Chloral hydrate control by point-of-use and household appliances

Unlike other pollutants occurring in raw water, disinfection by-product (DBP) is usually produced at the end point of the drinking water treatment plant (DWTP) and, once formed, it cannot be readily removed by engineering processes. As a result, treatments of existing DBP by point-of-use and/or household appliances have become the last line of defense in alleviating the impact of DBP for general family. In this study, we evaluated the effectiveness of several residential options, including reverse osmosis (RO) and granular activated carbon (GAC) cartridges, microwave oven, boiler, and ultrasonic cleaner, on the removal of chloral hydrate (CH) under various operating (e.g., power, stirring speed) and environmental (e.g., pH, initial concentration) conditions. The results indicate that heating by either boiler or microwave oven can reduce CH from tap water significantly (>90%) under automatic switch-off conditions. The degree of removal by heating was always greater in tap water than in ultrapure water, implying that certain compounds or residual chlorine in tap may have accelerated the CH transformation process, while CH removal in ultrapure water is mainly controlled by thermal hydrolysis. In contrast, volatilization by stirring or sonication exhibited little capacity (<5%) to remove CH. RO cartridge eliminated >90% of CH regardless of operating pressure, initial CH concentration, pH, and type of water, proving it as a robust tool in dealing with drinking water issues. Cartridges with GAC showed some potentials (45∼90%) for CH removal, which were much greater than cartridges made by PP cotton and carbon block filter (<5%); however, the adsorption ability of GAC can be highly compromised by rapid flowrate and limited retention time, which suggests that GAC adsorption is not the major contributor to CH removal in a commercial water purifier. Overall, the data have proven the effectiveness of many POU and household appliances on CH removal, and may help consumers to relieve DBP concerns in case of emergency.