Abstract

This study presents an overview of the changes in humic acids, which are disinfection by-product precursors in a raw water canal, Bangkok, Thailand, during different seasons. Fluorescence excitation–emission matrix (EEM) spectroscopy was employed to characterize and quantify spatial and seasonal variations of dissolved organic matter (DOM) along a raw water canal of the Metropolitan Waterworks Authority (MWA) Bangkok, Thailand. A total of 276 raw water samples were collected from 23 stations during the winter, summer and rainy season. Results indicate that hydrophobic fractions made up the majority of DOM and this water source also had high specific UV absorbance (SUVA). Seasonal variation of DOM was found to be more pronounced than geographical variation along the canal. The presence of humic substances was the highest in the rainy season due to rainfall and surface runoff, while soluble microbial by-product-like substances were found only in summer. The results provide an insight into the prediction of humic acids in source water, which benefits the MWA in being aware of seasonal variation in water quality.

INTRODUCTION

Water quality is always an issue for developing countries. Problems include inadequate supply and access to water, poor sanitation, and contamination in natural water. To inactivate pathogens and to ensure sanitation conditions are met, drinking water treatment plants across Thailand use disinfectants (chlorine, chloramine, or chlorine dioxide) in their disinfection systems. Bangkhen Water Treatment Plant (WTP), managed by the Metropolitan Waterworks Authority (MWA) of Thailand, is the largest water supply plant in Thailand with a capacity of 3.6 million m3/day covering 3,195 km2 in three provinces: Bangkok, Nonthaburi, and Samutprakarn.

Bangkhen WTP used a conventional treatment process (coagulation, flocculation, sedimentation, and sand filtration) to remove dissolved organic matter (DOM) followed by chlorination to inactivate pathogenic microorganisms. Unfortunately, the conventional treatment process is unable to remove all of the DOM presented in raw natural water. When residual DOM is chlorinated, it acts as a precursor to disinfection by-products (DBPs), which are considered carcinogenic substances and are regulated in drinking water standards by the USEPA (US Environmental Protection Agency 2001). Trihalomethanes (THMs) and haloacetic acids (HAAs) are two dominant species of halogenated DBPs formed in the chlorination process. THMs, which are generally reported in terms of the sum of chloroform, bromodichloromethane, dibromochloromethane, and bromoform, were the largest class of DBPs detected (Krasner et al. 2006).

Understanding of the characteristics and sources of DOM and how they may enter and change during the water canal and unit processes in water supply plants is critical to assure good water quality and minimize DBP formation during chlorination. Panyapinyopol et al. (2005) have evaluated THM precursors at Bangkhen WTP and reported that chlorination at the plant led to formation of mostly chloroform. However, little is known about the characteristics of DOM along the water canal that transports raw water from Chao Phraya River, the main river in Thailand, to Bangkhen WTP. Considering the canal is located in the heart of Bangkok, spatiotemporal characteristics of DOM should vary substantially depending on the natural and human activities along the canal. As of today, the characteristics of DBP precursors in the raw water canal intake to Bangkhen WTP that might effect THMs formation in different seasons have not been comprehensively studied.

Because DOM is a heterogeneous mixture and its composition varies, a number of researchers have focused on DOM characterization related to the formation of DBPs (Plewa et al. 2008; Matilainen et al. 2011). Humic substances, including humic and fulvic acids, are a hydrophobic fraction of DOM that were reported as important DBP precursors (Leenheer & Croué 2003; Krasner et al. 2009). Humic acids may not react directly with chlorine in forming THMs, but their degradation products do. A basic DOM measurement method, e.g. dissolved organic carbon (DOC), is a gross measurement that cannot provide details of DOM source and composition and also lacks information regarding the humic fraction of DOM. Thus, a better DOM characterization and understanding of changes in DOM composition in raw natural water could lead to a better strategy to control chlorination conditions in a WTP.

A technique that has been increasingly used for DOM characterization is fluorescence excitation–emission matrix (EEM) spectroscopy (Coble 1996). EEM analysis provides rapid and non-invasive analysis of DOM properties with small sample volume requirement (Bridgeman et al. 2011), and it provides information regarding type, structure, and abundance of functional groups of DOM (Stedmon et al. 2011). EEM has been applied to track DOM in a WTP (Baghoth et al. 2011) and also changes in fluorescence DOM were related to DBP formation potential (Lyon et al. 2014). Based on EEM data, Chen et al. (2003) successfully classified DOM into five excitation–emission regions including aromatic protein I, aromatic protein II, fulvic acid-like, humic acid-like, and soluble microbial by-product-like.

Accordingly, this study aims to qualitatively and quantitatively investigate humic acid concentration along the raw water canal that is the intake to Bangkhen WTP through the year. The seasonal changes in spatiotemporal characteristics of humic acid were evaluated using information from DOC, UV absorbance at 254 nm (UV254), specific UV absorbance (SUVA), and fluorescence EEM spectroscopy. The results provide an insight into the prediction of humic acid, which is THM precursors, which benefits the WTP in being aware of water quality and disinfection parameters that affect the occurrence, formation, and control of THMs.

MATERIALS AND METHODS

The water samples were collected from Sam Lae raw water pump station, near Chao Phraya River, and along the 18-kilometre raw water canal before being sent to Bangkhen WTP in Bangkok, Thailand. The total sampling locations were 23 points (Figure 1).

Figure 1

Sampling locations along the raw water canal, from Sam Lae pump station to WTP intake.

Figure 1

Sampling locations along the raw water canal, from Sam Lae pump station to WTP intake.

Sampling locations are located in community areas which are likely to be contaminated by human activities and are 800 metres apart on average. As reported by MWA staff, the depth of the raw water canal was in the range of 3–6 metres. Water was sampled from a depth of 1.0 metres from the water surface, then the samples were immediately stored in 2 L bottles in an ice box. All sample points, starting from Sam Lae station to Bangkhen WTP, were collected on one day of every month during the period of August 2015 to July 2016, resulting in a total number of 276 samples. Samples were categorized into three groups according to season in Thailand, which is the rainy season (Aug–Oct 2015), winter (Nov 2015–Feb 2016), and summer (Mar–June 2016). For the rainy season sample collection, samples were collected 1–2 days after the prior rain.

Once arrived in the laboratory, samples were filtered through 0.45 μm cellulose acetate membrane filter within 24 hours after collection. Analytical methods for water quality parameters analyzed in this study are listed in Table 1. Also, the procedures of sample collection and analysis in this study are summarized in Figure 2.

Table 1

Analytical methods

ParametersInstrumentsMethods
Dissolved organic carbon (DOC) TOC Analyzer TOC-VCSH, Shimadzu Standard method 5310 B 
Humic acid (HA) Spectrofluorometer, JASCO FP-8200 Direct measurement 
UV254 UV-Visible Spectrophotometer, Thermo Scientific Evolution 60 S Standard method 5910 B 
Specific ultraviolet absorbance (SUVA) − Standard method 5910 B 
ParametersInstrumentsMethods
Dissolved organic carbon (DOC) TOC Analyzer TOC-VCSH, Shimadzu Standard method 5310 B 
Humic acid (HA) Spectrofluorometer, JASCO FP-8200 Direct measurement 
UV254 UV-Visible Spectrophotometer, Thermo Scientific Evolution 60 S Standard method 5910 B 
Specific ultraviolet absorbance (SUVA) − Standard method 5910 B 

Note: DOC unit mgC/L, HA unit mgC/L, UV254 unit cm−1, and SUVA unit L m−1mg−1.

Figure 2

Procedures of sample collection and analysis.

Figure 2

Procedures of sample collection and analysis.

To evaluate seasonal changes of humic substances on the natural occurrence of THMs, water quality parameters analyzed included ultraviolet absorbance at 254 nm (UV254), DOC, SUVA, humic acid (HA), and bromide concentration. SUVA, defined as ultraviolet absorbance at 254 nm (UV254) normalized to DOC concentration (Weishaar et al. 2003), was used to indicate hydrophobicity of DOM. Direct quantitative measurement of humic acid (HA) was performed based on fluorescence properties of HA with EEM measurement. A standard humic acid solution was prepared using humic acid (Sigma-Aldrich) and a standard curve was generated by the quantitative calibration menu of a Jasco FP-8200 Spectrofluorometer. EEMs were collected using the Jasco FP-8200 Spectrofluorometer at excitation wavelengths from 220 to 600 nm at 5 nm intervals and emission wavelengths from 230 to 650 nm at 0.5 nm intervals. Sample EEMs were then blank-subtracted and the humic acid-like fraction of DOM was quantified based on a regional integration chart (Chen et al. 2003). Fluorescence intensities were calibrated and corrected using quinine sulfate and were expressed in terms of quinine sulfate units (QSU), in which 1 QSU is equivalent to the intensity of 1 ppb quinine sulfate in 0.05 M H2SO4 at emission/excitation wavelengths of 450/345 nm (Musikavong et al. 2007).

RESULTS AND DISCUSSION

Variations of DOC and HA concentrations

During August 2015 to July 2016 at 23 sampling points along the raw water canal, DOC and humic acid were in the range of 0.27–6.72 mgC/L and 0.16–4.49 mgC/L, respectively. We note that in August, September, December (2015) and January (2016), DOC measured in the beginning (A1–A4) and the middle zones (A9–A17) varied considerably (Figure 3(a)), while humic acid was more stable (Figure 3(b)). The fluctuation of DOC in the beginning zone could be explained by a turbulent flow at the raw water intake from Chao Phraya River, which diffused and dissolved sediments at the bottom of the canal. There are two underground pipes under the road in the middle zone of the canal, which also caused the turbulent flow and thus explained the variation of DOC in the middle zone.

Figure 3

Changes of (a) DOC and (b) humic acid during August 2015–June 2016.

Figure 3

Changes of (a) DOC and (b) humic acid during August 2015–June 2016.

The annual average of the pH in the canal was 7.64 ± 0.03, and this could promote dissolution of DOC from the sediments since humic acids and lignins dissolve more effectively in solutions with a high pH (Libecki & Dziejowski 2008). High DOC concentration does not only affect the quality of treated water, but also increases coagulant demand in the WTP, which increases the possibility of THM occurrence (Matilainen et al. 2010).

On each sampling day, change in HA concentration was relatively small through the 12-hour hydraulic retention time in the canal (Figure 3(b)). Even though there was a seasonal variation such that HA concentrations during September–November 2015 were higher than at other times, there was no significant difference in HA concentration within a day of sampling. The lack of daily variation of HA suggested that the measuring of HA concentrations as in mgC/L is not able to track changes of composition or quantity that might be caused by human contamination and natural degradation.

When DOC data was categorized according to season, it can be seen that DOC was more stable in summer compared with winter and rainy seasons (Figure 4). The average DOC concentrations were 1.79, 1.63, and 1.93 mgC/L in the rainy season, winter, and summer, respectively, and the annual average was 1.78 mgC/L. These results agree well with a previous study (Wei et al. 2008) reporting that the DOC concentration of East River in China varied as 1.1–2.0 mgC/L in the winter and rainy seasons, but the variation was relatively small in summer. Rakruam & Wattanachira (2014) also found that the DOC concentration of Ping River, Northern Thailand, was higher in the rainy season compared with the dry season and this behavior was explained by the greater turbidity of water in the rainy season.

Figure 4

DOC along the canal in rainy, winter, and summer season (August 2015–June 2016).

Figure 4

DOC along the canal in rainy, winter, and summer season (August 2015–June 2016).

Within the same season, DOC variation was not significant (p > 0.05) in summer and in the rainy season. The only significant difference within a season was that the DOC of November fluctuated more than that of other months in winter. This fluctuation could be explained by the tropical weather of Thailand still having plenty of rainfall in November.

Compared with DOC, humic acid concentrations along the canal were more stable within a sampling day (Figure 5). Evidently, the significant difference of humic acid concentrations (p < 0.05) in the 3 months of the rainy season was caused by the heavy rain that caused turbulent flow and thus canal bank erosion. The erosion could increase suspended solids in the receiving water body, causing high organic matter loading and consequently an increase in humic substances. A similar incident was previously reported in Maji Ya Chai River in Tanzania (Aschermann et al. 2016). For winter, November was the only month that had a fluctuation in humic acid and we also attributed this issue to rainfall in November. The difference of humic acid concentration in the summer months was not significant (p > 0.05), and this result agrees well with the fact that there was less rainfall and lower turbulent flow in summer.

Figure 5

Humic acids along the canal in rainy, winter, and summer season (August 2015–June 2016).

Figure 5

Humic acids along the canal in rainy, winter, and summer season (August 2015–June 2016).

The average annual HA value was 1.67 mgC/L with seasonal averages of 1.69, 2.20, and 1.24 mgC/L in the rainy season, winter, and summer, respectively. To evaluate DOM composition based on HA, the ratio of average HA concentration to average DOC concentrations was 1.67:1.78, suggesting that humic fractions accounted for more than 50% of the DOM pool. This finding is consistent with Leenheer & Croué (2003), however, this value is greater than a previous finding by Panyapinyopol et al. (2005) who characterized raw water of Bangkhen WTP and reported that hydrophobic acid (HPOA) made up 34% of DOC. The difference could be due to different methods of measurement, which were resin fractionation in the previous study and EEM spectroscopy in this study.

Variations of SUVA

The SUVA value was used to indicate the hydrophobicity of DOM and is a useful indicator of the DBP formation potential of the water (Singer et al. 2007). Raw water with high SUVA has a high ability to form THMs during chlorination. The average SUVA values were 9.01, 6.87, and 3.05 L mg−1m−1 for the rainy season, winter and summer, respectively (Figure 6).

Figure 6

SUVA along the canal in rainy, winter, and summer season (August 2015–June 2016).

Figure 6

SUVA along the canal in rainy, winter, and summer season (August 2015–June 2016).

SUVA fluctuated drastically in the rainy season and winter, and we attributed this issue to the turbulent flow from rainfall and surface drainage into the canal. Compared with another study (Kueseng et al. 2011), which reported that natural water in Northern Thailand had SUVA in the range of 1.7–3.1 L mg−1m−1, the SUVA in this study was higher. This issue could be attributed to the location of the canal in the capital city and surface drainage from roadsides having an effect on water quality in the canal. The high SUVA value >4 can be interpreted as showing that DOM in the water source is primarily hydrophobic, aromatic compounds (Matilainen et al. 2011; Rakruam & Wattanachira 2014), which is consistent with the HA and DOC results in the previous section. A previous study also indicated that water with high SUVA has greater DBP formation potential (Singer et al. 2007).

Modern measurement of DOM by fluorescence EEM

Fluorescence EEM was employed to indicate compositions and quantity of each fraction of DOM. Contour plots of EEM of water samples collected at Sam Lae station (A1) and the WTP intake (A23) in three seasons are shown in Figure 7.

Figure 7

Fluorescence EEM contours of humic acid at Sam Lae station and the intake to the MWA WTP during rainy, winter and summer season.

Figure 7

Fluorescence EEM contours of humic acid at Sam Lae station and the intake to the MWA WTP during rainy, winter and summer season.

As illustrated in Figure 7, EEM plots can be delineated into five excitation–emission regions, and each region represents the specific component of DOM. Regions I and II (Ex <250 nm/ Em <350 nm) indicate DOM associated with aromatic proteins such as tyrosine and tryptophan. Region III (Ex 200–250 nm/ Em >380 nm) represents fulvic acid-like substances. EEMs in Region IV (Ex 250–280 nm/ Em <380 nm) can be related to soluble microbial by-product-like substances. Fluorescence in Region V (Ex >280 nm/ Em >380 nm) has a similar peak position to that reported for the humic-like substances (Chen et al. 2003). Additionally, the relative fluorescence intensity (RFI) of water samples at specific wavelengths were determined to provide a quantitative insight explicitly in terms of the QSU.

The dominant peaks of EEMs in Figure 7(a)7(f) were those of humic acid-like substances (Region V), with RFI of 54.7–71.8 QSU in summer, 76.7–79.8 QSU in winter, and 129–134 QSU in the rainy season. The low fluorescence intensity in summer and winter compared with the rainy season agrees well with the DOC results. Additionally, EEMs in winter and the rainy season are visually similar, and only EEMs in summer were drastically different with a greater presence of peaks in Region IV. The appearance of peaks in Region IV indicates contamination by soluble microbial by-product-like substances. Given that microbial contributions to the DOM pool increase with increasing water residence time (Jutaporn et al. 2016), Region IV peaks were presumably from bacterial activities along the canal since water flowrate is low and residence time increases in summer.

EEMs of samples at Sam Lae station (A1)

The white arrows in Figure 7 represent positions of the dominant peaks of EEM spectra in each figure. Sam Lae station (sampling point A1) is the beginning of the water canal located close to Chao Phraya River. At Sam Lae station (Figure 7(a)7(c)), the positions of the dominant peaks were at the excitation–emission pairs (nm/nm) of 280/419 in the rainy season (Figure 7(a)), 280/413 in winter (Figure 7(b)), and 280/412 in summer (Figure 7(c)). Peak positions of humic-like DOM were previously reported at the excitation–emission pairs of 350/420–480 (Coble 1996), which is comparable to the peak positions in this study.

On average, the RFI of samples at Sam Lae station were 102, 99.3, and 58.0 QSU in the rainy season, winter, and summer respectively. While the RFI of the humic-like DOM remained low and rarely changed in summer, it increased significantly to as high as 120–129 QSU during September–November 2015 due to algal bloom and surface runoff into the canal. Algal bloom is associated with phytoplankton biomass, and thus increased chlorophyll a, which affects fluorescence spectra (Su et al. 2015). The surface runoff was due to flooding in Bangkok during the time period due to heavy rainfall, which could bring a considerable amount of organic contaminants into the water source.

EEM of samples at the intake to the water treatment plant (A23)

The end of the canal is at the intake to Bangkhen WTP (sampling point A23). EEMs of samples collected at the intake (Figure 7(d)7(f)) also showed the dominant peak positions in Region V. The positions of the dominant peaks of the rainy season, winter, and summer were at the excitation–emission pairs (nm/nm) of 280/418 (Figure 7(d)), 280/418 (Figure 7(e)), and 280/416 (Figure 7(f)), respectively. These results showed that positions of the dominant peaks were relatively constant through the year.

Seasonal average RFI in the rainy season, winter, and summer was 111, 96.5, and 51.2 QSU, respectively. By visual comparison of EEMs at Sam Lae station (A1) with those at the intake to WTP (A23) of the same season, for example when Figure 7(d) is compared with Figure 7(a), the differences are marginal. For a quantitative comparison, the average RFI at A1 and A23 in the rainy season was 102 and 111 QSU, respectively. This 8% difference confirmed that the geographical difference of the humic fraction of DOM was minor.

On the other hand, seasonal variation of humic substance at the intake can be seen in Figure 7(d) and 7(e), with the greater RFI in the rainy season and winter and lower RFI in summer. Similarly to Sam Lae station, DOM at the intake to the WTP also had higher RFI in the rainy season and lower RFI with presence of soluble microbial by-product-like substances in summer. Thus, the overall results can be concluded that the spatial effect from natural biodegradation and photo oxidation along the canal had less effect on the dynamics of the humic substances compared with seasonal variation. The fact that predominant peak positions of samples from every location were in Region V also suggested that humic substances are the main fractions of this water source.

ΔEEM of DOM at the beginning and at the end of the canal

We use a new approach, differential EEM (ΔEEM), in order to quantify and access the changes of DOM composition along the canal, as defined by Lavonen et al. (2015):

ΔEEM = change in fluorescence intensity of DOM

= EEMbeginning–EEMend

where EEMbeginning and EEMend are the excitation–emission intensity at the beginning (A1) and the end (A23) of the canal respectively. The calculation scheme of ΔEEM is shown in Figure 8(a)8(i). Figure 8(c) illustrates ΔEEM in the rainy season, which refers to the change in DOM from Sam Lae station (A1, Peak A) to the end of the intake to the WTP (A23, Peak B). ΔEEM in the rainy season was evidently higher in fluorescence intensity compared with those in winter and summer. The position of Peak C in Region V (Figure 8(c)) suggested that humic-like substance has decreased along the canal in the rainy reason. This behavior could be due to the turbulent flow at Sam Lae station causing disruptive sediments and thus higher DOM in the water at the beginning. Then sedimentation occurred as water flowed along the canal, and those sediments could adsorb humic substances as they settled. It is also possible that natural degradation along the canal caused this decrease in humic substance.

In contrast, ΔEEMs in winter and in summer (Figure 8(f) and 8(i)) in Region V were less in magnitude, suggesting that only a small amount of humic substance was reduced during winter and summer. Even though EEMs in summer show more microbial by-product-like substances (Region IV) presented in water samples, ΔEEM in summer did not have any noticeable peaks in Region IV. This result suggested that any physical sedimentation and natural degradation had less impact on microbial by-product-like DOM.

Figure 8

Calculation scheme of ΔEEM from Sam Lae station (A1) and the intake to the MWA WTP (A23).

Figure 8

Calculation scheme of ΔEEM from Sam Lae station (A1) and the intake to the MWA WTP (A23).

In summary, fluorescence EEM measurement is an optical approach that can be used to determine the quantitative and qualitative change of DOM, especially when ΔEEM was calculated. The sensitivity of EEM measurement allows us to quantify a small change that could not be detected with the commonly used parameters like DOC and SUVA.

CONCLUSIONS

This study presents the quantification and characterization of DOM and humic substances along the 18 kilometres of the raw water canal intake to a water supply plant in Bangkok through the year. We investigated DOM properties using DOC, HA, SUVA, and fluorescence EEM. An approach of ΔEEM calculation was applied to track changes of precursors along the canal. Our results and discussion support the following main conclusions.

Concentration of precursors in the canal was seasonally fluctuating, especially from rainfall. During a year of sample collection, DOC was in the range 0.27–6.72 mgC/L and HA was in the range 0.16–4.44 mgC/L. The high HA/DOC ratio of this water indicated that humic substances or the hydrophobic fractions made up the majority of DOM in this water source. The water also had high SUVA (>4 Lmg−1m−1), which indicated high THM formation potential.

Composition of DOM was mainly hydrophobic, aromatic compounds. Among the three seasons, the rainy season had the highest RFI due to algal growth and contamination from surface runoff. The rainy season was also the only season that had spatial variation of DOM with the decrease of humic-like substance (Region V) as water flowed along the canal. DOM composition changes were more pronounced in summer with the presence of microbial by-product-like substances, while geographical variation of DOM was minor along the 18 kilometres of the canal. Based on the results, the quality of the water source for Bangkhen WTP could be improved by preventing the additional organic loading from rainfall. Because flooding is common in Bangkok, a closed system water canal might be necessary to present contamination from surface runoff in the rainy season.

Even though THM concentration in the treated water from Bangkhen WTP does not exceed the standard of WHO, understanding of the spatial and seasonal variation of precursors, especially the humic substances, can ensure good water treatment strategies before the chlorination process. The sensitivity of EEM measurement allows quantification of a small change that could not be detected with the commonly used parameters like DOC and SUVA. The results of this study provide an insight into the prediction of humic acid in source water, which benefits the MWA of Thailand in being aware of seasonal variation in water quality.

ACKNOWLEDGEMENTS

The authors thank the Departments of Environmental Engineering, Kasetsart University and the Metropolitan Waterworks Authority (MWA), Bangkok, Thailand. The collaboration with the Civil Engineering Department, Tokyo Institute of Technology, Japan, and the Japan Society for the Promotion of Science (JSPS) is also greatly appreciated. Most of all, we would like to thank the National Research Council of Thailand (NRCT) for the funding support.

REFERENCES

REFERENCES
Aschermann
G.
,
Jeihanipour
A.
,
Shen
J.
,
Mkongo
G.
,
Dramas
L.
,
Croué
J.-P.
&
Schäfer
A.
2016
Seasonal variation of organic matter concentration and characteristics in the Maji ya Chai river (Tanzania): impact on treatability by ultrafiltration
.
Water Research
101
,
370
381
.
Bridgeman
J.
,
Bieroza
M.
&
Baker
A.
2011
The application of fluorescence spectroscopy to organic matter characterisation in drinking water treatment
.
Reviews in Environmental Science and Bio/Technology
10
,
277
290
.
Chen
W.
,
Westerhoff
P.
,
Leenheer
J. A.
&
Booksh
K.
2003
Fluorescence excitation–emission matrix regional integration to quantify spectra for dissolved organic matter
.
Environmental Science & Technology
37
(
24
),
5701
5710
.
Krasner
S. W.
,
Weinberg
H. S.
,
Richardson
S. D.
,
Pastor
S. J.
,
Chinn
R.
,
Sclimenti
M. J.
,
Onstad
G. D.
&
Thruston
A. D.
2006
Occurrence of a new generation of disinfection byproducts
.
Environmental Science & Technology
40
(
23
),
7175
7185
.
Krasner
S. W.
,
Westerhoff
P.
,
Chen
B.
,
Rittmann
B. E.
,
Nam
S.-N.
&
Amy
G.
2009
Impact of wastewater treatment processes on organic carbon, organic nitrogen, and DBP precursors in effuent organic matter
.
Environmental Science & Technology
43
(
8
),
2911
2918
.
Kueseng
T.
,
Suksaroj
T. T.
,
Musikavong
C.
&
Suksaroj
C.
2011
Enhanced coagulation for removal of dissolved organic matter and trihalomethane formation potential from raw water supply in Sri-Trang reservoir, Thailand
.
Water Practice and Technology
6
(
1
), wpt2011002.
Lavonen
E. E.
,
Kothawala
D. N.
,
Tranvik
L. J.
,
Gonsior
M.
,
Schmitt-Kopplin
P.
&
Köhler
S. J.
2015
Tracking changes in the optical properties and molecular composition of dissolved organic matter during drinking water production
.
Water Research
85
,
286
294
.
Libecki
B.
&
Dziejowski
J.
2008
Optimization of humic acids coagulation with aluminum and iron(III) salts
.
Polish Journal of Environmental Studies
17
(
3
),
397
403
.
Matilainen
A.
,
Vepsäläinen
M.
&
Sillanpää
M.
2010
Natural organic matter removal by coagulation during drinking water treatment: a review
.
Advances in Colloid and Interface Science
159
,
189
197
.
Matilainen
A.
,
Gjessing
E. T.
,
Lahtinen
T.
,
Hed
L.
,
Bhatnagar
A.
&
Sillanpää
M.
2011
An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment
.
Chemosphere
83
,
1431
1442
.
Musikavong
C.
,
Wattanachira
S.
,
Nakajima
F.
&
Furumai
H.
2007
Three dimensional fluorescent spectroscopy analysis for the evaluation of organic matter removal from industrial estate wastewater by stabilization ponds
.
Water Science and Technology
55
(
11
),
201
210
.
https://doi.org/10.2166/wst.2007.361
.
Panyapinyopol
B.
,
Marhaba
T. F.
,
Kanokkantapong
V.
&
Pavasant
P.
2005
Characterization of precursors to trihalomethanes formation in Bangkok source water
.
Journal of Hazardous Materials
120
,
229
236
.
Plewa
M. J.
,
Muellner
M. G.
,
Richardson
S. D.
,
Fasano
F.
,
Buettner
K. M.
,
Woo
Y.-T.
,
McKague
A. B.
&
Wagner
E. D.
2008
Occurrence, synthesis, and mammalian cell cytotoxicity and genotoxicity of haloacetamides: an emerging class of nitrogenous drinking water disinfection byproducts
.
Environmental Science & Technology
42
(
3
),
955
961
.
Singer
P. C.
,
Schneider
M.
,
Edwards-Brandt
J.
&
Budd
G. C.
2007
MIEX for removal of DBF precursors: pilot-plant findings
.
Journal American Water Works Association
99
(
4
),
128
139
.
US Environmental Protection Agency
2001
National Primary Drinking Water Regulations: Stage 1 Disinfectants and Disinfection Byproducts Rule
.
EPA 816-F-01-014, USEPA, USA
.
Weishaar
J. L.
,
Aiken
G. R.
,
Bergamashi
B. A.
,
Fram
M. S.
,
Fujii
R.
&
Mopper
K.
2003
Evaluation of specific ultra-violet absorbance as an indicator of the chemical content of dissolved organic carbon
.
Environmental Chemistry
37
,
4702
4708
.