Nassar R, Mokh S, Rifai A, Chamas F, Hoteit M, Al Iskandarani M. Transformation of sulfaquinoxaline by chlorine and UV light in water: kinetics and by-product identification. Environ Sci Pollut Res Int. 2017 Dec 1. doi: 10.1007/s11356-017-0814-4.
Sulfaquinoxaline (SQX) is an antimicrobial of the sulfonamide class, frequently detected at low levels in drinking and surface water as organic micropollutant. The main goal of the present study is the evaluation of SQX reactivity during chlorination and UV irradiations which are two processes mainly used in water treatment plants. The SQX transformation by chlorination and UV lights (254 nm) was investigated in purified water at common conditions used for water disinfection (pH = 7.2, temperature = 25 °C, [chlorine] = 3 mg L-1). The result shows a slow degradation of SQX during photolysis compared with chlorination process. Kinetic studies that fitted a fluence-based first-order kinetic model were used to determine the kinetic constants of SQX degradation; they were equal to 0.7 × 10-4 and 0.7 × 10-2 s-1 corresponding to the half time lives of 162 and 1.64 min during photolysis and chlorination, respectively. In the second step, seven by-products were generated during a chlorination and photo-transformation of SQX and identified using liquid chromatography with electrospray ionization and tandem mass spectrometry (MS-MS). SO2 extrusion and direct decomposition were the common degradation pathway during photolysis and chlorination. Hydroxylation and isomerization were observed during photodegradation only while electrophilic substitution was observed during chlorination process.
Crider Y, Sultana S, Unicomb L, Davis J, Luby SP, Pickering AJ. Can you taste it? Taste detection and acceptability thresholds for chlorine residual in drinking water in Dhaka, Bangladesh. The Science of the total environment. 2017 Sep 20;613-614:840-846. doi: 10.1016/j.scitotenv.2017.09.135.
Chlorination is a low-cost, effective method for drinking water treatment, but aversion to the taste or smell of chlorinated water can limit use of chlorine treatment products. Forced choice triangle tests were used to evaluate chlorine detection and acceptability thresholds for two common types of chlorine among adults in Dhaka, Bangladesh, where previous studies have found low sustained uptake of chlorine water treatment products. The median detection threshold was 0.70 mg/L (n=25, SD=0.57) for water dosed with liquid sodium hypochlorite (NaOCl) and 0.73mg/L (n=25, SD=0.83) for water dosed with solid sodium dichloroisocyanurate (NaDCC). Median acceptability thresholds (based on user report) were 1.16 mg/L (SD=0.70) for NaOCl and 1.26mg/L (SD=0.67) for NaDCC. There was no significant difference in detection or acceptability thresholds for dosing with NaOCl versus NaDCC. Although users are willing to accept treated water in which they can detect the taste of chlorine, their acceptability limit is well below the 2.0mg/L that chlorine water treatment products are often designed to dose. For some settings, reducing dose may increase adoption of chlorinated water while still providing effective disinfection.
Zhang K, Zhou X, Zhang, Mao M, Li L, Liao W. Kinetics and mechanisms of formation of earthy and musty odor compounds: Chloroanisoles during water chlorination. Chemosphere. 2016 Aug 22;163:366-372. doi: 10.1016/j.chemosphere.2016.08.051.
Chloroanisoles are often reported as off-flavor compounds which produce an earthy and musty flavors and odors in drinking water. To improve understanding and ultimately minimize the formation of 2,4-dichloroanisole (2,4-DCA), 2,6-dichloroanisole (2,6-DCA) and 2,4,6-trichloroanisole (2,4,6-TCA), which have low odor threshold concentrations (OTC: 0.03-4 ng L-1), a kinetic database for the chlorination of anisole was established by kinetic measurements. The results showed that HOCl reacted with anisole in acidic solution, with the hydrogen ion as an important catalyst. Quantification of product distribution of the produced chloroanisoles demonstrated that a chlorine attack in the para-position was favored over the ortho-position. A kinetic model was formulated, which permitted investigation of the relative importance of the chlorine dose and other water quality parameters including the concentrations of anisole and several metal ions, as well as temperature, on the product distribution of chloroanisoles. In general, high chlorine doses led to low concentrations of intermediates. The presence of ions such as Fe3+ and Al3+ facilitated the formation of chloroanisoles, but Zn2+ and Mn2+ did not. The kinetic model can be applied to optimize water chlorination and minimize earthy and musty odors.
Mathieu L, Francius G, El Zein R, Angel E, Block JC. Bacterial repopulation of drinking water pipe walls after chlorination. Biofouling. Biofouling. 2016 Sep;32(8):925-34. doi: 10.1080/08927014.2016.1212989/
The short-term kinetics of bacterial repopulation were evaluated after chlorination of high-density polyethylene (HDPE) colonized with drinking water biofilms and compared with bare HDPE surfaces. The effect of chlorination was partial as a residual biofilm persisted and was time-limited as repopulation occurred immediately after water resupply. The total number of bacteria reached the same levels on both the bare and chlorinated biofilm-fouled HDPE after a seven-day exposure to drinking water. Due to the presence of a residual biofilm, the hydrophobicity of chlorinated biofilm-fouled surface exhibited much lower adhesion forces (2.1 nN) compared to bare surfaces (8.9 nN). This could explain the rapid repopulation after chlorination, with a twofold faster bacterial accumulation rate on the bare HDPE surface. γ-Proteobacteria dominated the early stages of repopulation of both surfaces and a shift in the dominance occurred over the colonization time. Such observations define a timescale for cleaning frequency in industrial environments and guidelines for a rinsing procedure using drinking water.
How ZT, Linge KL, Busetti F, Joll CA. Organic chloramines in drinking water: An assessment of formation, stability, reactivity and risk. Water Research 2016 Feb 11;93:65-73. doi: 10.1016/j.watres.2016.02.006.
Although organic chloramines are known to form during the disinfection of drinking water with chlorine, little information is currently available on their occurrence or toxicity. In a recent in vitro study, some organic chloramines (e.g. N-chloroglycine) were found to be cytotoxic and genotoxic even at micromolar concentrations. In this paper, the formation and stability of 21 different organic chloramines, from chlorination of simple amines and amino acids, were studied, and the competition between 20 amino acids during chlorination was also investigated. For comparison, chlorination of two amides was also conducted. The formation and degradation of selected organic chloramines were measured using either direct UV spectroscopic or colorimetric detection. Although cysteine, methionine and tryptophan were the most reactive amino acids towards chlorination, they did not form organic chloramines at the chlorine to precursor molar ratios that were tested. Only 6 out of the 21 organic chloramines formed had a half-life of more than 3 h, although this group included all organic chloramines formed from amines. A health risk assessment relating stability and reactivity data from this study to toxicity and precursor abundance data from the literature indicated that only N-chloroglycine is likely to be of concern due to its stability, toxicity and abundance in water. However, given the stability of organic chloramines formed from amines, more information about the toxicity and precursor abundance for these chloramines is desirable.
Zheng M, He C, He Q. Fate of free chlorine in drinking water during distribution in premise plumbing. Ecotoxicology. 2015 Sep 25.
Free chlorine is a potent oxidizing agent and has been used extensively as a disinfectant in processes including water treatment. The presence of free chlorine residual is essential for the prevention of microbial regrowth in water distribution systems. However, excessive levels of free chlorine can cause adverse health effects. It is a major challenge to maintain appropriate levels of free chlorine residual in premise plumbing. As the first effort to assessing the fate of chlorine in premise plumbing using actual premise plumbing pipe sections, three piping materials frequently used in premise plumbing, i.e. copper, galvanized iron, and polyvinyl chloride (PVC), were investigated for their performance in maintaining free chlorine residual. Free chlorine decay was shown to follow first-order kinetics for all three pipe materials tested. The most rapid chlorine decay was observed in copper pipes, suggesting the need for higher chlorine dosage to maintain appropriate levels of free chlorine residual if copper piping is used. PVC pipes exhibited the least reactivity with free chlorine, indicative of the advantage of PVC as a premise plumbing material for maintaining free chlorine residual. The reactivity of copper piping with free chlorine was significantly hindered by the accumulation of pipe deposits. In contrast, the impact on chlorine decay by pipe deposits was not significant in galvanized iron and PVC pipes. Findings in this study are of great importance for the development of effective strategies for the control of free chlorine residual and prevention of microbiological contamination in premise plumbing.
Zhang TY, Lin YL, Xu B, Xia SJ, Tian FX, Gao NY. Effect of UV irradiation on the proportion of organic chloramines in total chlorine in subsequent chlorination. Chemosphere. 2015 Sep 29;144:940-947. doi: 10.1016/j.chemosphere.2015.09.074.
This study investigated the changes of chlorine species and proportion of organic chloramines during the chlorination process after UV irradiation pretreatment in drinking water. It was found that the UV pretreatment could enhance the percentage of organic chloramines by increasing free chlorine consumption in the chlorination of raw waters. The percentage of organic chloramines in total chlorine increased with UV intensity and irradiation time in raw waters. However, for the humic acid synthesized water, the percentage of organic chloramines increased first and then decreased with the increase of UV irradiation time. The value of SUVA declined in both raw and humic acid synthesized waters over the UV irradiation time, which indicated that the decomposition of aromatic organic matter by UV could be a contributor to the increase of free chlorine consumption and organic chloramine proportion. The percentage of organic chloramines during chlorination of raw waters after 30-min UV irradiation pretreatment varied from 20.2% to 41.8%. Total chlorine decreased obviously with the increase of nitrate concentration, but the percentage of organic chloramines increased and was linearly correlated to nitrate concentration.