Continuous seawater disinfection by chlorine dioxide (ClO₂) was studied at residual concentrations of 0.2 and 0.4 mg ClO₂ L⁻¹ and compared with sodium hypochlorite (NaClO) disinfection at 1 mg L⁻¹ of ...free chlorine. The results revealed that both disinfectants decrease the biological activity and cell counts in seawater. When NaClO was used, both the cell counts and the adenosine triphosphate (ATP) level were diminished (1.8 log and 76 %, respectively); however, when ClO₂ was used, the ATP level decreased to the same level as with NaClO (78–84 %), but the cell counts were reduced only weakly (~0.1 log). The biofilm concentration in seawater without disinfectants reached 700 pg ATP cm⁻² after 40 days, whereas in the treated lines, the biofilms remained below 1 pg ATP cm⁻² irrespective of the disinfectant and dose used. ClO₂ generated much less trihalomethanes than NaClO (<1 vs. 154 μg L⁻¹). Bromoform (77–96 %) was the predominant chemical species found in disinfected seawater.
This study focused on (a) the development of a screening methodology, in order to determine the main experimental variables affecting chlorinated and brominated disinfection by-product (DBP) ...formation in water during chlorination experiments and (b) the application of a central composite design (CCD) using response surface methodology (RSM) for the mathematical description and optimization of DBP formation. Chlorine dose and total organic carbon (TOC) were proven to be the main factors affecting the formation of total chlorinated DBPs, while chlorine dose and bromide concentration were the main parameters affecting the total brominated THMs. Longer contact time promoted a rise in chlorinated DBPs’ concentration even in the presence of a minimal amount of organic matter. A maximum production of chlorinated DBPs was observed under a medium TOC value and it reduced at high TOC concentrations, possibly due to the competitive production of brominated THMs. The highest concentrations of chlorinated THMs were observed at chlorine dose 10 mg L
−1
and TOC 5.5 mg L
−1
. The formation of brominated DBPs is possible even with a minimum amount of NaOCl in the presence of high concentration of bromide ions. Brominated DBPs were observed in maximum concentrations using 8 mg L
−1
of chlorine in the presence of 300 μg L
−1
bromides.
Headspace-solid-phase microextraction (HS-SPME) combined with gas chromatography-electron capture detector (GC-ECD) has been developed and studied for the determination of trihalomethanes (THMs) in ...treated water samples. Experimental parameters such as the selection of thickness of the polymer coating, addition of salt, magnetic stirring, extraction temperature, and extraction time were studied. Extraction of the analytes was performed using HS-SPME with a 100µm poly(dimethylsiloxane) coating followed by thermal desorption at 250°C and GC analysis. The optimized conditions were 20min extraction time at 35°C with 25w/v% NaCl. Analytical parameters such as linearity and limit of detection were also evaluated. The linear range of 1–100µg/l was established with relative standard deviations (%RSD) within the range, 1.3–11.7%. The limits of detection (LODs) were ranged from 1.4ng/l to 6.1ng/l. The average THM concentration was 88.16µg/l which was well within the proposed European Union directive of 100µg/l.
A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in ...Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV
254), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.
In many drinking water treatment plants, the chlorination process is one of the main techniques used for the disinfection of water. This disinfecting treatment leads to the formation of ...trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform. In this study, headspace-solid-phase microextraction (HS-SPME, 85
μm carboxen/polydimethylsiloxane fiber) technique was applied for the analysis of THMs in drinking water. The effects of experimental parameters such as kinds of SPME fiber, the volume ratio of sample to headspace, the addition of salts, magnetic stirring, extraction temperature, extraction time and desorption time on the analysis were investigated. Analytical parameters such as linearity, repeatability and limit of detection were also evaluated. The results of THMs from the survey of Seongnam (Korea) drinking water samples showed that the highest total trihalomethane and chloroform were 24.03 and 13.34
μg/l, which were well within the Korean drinking water quality standard of 100 and 80
μg/l, respectively.
Volatile organic compounds (VOCs) including major trihalomethanes (THMs) in bottled and tap waters from Central Missouri were quantified and compared with drinking water guidelines. Tap (
n
=
34), ...spring (3 brands,
n
=
25), purified (8 brands,
n
=
58), distilled (3 brands,
n
=
12) and flavored waters (5 brands,
n
=
34) along with Missouri River water (
n
=
30), were analyzed by purge and trap gas chromatograph–mass spectrometry (GC–MS) using USEPA method 524.2. The mean recoveries of the internal and surrogates standards were fluorobenzene: 100%, benzene d5-, chloro: 100% and 1,4-dichlorobenzene d4: 96%. Approximately 97% of all drinking water types were found to be safe for human consumption. However, two tap water samples recorded bromodichloromethane concentrations above the 60
μg/L World Health Organization (WHO) limit. Moreover, six tap water samples exceeded both the 80
μg/L USEPA Stage I limit and the 100
μg/L European Community (EC) maximum contaminant concentration (MAC) for total THMs (TTHMs) in drinking water. TTHMs in the water types ranged from 0–322
μg/L (tap), 0.1–0.3
μg/L (spring), 0–7.6
μg/L (purified), 0.1–18.1
μg/L (distilled), and 0–5.7
μg/L (flavored). Kruskal–Wallis Chi square approximation showed significant differences (
P
<
0.001) in the levels of THMs found in the water types. Principal components (PC1 and PC2) with 97% total variance suggested similarities in most drinking waters except for Boonville and Columbia tap waters. Dendrogram plots of TTHMs and Σ VOCs revealed two principal clusters with Columbia and Boonville tap waters in a different cluster and also distant from other water types.
Because of increasing concern for both microbial control and disinfection by-products (DBPs) formation, water utilities are strictly examining and optimizing disinfection practices. In this study, ...modeling of trihalomethanes (THMs) formation at processed water of the Kagithane water treatment plant in Istanbul City was conducted. Data for THMs and other water quality and operational parameters were generated through a 12-month sampling program between January and December 2003. A multiple linear regression model was developed to predict THMs concentrations in processed water. Routinely measured parameters including total organic carbon (TOC), pH, temperature, and chlorine dose were used to develop the model for the prediction of THMs. Both pH (
r = 0.963) and temperature (
r = 0.921) were found to be the parameters of the highest statistical significance as predictors for THMs occurrence. The regression analysis resulted in a model that is directly applicable to the chlorination of raw waters. This indicated that the linear models developed could be used to estimate THMs concentration for different water quality and treatment processes with different operational conditions.
AbstractNatural organic material (NOM) has been the focus of many studies because of its ability to compromise water treatment processes. This case study utilized ultraviolet (UV) spectroscopy and ...molecular weight distributions to investigate the impact of six water treatment processes (alum coagulation, magnetic ion exchange (MIEX) resin treatment, chlorination, ozonation, powdered activated carbon (PAC) adsorption, and biological sand filtration) on the removal of NOM from an Australia water source, Myponga Reservoir. Each of these processes displayed different effects on the concentration and character of NOM. The removal of dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254) by MIEX and the biological sand filter was shown to follow first-order kinetics with rate constants ranging from 9.0×10−8 s−1 (biological sand filter) to 6.3×10−5 s−1 (MIEX treatment). UV spectroscopic investigations showed the potential to predict the formation of disinfection by-products from chlorination with strong correlations (R2 of 0.96) observed between the formation of trihalomethanes and the differential UV absorbance at 265 nm. Ozonation and biological sand filtration also appeared to target NOM absorbing at 265 nm. Molecular weight distribution analyses showed MIEX treatment to be the most effective single process in achieving high removals of a wide molecular weight range of NOM, consistent with the high removals of DOC and UV254 (up to 90% and 80% removal, respectively). The combination of alum and PAC, treatment options which exist at the majority of Australian water treatment plants, also proved effective for high NOM removal over a wide range of molecular weights, where alum effectively removed high molecular weight compounds, and PAC effectively removed low molecular weight compounds. This study has demonstrated that valuable information can be gained through simple manipulation of UV absorbance and molecular weight distribution data, which could be beneficial to water utilities in not only facilitating the selection of treatment processes when commissioning WTPs, but also optimizing existing treatment processes for effective NOM removal.
Trihalomethanes (THMs) are the most abundant disinfection byproducts (DBPs) of the chlorination disinfection. THMs speciation and their geospatial distribution were examined in 58 locations ...throughout the water distribution network of Karachi city. THMs (CHCl
3
, CHCl
2
Br, CHClBr
2
and CHBr
3
) and physico-chemical parameters (pH, TDS, DO, Residual chlorine, temperature and TOC) were determined. CHCl
3
was the major THM found in all water samples of 58 locations, which accounted for 91.69 % of the total THMS followed by CHCl
2
Br (5.69 %), CHClBr
2
(1.78 %) and CHBr
3
(0.85 %). Total THMs level exceed the maximum contamination level of WHO and USEPA at some locations. Varying nature of correlation from high to low was found within THMs and among the physico-chemical parameters. GIS linked geospatial analysis revealed the association of THMs level with demographical and geological based variations from east to west of Karachi city. Continuous monitoring program and legislation for the contaminant levels were suggested to avoid adverse public health impact of THMs in drinking water supplies.
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