds, the epidemiological safety of water, the fulfilment of microbiological requirements to filter loads, and the content of residual bonded and free chlorine in the prepared water and its microbiological parameters. To prevent the formation of organochlorine compounds, water disinfection is recommended to perform with the use of hypochlorite with ammonization by ammonium sulfate or with the use of in situ synthesized monochloramine.