The effects of UV disinfection on drinking water quality in distribution systems

Division of R&D for Water, Waterworks Research Institute, Seoul Metropolitan Government, 552-1, Chunho Daero, Kwangjin-Ku, Seoul, Republic of Korea, 143-820.
Water Research (Impact Factor: 5.53). 09/2009; 44(1):115-22. DOI: 10.1016/j.watres.2009.09.011
Source: PubMed
ABSTRACT
UV treatment is a cost-effective disinfection process for drinking water, but concerned to have negative effects on water quality in distribution system by changed DOM structure. In the study, the authors evaluated the effects of UV disinfection on the water quality in the distribution system by investigating structure of DOM, concentration of AOC, chlorine demand and DBP formation before and after UV disinfection process. Although UV treatment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV(254,) SUVA(254), the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular weight) significantly, the increase of low molecular fraction was observed after UV treatment, in dry season. Chlorine demand and THMFP are also increased with chlorination of UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights of broken DOM are not low enough to be used directly by microorganisms in distribution system. Nonetheless, modification of DOM structure can affect water quality of distribution system as it can increase chlorine demands and DBPs formation by post-chlorination.

Full-text

Available from: Young-June Choi, Apr 04, 2014
The effects of UV disinfection on drinking water quality
in distribution systems
Yonkyu Choi, Young-june Choi*
Division of R&D for Water, Waterworks Research Institute, Seoul Metropolitan Government, 552-1, Chunho Daero, Kwangjin-Ku, Seoul,
Republic of Korea, 143-820
article info
Article history:
Received 27 May 2009
Received in revised form
30 August 2009
Accepted 2 September 2009
Published online 16 September 2009
Keywords:
UV
Distribution system
Molecular weight
AOC
Chlorine demand
DBP
abstract
UV treatment is a cost-effective disinfection process for drinking water, but concerned to
have negative effects on water quality in distribution system by changed DOM structure. In
the study, the authors evaluated the effects of UV disinfection on the water quality in the
distribution system by investigating structure of DOM, concentration of AOC, chlorine
demand and DBP formation before and after UV disinfection process. Although UV treat-
ment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV
254,
SUVA
254
, the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular
weight) significantly, the increase of low molecular fraction was observed after UV treat-
ment, in dry season. Chlorine demand and THMFP are also increased with chlorination of
UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights
of broken DOM are not low enough to be used directly by microorganisms in distribution
system. Nonetheless, modification of DOM structure can affect water quality of distribution
system as it can increase chlorine demands and DBPs formation by post-chlorination.
ª 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Disinfection by ultraviolet light (UV) is considered as a cost-
effective and easily implementable system for drinking water
disinfection. Interest in UV disinfection process has been
increased sharply in drinking water industry, since
researchers demonstrated that even very low dosage of UV
light could inactivate Cryptosporidium effectively in the late
1990s (Bukhari et al., 1999; Clancy et al., 2000).
UV spectrum is divided into four regions; vacuum UV
(100w200 nm, hereafter VUV), UV-C (200w280 nm), UV-B
(280w315 nm), and UV-A (315w400 nm). UV disinfection
primarily occurs due to the germicidal action of UV-B and UV-
C light on microorganisms. Although VUV can disinfect
microorganisms, it is not efficient to use VUV for water
disinfection because it rapidly dissipates through water in
very short distances (EPA, 2006). VUV is also known to
breakdown bonds of organic carbons (Buchanan et al., 2004;
Thomson et al., 2004).
Two UV systems are generally applied for drinking water
disinfection process. Monochromatic low pressure UV (here-
after LPUV) emits single wavelength at 254 nm which is close
to the maximum microbial action spectrum. Polychromatic
medium pressure UV (hereafter MPUV) emits a wide range of
wavelength including UV-A, -B, -C and visible light. Special
LPUV emitting two wavelengths at 185 and 254 nm (hereafter
LPUV for TOC) is applied to remove TOC for producing ultra-
pure water.
Although these UV systems are inactivate most of
microorganisms effectively except for some viruses, they
can not guarantee biological safety of tap water because the
effect of UV irradiation can not be maintained throughout
* Corresponding author. Tel.: þ82 2 3146 1810; fax: þ82 2 3146 1811.
E-mail address: membrano@korea.kr (Y.-j. Choi).
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
0043-1354/$ see front matter ª 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2009.09.011
water research 44 (2010) 115–122
Page 1
distribution s ystem. On the contrary, UV d isinfection is
concerned to hav e negative effects on wate r quality by UV
photolysis. Many researchers have reported that UV irradi-
ati on can modif y DOM stru cture and increase biod egrad-
ability (Frimmel, 1998; Thomson et al., 2004; Buchanan et al.,
2005; Goslan et al., 2006). Especially, VUV irradiation is
known to be more effective than UV-C irradiation in
formation of biodegradable compounds and mineralization
(Buchanan et al., 2004). UV-A and U V-B can also splits large
NOM mol ecules into organic acids with lower molecular
weight (Frimmel, 1998). This change of DOM structure can
increase biodegradability, which stimulates m icro bial re-
growth and biofilm formation in distribu tion system.
Increase of biofilm can also cause taste and odor problems
and reduc tion of hydraulic capacity (Shaw et al., 2000).
Therefore, sequentia l disinfect ion process with additional
chemical disinfectant such as chlorine or monochloramine
was applied to prevent m icrobial re-growth in the distribu-
tion system. With chlorination as secondary disinfection
process, UV treatment is often expected to reduce chlorine
demand and DBPs formation. Liu et al. (2006),however,
reported that the DBPs f ormation of four organic waters was
increased by chlorination after UV i rradiation.
The effect of UV irradiation on water quality depends on
many factors, such as characteristics of source water
quality, UV wavelength and a pplied dosage. Previous studies
have often been carried out under bench-scale conditions,
and organic water with relatively high DOC level
(5w17.4 mg/L) and high UV dosage of 14w1,000 J /cm
2
were
used, which were not the conditions used for drinking water
disinfection process (Frimmel, 1998; Buchanan et al., 2006;
Goslan et al., 2006; Liu et al., 2006). Under drinking water
with low D OC level less than 2 mg/ L and UV dosage less than
40 mJ/cm
2
, the impact of UV irradiation on water quality
could be differen t f rom the results of the previous stud ies.
Moreover, the results under lab scale bench test can hardly
reflect the real reactions under full-scale continuous flow
system.
In this study, the authors used pilot-scale continuous flow
UV systems with LPUV, LPUV for TOC, and MPUV, and inves-
tigated change of DOM structure, probability of microbial re-
growth, chlorine demand and THMs formation before and
after UV treatment to evaluate the effects of UV disinfection
on water quality in distribution system.
2. Materials and methods
In this study, the characteristics of DOM, biological re-growth
potential, chlorine demand, and formation potential of
disinfection byproducts before and after UV irradiation were
compared to evaluate the effects of UV disinfection on water
quality in distribution system. A UV pilot plant was installed
at a water treatment plant (WTP) in Seoul, Korea. The samples
were taken three times in 2005 and 2006, considering seasonal
variation of the raw water quality ; 1) dry season with high
algal biomass and BOD from winter to spring, 2) rainy season
with high turbidity due to heavy rainfall during summer, and
3) normal times (Fig. 2).
2.1. UV pilot plant
The UV pilot plant with four UV reactors, LPUV (L85), LPUV for
TOC (L90), MPUV (M1300, M350), is installed at the end of sand
filters in the WTP. Sand filtered water (SF) was introduced to
the reactors, and total capacity of the system was 1080 m
3
/
day. The experiments were carried out with UV dose of
40 mJ/cm
2
, which was usually applied for drinking water
disinfection process. LPUV for TOC (L90) emitting two wave-
lengths at 185 and 254 nm is installed to evaluate TOC removal
efficiency of vacuum UV. As higher UV dosage is required for
TOC mineralization, additional experiments were carried out
with UV dose of 150 mJ/cm
2
.
UV dosage of each reactor was calculated from UV inten-
sity by online sensor and contact time at each flow rate.
Online sensor of LPUV (L90 and L85) and MPUV (M1300 and
M350) can measure at 254 nm and between 200w300 nm,
respectively. L90 system emits UV light with 254 nm and
185 nm with the ratio of 3:1. The detailed characteristics of
each system were listed in Table 1. The sand filtered water and
the five UV treated waters were investigated. The samples
were taken from both the inflow and outflow of each reactor.
2.2. Analytical method
The samples taken from the pilot plant were brought to the
laboratory in 2 h and stored in the refrigerator below 4
C. For
analyses of THMs already formed by pre-chlorination, ascorbic
acid and HCl (1 þ 1) was added instantly to the samples (40 mL)
to quench residual chlorine. For THMFP analyses, the samples
were chlorinated (TOC : chlorine ¼ 1: 3) and incubated at 25
C
for 48 h. After incubation, residual chlorine was quenched with
ascorbic acid and HCl (1 þ 1) not to form THMs any more. THMs
were analyzed by purge and trap method with GC (Varian,
CX3600) equipped with ECD detector according to the EPA 502.2
(EPA, 1995). DOC and UV
254
were analyzed with TOC analyzer
(Ionics,Sievers 820) and UV/VISspectrophotometer(VarianCary
3C), respectively. SUVA
254
was calculated from DOC and UV
254.
2.3. Separation of hydrophilic and hydrophobic carbon
DOM was separated into hydrophobic and hydrophilic frac-
tions with resin (Amberitic XAD-7HP, Rohm & Haas Co.,
Table 1 The characteristics of the UV system in the pilot
plant.
System Lamp type Wavelength of UV
emission (nm)
Capacity
(m
3
/h)
Dosage
(mJ/cm
2
)
L90-4 90 W Low
pressure
for TOC
185, 254 180 40
L90-15 50 150
M1300 1.3 kW
Medium
pressure
185w400 650 40
L85 85 W Low
pressure
254 120
M350 350 W
Medium
pressure
200w400 260
water research 44 (2010) 115–122116
Page 2
France). Resin was cleaned with sequential soxhlet extraction
method (Ma et al., 2001). XAD-7HP resin was packed in 31 mm
(ID) 230 mm (H) glass column and 0.5 N NaOHwas introduced
into the column to clean the resin. The resin was extracted
sequentially with methanol, acetonitrile, and methanol for
12 h. Finally, the column was rinsed with ultrapure water, 0.1 N
NaOH, 0.1 N HCl and ultrapure water in order, until the
concentration of TOC of the effluent was less than 0.1 mg/L.
Each sample was adjusted to pH < 2 by adding (1 þ 1) H
3
PO
4
and
passed through clean glass column with flow rate of
15w20 mL/min. The hydrophobic carbon was the fraction that
adsorbed to the surface of the resin and the carbon that passed
out through the column was determined as hydrophilic frac-
tion. After hydrophilic and hydrophobic fractions were
adjusted pH 7 0.2 with 0.1 N H
3
PO
4
and 0.1 N NaOH, DOC was
analyzed with TOC Analyzer (Ionics, Sievers 820).
2.4. Apparent molecular weight
High performance liquid chromatography-size exclusion
chromatography (HPLC-SEC) was used to fractionate apparent
molecular weight of DOM (Her et al., 2003). Separation by size
exclusion was performed using a TSK-50S (Toyopearl HW SOS,
30 mm resin) column prior to sequential on-line detectors con-
sisting of UV/Visble (SPD-20AD, Shimadzu) and DOC (Modified
Sievers Total Organic Carbon Analyzer 820 Turbo). Mobile
phase solution (pH 6.8 and ionic strength 0.1 M) was made with
4 mM phosphate buffer and 25 mM sodium sulfate. Poly-
ethylene glycols (PEGs, 200 600, 2000, 4000, 8000 dalton)
were used for molecular weight (MW) calibration of chro-
matograms. The pH and ionic strength of each sample were
also adjusted with phosphate buffer and sodium sulfate solu-
tions as similar to the mobile phase as possible before analysis
to maintain constant pH and ionic strength for all samples and
reduce undesirable interactions. Number-averaged MW (M
n
),
weight-averaged MW (M
w
), and polydispersivity (r) were
determined using the following equations. h
i
and M
i
are the
height of HPLC-SEC chromatogram and molecular weight.
M
n
¼
P
n
i¼1
h
i
P
n
i¼1
h
i
M
i
M
w
¼
P
n
i¼1
h
i
M
i
P
n
i¼1
h
i
r ¼
M
w
M
n
2.5. Assimilable organic carbon(AOC)
AOC was analyzed with the method proposed by Kaplan et al.
(1993). AOC is defined as the amount of carbon used as energy
or converted into biomass by bacteria. Two pure-culture
bacterial strains, Pseudomonas fluorescens strain P17 (hereafter,
P17) and Spirillum strain NOX (hereafter, NOX) were used. The
sample was taken in a glass vial baked at 550
C over 2 h and
sodium thiosulfate was added to quench residual chlorine.
The sample was pasteurized at 70
C for 30 min in water
bath, and spiked with P17 and NOX, and incubated at 15
C for
7 days. The incubated sample was taken out, inoculated in
R2A media and incubated at 25
C for 72 h. The colony counts
of P17 and NOX in stationary phase were converted into
bacterial biomass by multiplying each carbon conversion
Table 2 DOC, UV
254
, and SUVA
254
of pre- and post-UV treated water.
System DOC (mg/L) UV
254
(cm
1
) SUVA
254
(L/mg$m)
Normal Dry Rainy Normal Dry Rainy Normal Dry Rainy
SF 0.96 1.26 1.27 0.014 0.015 0.022 1.45 1.19 1.73
L90-4 0.96 1.31 1.27 0.014 0.015 0.022 1.45 1.14 1.73
L90-15 0.96 1.34 1.30 0.013 0.014 0.020 1.35 1.04 1.53
M1300 0.97 1.25 1.24 0.014 0.015 0.022 1.44 1.20 1.77
L85 0.96 1.27 1.24 0.014 0.015 0.022 1.45 1.18 1.77
M350 0.95 1.23 1.23 0.015 0.015 0.020 1.57 1.21 1.62
70 71
72
69
70 71
30
29
28
31 30
29
Normal times
80
78
79
81
80
81
20
22
21
19
20
19
0%
20%
40%
60%
80%
100%
Dry season
65
66
66
65
67
62
35
34
34
35
33
38
SF L90-4 L90-15 M1300 L85 M350
SF L90-4 L90-15 M1300 L85 M350
SF L90-4 L90-15 M1300 L85 M350
Hydrophilic Hydrophobic
Rainy season
Fig. 1 The ratio of hydrophilic and hydrophobic fractions in pre- and post-UV treated water.
water research 44 (2010) 115–122 117
Page 3
factor. P17 AOC and NOX AOC were calculated by the
following equations, and AOC was calculated by the sum of
P17 AOC and NOX AOC.
P17 AOCðmg=LÞ¼
P17ðCFU=mLÞ
4:1 10
6
ðCFU=mgCÞ
1000 mL=L
NOX AOCðmg=LÞ¼
NOXðCFU=mLÞ
1:2 10
7
ðCFU=mgCÞ
1000 mL=L
AOCðmg=LÞ¼P17 AOC þ NOX AOC
2.6. Chlorine demand and decay rate
Chlorine demand and decay rate were estimated for the sand
filtered water and the UV treated water taken from each UV
reactor. Chlorine decay rate was measured with the procedure
proposed by Powell et al. (2000). The freshly cleaned glassware
was filled with distilled water and sodium hypochlorite solu-
tion was added to make 10 mg/L of free chlorine solution and
left for 24 h. It was then emptied, rinsed thoroughly with
ultrapure water and left to dry. 2 L volumetric flask was filled
with ultrapure water and the sample water. Chlorine was
added to 1w 2 mg/L and left for 15 min to ensure homoge-
neity. The sample water was decanted into eleven 125 mL
brown glass bottles without headspace and sealed with teflon
lined caps. All the bottles were stored in the incubator, at 4
and 15
C. The chlorine concentration was measured with
time. Initial chlorine concentration was defined as the chlo-
rine concentration when the same amount of chlorine was
added to 2 L of ultrapure water. Chlorine concentration was
measured by the DPD colorimetric method using Hach pocket
Table 3 Percentage of each fraction of molecular weight in pre- and post-UV treated water of each system.
System >2 K 1–2 K 0.5–1 K <0.5 K M
n
M
w
r
Normal times SF 4.3 17.0 32.1 46.6 750 1574 2.10
L90-4 5.2 17.0 31.3 46.5 766 1558 2.04
L90-15 4.9 17.1 31.6 46.4 771 1581 2.05
M1300 4.5 16.6 31.7 47.2 740 1427 1.93
L85 5.1 17.3 31.6 46.0 773 1547 2.00
M350 4.7 16.0 31.4 47.9 739 1446 1.96
Dry season SF 5.4 15.1 29.0 50.5 744 1627 2.19
L90-4 3.5 14.2 29.8 52.5 736 1640 2.23
L90-15 5.0 14.8 29.0 51.2 671 1246 1.86
M1300 4.1 14.6 29.7 51.6 696 1392 2.00
L85 5.5 15.1 28.6 50.8 756 1709 2.26
M350 4.4 14.7 30.1 50.8 707 1454 2.06
Rainy season SF 1.7 13.2 31.6 53.5 613 979 1.60
L90-4 1.8 13.3 31.4 53.5 602 984 1.63
L90-15 1.5 13.0 31.0 54.5 616 1002 1.63
M1300 1.9 13.5 31.5 53.1 622 1046 1.68
L85 2.1 13.5 31.1 53.3 628 1078 1.72
M350 1.9 13.3 31.2 53.6 619 1033 1.67
M
n
: Number-average molecular weight M
w
: Weight-average molecular weight
BOD, TOC (m
g
/L)
Turbidity (NTU), Rain fall (mm), Chl.a (µg/L)
0
50
100
150
200
250
0
1
2
3
4
5
Turbidity
Rain fall
Chl.a
BOD
TOC
Sampling
Rainy season
Noraml times
Dry seaon
'05 '06
Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun Jul. Aug. Sep. Oct. Nov. Dec.
Month
Fig. 2 Hydraulic characteristics and the raw water quality change by season.
water research 44 (2010) 115–122118
Page 4
chlorine colorimeters (pocket Hachs). All samples were taken
and analyzed in triplicate.
The decay rate constants were estimated by the first-order
chlorine decay model (Jadas-He
´
cart et al., 1992). In this study,
two chlorine decay rates were used, i.e. rapid chlorine decay
rate (K
1
) for the first 4 h and slow chlorine decay rate (K
2
) after
4 h considering the retention time in the clearwell of the WTP.
3. Results and discussions
3.1. Effects of UV treatment on DOM properties
DOC, UV
254
, SUVA
254
, hydrophilic/hydrophobic ratio and
apparent molecular weight before and after UV treatment
were investigated. The DOC concentration of the sand filtered
water was less than 1 mg/L in normal times but increased to
1.5 mg/L in dry and rainy seasons.
There were little change in DOC, UV
254
, and SUVA
254
after
UV treatment throughout all seasons (Table 2). Only in the L90
system, with low pressure lamp for TOC reduction, a little
decrease of UV
254
and SUVA
254
were observed with the UV
dosage of 150 mJ/cm
2
. The reductions might be caused by high
energy of short wavelength at 185 nm and high dosage of
150 mJ/cm
2
. With dosage of 40 mJ/cm
2
, which is usually
applied for drinking water disinfection process in WTP, all UV
systems had no effect on DOC, UV
254
, and SUVA
254.
The ratio of hydrophilic and hydrophobic fractions was
calculated from DOC concentration of each fraction. The
fraction of hydrophilic DOC was relatively high throughout all
seasons with the range of 62w81 %, but hydrophobic fraction
was increased in rainy season (Fig. 1). The source water from
the Han river, has been known to have relatively higher
concentration of hydrophilic organic fraction (Oh et al., 2003;
Kim et al., 2007; Jeong et al., 2007). The ratio of hydrophilic and
hydrophobic fractions can be changed in water treatment
process. The hydrophilic fraction tends to be increased in
treated water as humic material with high SUVA value and
high hydrophobic organic carbon is removed easily by coag-
ulation process (White et al., 1997). It was also reported, from
the previous studies with the Han river as the source water,
that hydrophilic fraction in the settled water was increased
(Oh et al., 2003; Kim et al., 2007). However, there was not
significant difference in the ratio of hydrophilic and hydro-
phobic fractions before and after UV treatment throughout all
seasons. Shaw et al. (2000) also reported that there was little or
no statistical evidence that hydrophilic and hydrophobic
ratios were altered by UV treatment.
Distribution of apparent molecular weight was measured
by HPLC-SEC system with UV and TOC detectors. The molec-
ular weight of most DOM (over 95 %) was less than 2 kDa
(Table 3), and especially DOM fraction between 0.3 and 0.4 kDa
was dominant throughout all seasons. While the distribution
of apparent molecular weight was not changed before and
after UV treatment in normal times and rainy season, there
was increase in low molecular weight fraction around 0.3 kDa
after UV treatment in dry season (data was not shown).
Number-averaged molecular weights (M
n
) and weight-
averaged molecular weight (M
w
) have also shown that average
molecular weight in the post-UV treated water was decreased
in dry season (Table 3). This suggested that DOM structure in
dry season is broken down more easily by UV radiation than
those in other seasons. DOM structure might be related with
the origin of DOM of each season. In aquatic system, the origin
of DOM can be categorized as allochthonous DOM entering
from the terrestrial watershed, and autochthonous DOM
derived from biota (e.g., algae, bacteria) growing in the water
body (Aiken and Cotsaris, 1995).
In Korea, during the rainy season in late summer with lots
of heavy rain, DOC increases because heavy rain washes large
amount of organic carbon from the watershed into river while
in dry season, algal biomass and BOD increases (Fig. 2). This
allochthonous DOM in rainy season is known to be relatively
refractory DOM with high SUVA, high molecule weight, and
hydrophobic properties. In contrast, the autochthonous DOM
is relatively labile, and consists of low SUVA, low molecular
weight, and hydrophilic DOM (Wetzel, 1983; Kitis et al., 2002).
Ma et al. (2001) reported that hydrophilic fraction was
0
50
100
150
200
250
300
350
400
450
SF L90-4 L90-15 M1300 L85 M350
AOC (µg/L)
Normal times Dry season Rainy season
Fig. 3 Seasonal AOC concentration before and after UV
treatment in each system.
Pre-UV P17 AOC (µg/L)
0 100 200 300 400
0
100
200
300
400
0 20 40 60 80 100 120
0
20
40
60
80
100
120
L90-4 (P17)
L90-15 (P17)
M1300 (P17)
L85 (P17)
M350 (P17)
L90-4 (NOX)
L90-15 (NOX)
M1300 (NOX)
L85 (NOX)
M350 (NOX)
equal value line
Pre-UV NOX AOC (µg/L)
Post-UV P17 AOC (µg/L)
Post-UV NOX AOC (
µ
g/L)
Fig. 4 P17 AOC and NOX AOC before and after UV
treatment.
water research 44 (2010) 115–122 119
Page 5
composed of more simple compounds and less complex
mixtures.
Decrease in molecular weight of DOM was shown with L90-
15, M1300 and M350 systems in dry season. The observation
suggested that short wavelength below 254 nm is more
effective to break down the bonds of organic carbons, and
various wavelength of light could be related to degradation of
DOM. It has been reported that UVA (315–400 nm) and UVB
(280–315 nm) splits large DOM molecules to generate lower
molecular weight organic acids (Frimmel, 1998).
3.2. Effects of UV treatment on AOC
Concentration of AOC, indicator of potential biological re-
growth, was investigated before and after UV irradiation. AOC
was measured from increased living biomass of P17 and NOX
spiked in the samples.
AOC of the sand filtered water was 121 mg/L in normal
times when DOC was low. There was difference in AOC levels
of dry and rainy seasons with similar DOC level. AOC in dry
and rainy season were 341 mg/L and 149 mg/L, respectively. The
results can be interpreted that DOM in the dry season was
much more biodegradable than in the rainy season.
Increase of AOC was observed in some cases with L90-15,
M1300, and L85 systems after UV treatment (Fig. 3). However,
it was not possible to determine if the UV irradiation could
affect AOC level, since there was not consistent trend of
increase in each system. AOC after UV exposure was
compared with AOC of the sand filtered water. P17 AOC and
NOX AOC of all UV systems were plotted against a line of equal
value. More P17 AOC data points fell on or above the line than
below, while more NOX AOC data points fell on or below than
above the line (Fig. 4). Paired t-tests were carried out in sepa-
rate group, LPUV (L90-4, L85) and MPUV (M1300, M350). P17
AOC, NOX AOC and AOC of sand filtered water were not
different statistically from those of LPUV (p ¼ 0.557, 0.964,
0.545) and MPUV (p ¼ 0.234, 0.053, 0.386) at 95 percent confi-
dence level. Shaw et al. (2000) reported that UV treatment did
not appear to affect the AOC concentration, but there were
difference in the P17 and NOX data. Only the P17 AOC
concentration substantially increased after UV treatment (p
value ¼ 0.021) while there was little statistical evidence that
UV treatment affected NOX AOC (p value ¼ 0.381).
3.3. Effects of UV treatment on chlorine decay and DBPs
formation
Chlorine demand, chlorine decay rate, THMs and THMFP
concentrations were investigated for the samples before and
after UV treatment to evaluate the effect of UV disinfection on
chlorine demand and DBPs formation in distribution system
with post-chlorination process. The chlorine decay rate was
Table 4 Chlorine demands and chlorine decay rate before and after UV treatment, K
1
: rapid decay rate(< 4 h), K
2
: slow
decay rate(> 4 h).
4
C15
C
Chlorine demands (mg/L) Decay rate (h
1
) Chlorine demands (mg/L) Decay rate (h
1
)
ID 24 h 48 h K
1
K
2
ID 24 h 48 h K
1
K
2
SF 0.10 0.50 0.60 0.52 0.005 0.06 0.32 0.44 0.025 0.004
L90-4 0.09 0.54 0.63 0.57 0.006 0.21 0.50 0.61 0.073 0.005
L90-15 0.22 0.71 0.79 0.73 0.004 0.22 0.55 0.66 0.079 0.006
M1300 0.12 0.56 0.68 0.67 0.005 0.49 0.55 0.060 0.006
L85 0.10 0.51 0.61 0.62 0.005 0.16 0.46 0.58 0.060 0.006
M350 0.11 0.48 0.60 0.57 0.005 0.16 0.49 0.61 0.074 0.006
Time (hrs)
Residual Chlorine (mg/L)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 20 40 60 80 100 120 140 160 180 200
0 20 40 60 80 100 120 140 160 180 200
L90-15
L90-4
M1300
L85
M350
SF
L90-15
L90-4
M1300
L85
M350
SF
4 °C
15 °C
Fig. 5 Chlorine decay trends before and after UV treatment.
water research 44 (2010) 115–122120
Page 6
very rapid just after addition of chlorine and became slower
with time. The rapid and slow decay rates are likely due to
different reactions such as oxidation of inorganic compounds
(rapid) and substitution reactions with DOM (relatively slow).
In this study, the chlorine consumption in 15 min, 24 h and
48 h were defined as instant demand (ID), 24-h demand, and
48-h demand, respectively. The experiments were conducted
at 4 and 15
C considering seasonal variation of temperature.
ID, 24-h and 48-h demands were increased in all UV systems
at 15
C while there were not significantly different among the
systems at 4
C except for L90-15 and M1300 systems (Table 4,
Fig. 5). This observation suggested that high energy of UV
modify DOM structure and stimulate to react with chlorine at
higher water temperature. In this study, rapid chlorine decay
rate (K
1
) and slow chlorine decay rate (K
2
) were compared
before and after UV treatment (Table 4). Rapid chlorine decay
rate (K
1
) was increased after UV irradiation while slow chlo-
rine decay rate (K
2
) does not change significantly. This
suggests that UV disinfection increases the initial rapid chlo-
rine consumption within the clearwell, but it can not affect
significantly the slow chlorine decay rate in the distribution
system.
Chlorine consumption increased after UV irradiation can
induce increase of DPBs formation. THMs and THMFP
concentrations were investigated seasonally before and after
UV treatment.
THMs, already formed by pre-chlorination process, were
not removed by UV system. On the contrary, THMFP tended to
increase after UV exposure up to 16.5 %. Especially, high
increases of THMFP were observed in the L90-15 and M1300
systems in summer rainy season (Fig. 6).
Paired t-tests were carried out in separate group, LPUV
(L90-4, L85), MPUV (M1300, M350) and all UV (L90-4, L90-15,
L85, M1300, M350). THMs were not significantly different in all
cases (p > 0.072). THMFP of sand filtered water was statisti-
cally different from those after UV treatment at 95 percent
confidence level (LPUV p ¼ 0.065, MPUV p ¼ 0.039, All UV
p ¼ 0.009). This result suggested that UV disinfection process
can increase concentration of THMs by post-chlorination to
prevent bacterial re-growth in drinking water distribution
system, especially in case of UV system with short wave-
length. Liu et al. (2006) reported that statistically significant
increase in the chloroform, DCAA, TCAA, CNCl formation
from chlorination of four organic waters by UV irradiation.
The impacts from UV exposure were found to be most
significant in chloroform formation, and MPUV formed
slightly more of chloroform than LPUV. The authors attributed
the observation to lower molecular weight organic acids
generated by the broader band of UV light emitted from MPUV.
Buchanan et al. (2006) reported reduction after initial increase
of THMFP by UV irradiation. The initial increase of THMFP at
relatively low dosage is presumably consequence of haloge-
nation of low molecular weight compounds produced by
breakdown of large NOM compounds. But THMFP was reduced
at high dosage, which is thought to be primarily due to
removal of NOM. VUV irradiation reduced THMFP much faster
than UV irradiation, which may be resulted from the faster
mineralization and decrease in precursor due to hydroxyl
radical produced by VUV. This hydroxyl radicals (OH) formed
via water photolysis at 185 nm can mineralize organic matters
(Thomson et al., 2004; White, 1999). The destructive capacity
of OH radical depends entirely upon the rate of reaction
between the OH radicals and the organic substrates. Unfor-
tunately, the reaction rate of OH radical with saturated
organic compounds including chloroform is very slow, so
THMs can not be removed effectively by OH radical (White,
1999).
4. Conclusions
The effects of UV disinfection on the quality of drinking water
in distribution system were evaluated in three aspects, 1)
potential of biological re-growth, 2) chlorine demand and 3)
DBPs formation.
At 40 mJ/cm
2
, the dosage applied for drinking water
disinfection, UV treatment can not significantly affect DOM
characteristics and AOC concentration which is indicator of
biological re-growth in distribution system. Although the
increase of low molecular portion was observed in dry season
in medium pressure and 185 nm emitting low pressure
systems, it did not increase AOC concentration significantly.
The broken DOM is not likely small enough to be used directly
by microorganisms in the distribution system.
The chlorine demands and THMFP were increased after UV
exposure. This observation differs from general expectation
that UV disinfection can reduce post-chlorine demand and
DBP formation. Modification of DOM structure by UV irradia-
tion might stimulate reaction with chlorine, and result in
increase of DBP formation.
0
10
20
30
40
50
60
70
80
90
100
THMFP(ug/L)
Fall winter spring
Summer
0
10
20
30
40
50
60
70
80
90
100
SF L90-4 L90-15 M1300 L85 M350
SF L90-4 L90-15 M1300 L85 M350
THMs(ug/L)
Fall winter spring Summer
Fig. 6 THMs and THMFP of pre- and post-UV treated water.
water research 44 (2010) 115–122 121
Page 7
UV disinfection with low dosage of 40 mJ/cm
2
can not
mineralize DOM, but might split chemical bonds or change the
characteristics of functional groups of DOM. This modification
of DOM structure by UV is likely not to stimulate biological re-
growth and biofilm formation in distribution system, but can
have negative effects on water quality by increase of chlorine
demands and DBP formation with following post-chlorina-
tion, especially in medium pressure and vacuum UV systems.
To guarantee the safety of drinking water from pathogenic
microorganisms and harmful DBPs at the same time, the
processes to reduce the precursors of DBP are required when
considering UV installation.
references
Aiken, G., Cotsaris, E., 1995. Soil and hydrology: their effect on
NOM. J. Am. Water Works Assoc. 87 (1), 36–45.
Buchanan, W., Roddick, F., Porter, N., 2004. Enhanced
biodegradability of UV and VUV pretreated natural organic
matter. Water. Sci. Technol. 4 (4), 103–111.
Buchanan, W., Roddick, F., Porter, N., Drikas, M., 2005.
Fractionation of UV and VUV pretreated natural organic matter
from drinking water. Environ. Sci. Technol. 39, 4647–4654.
Buchanan, W., Roddick, F., Porter, N., 2006. Formation of
hazardous by-products resulting from the irradiation of
natural organic matter: comparison between UV and VUV
irradiation. Chemosphere 63, 1130–1141.
Bukhari, Z., Hargy, T.M., Bolton, J.R., Dussert, B., Clancy, J.L., 1999.
Medium-pressure UV for Oocyst inactivation. J. Am. Water.
Works. Assoc. 91 (3), 86–94.
Clancy, J.L., Bukhari, Z., Hargy, T.M., Bolton, J.R., Dussert, B.W.,
Marshall, M.M., 2000. Using UV to inactivate Cryptosporidium.
J. Am. Water Works Assoc. 92 (9), 97–104.
EPA, 1995. Method 502.2 Volatile organic compounds in water by
purge and trap capillary column gas chromatography with
photoionization and electrolytic conductivity detectors in series.
EPA, 2006. Ultraviolet disinfection guidance manual for the final
long term 2 enhanced surface water treatment rule. Chapter 2,
1–20.
Frimmel, F.H., 1998. Impact of light on the properties of aquatic
organic matter. Envrion. Int 24 (5/6), 559–571.
Goslan, E.H., Gurses, F., Banks, J., Parsons, S.A., 2006. An
investigation into reservoir NOM reduction by UV photolysis
and advanced oxidation processes. Chemosphere 65,
1113–1119.
Her, N., Amy, G., McKnight, D., Sohn, J., Yoon, Y., 2003.
Characterization of DOM as a function of MW by fluorescence
EEM and HPLV-SEC using UVA, DOC and fluorescence
detection. Water. Res. 37, 4295–4303.
Jadas-He
´
cart, A., El Morer, A., Stitou, M., Bouillot, P., Legube, B.,
1992. The chlorine demand of a treated water. Water Res. 26
(8), 1073–1084.
Jeong, Y., Kweon, J., Lee, S., 2007. Characteristics of natural
organic matter (NOM) on Han riv er and criterion of enhanced
coagulation. Journal of the Korean Society of Water and
Wastewater 21 (6), 653–661.
Kaplan, L.A., Bott, T.L., Reasoner, D.J., 1993. Evaluation and
simplification of the assimilable organic carbon nutrient
bioassay for bacterial growth in drinking water. Appl. Environ.
Microbiol. 59 (5), 1532–1539.
Kim, S.E., Gu, Y.H., Yu, M.J., Chang, H.S., Lee, S.W., Han, S.H., 2007.
Characterization of NOM behavior and DBPs formation in
water treatment processes. J. KSWW 21 (4), 395–407.
Kitis, M., Karanfil, T., Wigton, A., Kilduff, J.E., 2002. Probing
reactivity of dissolved organic matter for disinfection by-
product formation using XAD-8 resin adsorption and
ultrafiltration fractionation. Water Res. 36, 3834–3848.
Liu, W., Cheung, L.-M., Yang, X., Shang, C., 2006. THM, HAA and
CNCl formation from UV irradiation and chlor(am)ination of
selected organic waters. Water Res. 40, 2033–2043.
Ma, H., Allen, H.E., Yin, Y., 2001. Characterization of isolated
fractions of dissolved organic matter from natural waters and
a wastewater effluent. Water Res. 35 (4), 985–996.
Oh, H.K., Kim, H.C., Ku, Y.H., Yu, M.J., Park, H., Chang, H.S., 2003.
Characterization and disinfection by-product formation
potential of natural organic matter in drinking water
treatment. J. of KSEE 25 (10), 1252–1257.
Powell, J.C., Hallam, N.B., West, J.R., Forster, C.F., Simms, J., 2000.
Factors which control bulk chlorine decay rates. Water Res. 34
(1), 117–126.
Shaw, J.P., Malley Jr., J.P., Willoughby, S.A., 2000. Effects of UV
irradiation on organic matter. J. Am. Water Works Assoc. 92
(4), 157–167.
Thomson, J., Roddick, F., Drikas, M., 2004. Vacuum ultraviolet
irradiation for natural organic matter removal. J. Water SRT-
Aqua 53, 193–206.
Wetzel, R.G., 1983. Limnology, second ed. Saunders College,
Publishing. 487–518, 667–678.
White, M.C., Thompson, J.D., Harrington , G.W., Singer, P.C.,
1997. Evaluating criteria for enhanced coagu lation
compliance. J. Am . Water Works Assoc. 89 (5), 64–77.
White, G.C., 1999. Handbook of Chlorination and Alternative
Disinfectants, fourth ed. A Wiley-Interscience Publication.
1459–1467.
water research 44 (2010) 115–122122
Page 8
  • Source
    • "However, some microorganisms, especially viruses, have a high resistance against UV irradiation [8,9]. Another disadvantage is that UV cannot guarantee safe drinking water if the distribution system is contaminated with even a low number of surviving microorganisms, because UV irradiation does not provide the residual disinfection effect of chemical disinfectants [10]. Practical application of UV disinfection relies on the germicidal ability of UVC and UVB irradiation (λ = 200–260 nm), which damages nucleic acids of microorganisms by absorption of nucleotides, the building blocks of RNA and DNA [11]. "
    [Show abstract] [Hide abstract] ABSTRACT: Ultraviolet (UV) irradiation is a common way to disinfect drinking water, but some virusesare very resistant to UV. Drinking water was disinfected with UV after spiking with MS2 and18 different coliphagesisolated from municipal wastewater effluent. In addition, some coliphageswere disinfected with combined treatment of chlorine/UV orvice versawith UV/chlorine. A UV-doseof 22 mWs/cm2caused less than 2 Log10-reductions of 10 UV-resistant strains, while it caused up to7 Log10-reductionsfor 9 UV-sensitive or intermediate strains. The high dose (117 mWs/cm2) causedonly 3 Log10-reductions in some UV-resistant coliphages, including MS2, which proved to be a goodindicator for viruses in UV-disinfection tests. The combined treatment with 0.1 or 0.5 mg Cl/L (freeCl-dosage 0.04 or 0.2 mg/L, respectively) for 10 min followed by UV irradiation of 22 mWs/cm2inactivated all coliphages tested by >3.6 Log10-units. Synergy was obtained for most coliphagestested by using a Cl/UV combination, and the inactivation using first low Cl-dosages followed bylow UV-dosages was higher than if using high Cl- or UV-dosages alone. The opposite treatment withUV/Cl was less effective. Therefore, the combination treatment using first chlorine and then UV can be recommended as a disinfection method for viruses
    Full-text · Article · Apr 2016
  • Source
    • "No DBPs was observed when no bromide , respectively. Noticeably, The UV dosage used in this study was 1056 mJ/cm 2 which might split chemical bonds or change the characteristics of functional groups of organic matter [29]. However, the UV dosage of each treatment was the same, thus the effect of UVA irradiation on the DBP should be the same for all the treatment. "
    [Show abstract] [Hide abstract] ABSTRACT: The high effectiveness of TiO2-UVA system in bacterial disinfection has gained attention to use this technology in water treatment on different source waters, including desalinated sea water and grey water. However, source waters containing a significant level of bromide could have different chemical pathways during TiO2-UVA disinfection process because reactive bromine species could be formed. To illustrate the water safety from the Br-TiO2-UVA system, this study investigated bacterial inactivation efficiency and disinfection byproduct (DBP) formation under different pH, TiO2 dosages and bromide concentrations in a laboratory setting. At a high bromide concentration (65 mg/L, equivalent to the concentration of natural sea water), the bacterial inactivation rate increased 2 times at pH 5 and more than 5 times at pH 8. However, a significant increase of brominated DBPs, which were considered more carcinogenic and toxic than chlorinated DBPs, was observed. The bacterial inactivation pattern was shifted from the “shoulder-log” to the “log-tail” under different bromide concentrations, suggesting the existence of bromide altered the bacterial inactivation mechanisms. We also observed that the inactivation kinetics of Br-TiO2-UVA system was greatly influenced by water pH. Our laboratory experiments demonstrated that bromide could improve the performance of photocatalytic inactivation, but it also could reduce the water safety by generating a higher level of brominated-DBPs in treated water. Water engineers should pay attention to the brominated DBP formation when applying TiO2-UVA photocatalysis on source waters with a significant level of bromide.
    Full-text · Article · Mar 2016
  • Source
    • "The combined UV/PS efficiency was 91%. The results obtained from two processes of UV alone and PS alone were in line with results of literatures that showed these two processes decreased pollutants insubstantially [18,32]. For example, Gao et al. used UV/PS to remove sulfamethazine from aquatic solutions. "
    [Show abstract] [Hide abstract] ABSTRACT: This study investigated the degradation of phenol at high concentrations from saline wastewater using UV/Persulfate (UV/PS) in a bench scale reactor. The effect of operational variables such as PS concentration (50, 80, 100, 150, and 200 mM), solution pH (3, 7, and 10), initial phenol concentration (200, 450, 1,000, 1,500, and 2,000 mg/L), and NaCl concentration (30,000, 50,000, and 70,000 mg/L) were surveyed. The results revealed that maximum removal of phenol (91%) was obtained after 60 min of reaction at PS molar concentration of 150 mM. Also, changes in pH values had no significant effect on removal efficiency and had slightly greater removal at acidic pH, so pH 3 was selected as optimum. Phenol removal efficiency was increased from 91 to 93% with an increase in the NaCl concentration from 30,000 to 70,000 mg/L, respectively. In addition, phenol removal percentages decrease with an increase in the initial phenol concentration. Efficiency of PS and UV photolysis were 30 and 21%, respectively. The results showed that UV/PS process could be optimally used to remove phenol from saline wastewater and could be effective, economically and environmentally.
    Full-text · Article · Sep 2015 · Desalination and water treatment
Show more