Chapter 19
Chloral Hydrate Control by Point-of-Use and Household Appliances Downloaded by RMIT UNIV on June 26, 2016 | http://pubs.acs.org Publication Date (Web): August 24, 2015 | doi: 10.1021/bk-2015-1190.ch019
Baiyang Chen,* Xiaoqi Guo, Zhong Tang, and Wenbiao Jin Harbin Institute of Technology Shenzhen Graduate School, Shenzhen Key Laboratory of Water Resource Utilization and Environmental Pollution Control, Shenzhen, China, 518055 *E-mail:
[email protected]. Phone: 86-134-80727605.
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 (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 © 2015 American Chemical Society Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
than cartridges made by PP cotton and carbon block filter (99% in purity) instead of dissolved in solvent to avoid potential interference of the solvent (21). Besides CH, the methyl-tert-butyl ether (MTBE) used for CH extraction and phosphorous buffer used for pH control were purchased from Aladdin Inc. at analytical grade (>99.9% in purity). Prior to experiments, stock CH solution was prepared by ultrapure water at a concentration of 2g/L and stored in a freezer at 4°C temperature if not used immediately. In all tests, control experiments were conducted. The water samples were obtained from the city of Shenzhen, China, including lake water taken from Xili Lake, a drinking water source of the city; tap water from the laboratory; and ultrapure water produced on site by a Millipore water generator (Direct-Q3) with UV sterilizer. The lake and tap samples were filtered through a 0.45 µm glass fiber filter (Xingya, Co., Ltd) before use, and some water qualities are listed in Table 1. The selection of raw water for tests was intended to examine the potential influences of NOM and ions on CH treatability, although in practice it is impossible to have CH in raw water. Similarly, a comparison of ultrapure water and tap water may help better understand the CH treatment differences between ideal and real conditions. Analytical Methods CH was detected by a GC equipped with a ECD detector (GC-9720, Fuli, China) according to a modified EPA method 551.1, with the method detection limit (MDL) of 0.35 µg/L. Briefly, CH extraction was carried out for a 25ml sample by applying 5g of NaCl and 3ml of MTBE, shaking for 1 minute on a lab-dancer (IKA, Gemany), and then letting it stand for 20 minutes. The GC column was initially set to be 60 °C for 3 minutes and then ramped up to 150°C 365 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
Downloaded by RMIT UNIV on June 26, 2016 | http://pubs.acs.org Publication Date (Web): August 24, 2015 | doi: 10.1021/bk-2015-1190.ch019
with a 20°C/min rate, and maintained the temperature for 1 minute; the flowrate of carrier gas (99.999% nitrogen in purity) was 2ml/min, and the temperature of ECD detector was set at 280°C. Residual chlorine was analyzed by the DPD method using a spectrophotometer (Hach 3900, USA) according to EPA 330.5. Chloride was analyzed by an ion chromatography instrument (IC2010, Tosoh Inc., Japan) with a MDL of 1 µg/L. Conductivity was recorded using an electrode (SX-650, San-Xin Instrumentation, Inc., China), and pH was analyzed using an electrode meter (pH100, Extech Instruments Corporation, USA). Dissolved organic carbon (DOC) was assessed by a TOC analyzer (TOC-LCPH, Shimadzu, Japan) according to the EPA 415.3 method.
Table 1. Characteristics of Waters in This Study COND (μs)
TDS (mg/L)
TOC (mg/L)
Ultrapure Water
0.056
97% of CH removals. These studies, however, did not consider the automatic switch-off function of boilers commonly used by the public. Since a boiler stops heating immediately, which often takes seconds, a more practical evaluation of the heating process (i.e., 90%), but not as high for CH in ultrapure waters (~20%). The underlying mechanism is perhaps attributable to the presence of residual chlorine, but not the salinity of the water. The reduction of CH in ultrapure water may be due to the thermal hydrolysis effect. CH is a non-volatile compound and, as a result, stirring or ultrasonication technology are unable to lower its concentration to any great extent (
