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Destruction of Cyanotoxin Microcystin-LR
by UV/Chlorine Process
OAWWA 78th Annual Conference Cincinnati, Ohio, September 15, 2016
Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, Ohio 45221-0012, USA
Email: [email protected]
Xiaodi DuanAdvisor: Dionysios D. Dionysiou
Harmful algal blooms occur in all types of waters, but those with great concernoccur in fresh waters, such as drinking water reservoirs or recreational waters;
In November 2015, USEPA submitted Algal Toxin Risk Assessment and ManagementStrategic Plan for Drinking Water to Congress;
Cyanobacterial harmful algal blooms can produce cyanotoxins, includingneurotoxins and hepatotoxins.
Cyanobacterial Harmful Algal Blooms
Algae bloom viewed from space, responsible for toxic drinking water in Toledo, Ohio on August 2 2014. Photo: NOAA
http://www.cop.noaa.gov/stressors/extremeevents/hab/current/CC_habs.aspx
Lake Taihu, China
Microcystin-LR (MC-LR)
The most widespread and toxic cyanotoxin.
High chemical stability (cyclic structure)
Very Soluble in water (functional groups)
LD50, MCLR = 50 μg/Kg (mouse bioassay). Strong hepatotoxicity. Even low concentrations chronic MC-LR exposure can induce liver cancer.
The health advisory values issued by EPA:
• 0.3 µg/L for children younger than school age
• 1.6 µg/L for all other ages
HN
COHO
N
O CH2
O
NH
NH
O
CH3
CH3
NH
O
COH
O
CNH
O
O
NH
CHN NH2
O
NH
OCH3
6. iso-Glutamic AcidGlu
7. methyl dehydroalanineMdha
1. AlanineAla
2. LeucineLeu
3. Methyl Aspartic AcidMeAsp4. Arginine
Arg
5. Adda
H. Ufelmann, et al., Toxicology, 293 (2012) 59-67.N.Q. Gan, et al., Chem Res Toxicol, 23 (2010) 1477-1484.Y.F. Fang, et al., Environmental Science & Technology, 45 (2011) 1593-1600.
http://epa.ohio.gov/habalgae.aspx#147744472-basics
Finished Water
Chlorination
Widely used for disinfection;
Residual Chlorine needs to bemaintained in distribution system.
UV-254nm irradiation
Often used for disinfection;
Leaves no residue in water.
UV/Chlorine Advanced Oxidation Process
HOCl/OCl- + hv → Cl• + HO•
(Φ > ~1.0) Watts & Linden, 2007, Water Research, 41: 2871-2878;Feng et al., 2007, J. Environ. Eng. Sci., 6: 277-284.
Low Pressure UV lamps
(λmax @ 254 nm)
UV Collimated Beam
Fluence rate = 0.1 mW/cm2
Time (min)0 5 10 15 20 25 30 35
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
UV Fluence (mJ cm-2)0 50 100 150 200
1 mg/L MC-LR, UV only 1 mg/L MC-LR, Cl2 only1 mg/L MC-LR, UV+Cl2 5 g/L MC-LR, UV+Cl2
Decomposition of MC-LR by UV/Chlorine
Reaction rate increases linearly withhigher chlorine input;
UV/Chlorine lowers the energy andchemical consumption, thus reducesthe risk of DBP formation.
Chlorine Concentration (mg/L)
0 1 2 3 4
k (m
in-1
)
0.0
0.2
0.4
0.6
UV+Cl2Cl2 only
UV irradiation or chlorination alone iscapable to degrade MC-LR slowly;
UV/Chlorine can remove 1 mg/L MC-LRin 16 min, and 5 µg/L of MC-LR in 3 minwith small chlorine dose.
[MC-LR]0 = 1 mg/L; pH = 7.4
[Cl2]0 = 1.5 mg/L; pH = 7.4
Generation of HO• in UV/Chlorine
HOCl/OCl- + hv → Cl• + HO•
(Φ > ~1.0) Watts & Linden, 2007, Water Research, 41: 2871-2878;Feng et al., 2007, J. Environ. Eng. Sci., 6: 277-284.
OHO
OHO
OH
OHO
OHO
HO
Non-Fluorescent FluorescentTerephthalic acid
(TA)2-Hydroxyterephthalic acid
(TAOH)
Wavelength (nm)
400 450 500 550
Fluo
resc
ence
inte
nsity
(a.u
.)
0
500
1000
1500
60 min 32 min 16 min 8 min 4 min 1 min 0 min
Concentration of TAOH (uM)
0 1 2 3 4
Fluo
resc
ence
Inte
nsity
(a.u
.)
0
1000
2000
3000
Generation of HO• in UV/Chlorine compared with UV/H2O2
Chlorine alone doesn’tproduce HO•;
The generation of HO• inUV/chlorine is more efficientthan in UV/H2O2
Chlorine is depleted in 0.5 h,while UV/H2O2 can provideHO• continuously for at least5 h.d[TAOH]/dt = 0.35·kTA+HO•·[TA][HO•]
[HO˙]ss × 10-15 MUV+1.5mg/L Cl2 5.61UV+1.5mg/L H2O2 1.22UV+21.1 µM H2O2 0.611.5mg/L Cl2 ≈ 0
Time (min)0 50 100 150 200 250 300
TAO
H C
once
ntra
tion
(uM
)
0
1
2
3
UV Fluence (mJ cm-2)0 500 1000 1500
UV+1.5 mg/L Cl2 = 21.1 uMCl2UV+1.5 mg/L H2O2 UV+21.1 uM H2O2 1.5 mg/L Cl2
Song, et al., 2012, ES&T, 46: 12608-12615.
[MC-LR]0 = 1 mg/L; [Cl2]0 = 1.5 mg/L; pH = 7.4
Contribution of Radicals for MC-LR Degradation
Reaction rates (M−1s−1) of radical species with tert-butyl alcohol (TBA)
and Nitrobenzene (NB)
Radical TBA NB
HO• 6.0 x108 3.9 x109
Cl• 3.0 x108 ≤ 106
Other reactive chlorine species
negligible negligible
Fang J., Fu Y., & Shang C., 2014, ES&T, 48, 1859-1868
Both HO• and Cl• could react with TBArapidly, but only HO• reacts with NB;
Both HO• and Cl• played an importantrole in MC-LR degradation.
UV Fluence (mJ cm-2)0 50 100 150 200
C/C
00.0
0.2
0.4
0.6
0.8
1.0
Time (min)
0 5 10 15 20 25 30 35
UV onlyUV+Cl2+50mM tert-ButanolUV+Cl2+0.05mM NitrobenzeneUV+Cl2Cl2 only
pH Effects on MC-LR Degradation by UV/Chlorine
The optimum pH is 7.4.
Generation of HO· decreases with pH increasing.
Lower rate at pH 6 may be due to protonation of amino acid.
Lower rate at pH > 7.4 is because of dissociation of HOCl/OCl- (pKa= 7.5): Quantum yield:
HOCl + hv → Cl• + HO• (Φ = 1.45)OCl- + hv → Cl• + O•- (Φ = 0.97)
Consumption of HO• and Cl•
by OCl- is faster than did HOCl.
Acero J., Rodriguez E., Meriluoto J., 2005, Wat Res., 39: 1628-1638.Fang J., Fu Y., & Shang C., 2014, ES&T, 48, 1859-1868 .Zhang X., et al., 2016, ES&T, 50 (14), 7671-7678.
pH
6 7.4 9 10.4
k (m
in-1
)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
[HO
] ss (x
10-1
5 M)
0
2
4
6
8
10
12
14
16
UV+1.5 mg/LCl21.5 mg/ Cl2 only[HO] generation in UV+Cl2
[MC-LR]0 = 1 mg/L; [Cl2]0 = 1.5 mg/L
Effects of NOM on MC-LR Degradation by UV/Chlorine
[NOM]0 = 7.0 mg/L as C; [MC-LR]0 = 1 mg/L; [Cl2]0 = 1.5 mg/L; pH = 7.4
NOM is highly problematic for chlorination.
UV/Chlorine is effective in the presence of NOM.
NOM inhibits the MC-LR removal by UV/Chlorine:
• NOM compete with MC-LR for UV light and radical species;
• NOM reacts with Cl2, so free Cl2 < 0.02 mg/L and total Cl2<0.15 mg/L after reaction.
Time (min)0 10 20 30
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
UV Fluence (mJ cm-2)
0 50 100 150 200
UV only Cl2_7NOM Cl2 UV+Cl2_7NOM UV+Cl2
UV Fluence (mJ cm-2)
0 10 20 30 40
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0 UV-LED/Cl2UV-Conventional/Cl2
Degradation of MC-LR by Chlorine + UV-LED
UV-LED: Instant on/offLow power costLong lifetimeMercury freeHigh flexibility
Conventional UV lamp
UV-LEDλmax = 255 nmFluence rate ≈ 0.03 mW/cm2
[MC-LR]0 = 1 mg/L[Cl2]0 = 1.5 mg/L pH = 7.4
Time (min)
0 5 10 15 20C
/C0-0.2
0.0
0.2
0.4
0.6
0.8
1.0 LED (255 nm)LED (285 nm)LED (365 nm)LED (255, 285, 365 nm)
Degradation of MC-LR by Chlorine + UV-LEDUV-LED (255nm, 285nm, 365nm)
[MC-LR]0 = 1 mg/L[Cl2]0 = 1.5 mg/L pH = 7.4
255nm(UVC)
285nm(UVB)
365nm(UVA)
Peak Wavelength (nm) 256 285.7 366.1Average Intensity (mW/cm2) 0.03 0.118 2470
Pseudo-first order rate constant (cm2/mJ) 7.72×10-2 5.78×10-2 2.00×10-6
Richard Miller Treatment Plant, Greater Cincinnati Water Works (GCWW)
GAC UV Chlorine
[MC-LR]0 = 1 mg/L; [Cl2]0 = 1.5 mg/L
GAC as a pre-treatment improvesdegradation of MC-LR by UV/Chlorinesignificantly;
Another benefit: Residual Cl2 needs tobe maintained in distribution system.
Applications in Water Treatment Plant
Stage pHTOC
(mg/L)Alkalinity
(mg/L)SUVA254
(L mg-1 m-1)Before GAC 7.75 1.62 49 2.09After GAC 7.18 1.27 50 1.27
Before GAC After GAC buffered water
k (m
in-1
)
0.00
0.05
0.10
0.15
0.20
0.25
UV onlyCl2 onlyUV+Cl2
Richard Miller Treatment Plant, Greater Cincinnati Water Works (GCWW)
GAC Chlorine UV
[MC-LR]0 = 1 mg/L; [Cl2]0 = 1.5 mg/L
GAC as a pre-treatment improvesdegradation of MC-LR by UV/Chlorinesignificantly;
Another benefit: Residual Cl2 needs tobe maintained in distribution system.
Applications in Water Treatment Plant
Stage pHTOC
(mg/L)Alkalinity
(mg/L)SUVA254
(L mg-1 m-1)Before GAC 7.75 1.62 49 2.09After GAC 7.18 1.27 50 1.27
Before GAC After GAC buffered water
k (m
in-1
)
0.00
0.05
0.10
0.15
0.20
0.25
UV onlyCl2 onlyUV+Cl2
In Clermont County, OH, HABs on HarshaLake in June 2014 led to public healthadvisories warning against swimming in thelake. In June 2016, around 5 µg/L of MC-LRwas detected.
http://news.algaeworld.org/2015/08/clermont-water-plant-uses-multiple-methods-against-algal-blooms/
Site SiteName TOC(mg/L)
SUVA254 (L mg-1 m-1)
pH
BUOY Harsha Buoy8.91 2.91 9.0
EFLS East Fork Lake at DWTP intake Surface 9.48 2.61 8.9
Applications in Source Water with 5 µg/L MC-LR
In source water, degradation rate by UV/Chlorine decreases;
The addition of UV into chlorination accelerates MC-LR degradation significantly insource water, regardless of sampling location.
Lake Harsha
Time (min)0 5 10 15 20 25 30
C/C
0
0.0
0.2
0.4
0.6
0.8
1.0
UV Fluence (mJ cm-2)0 50 100 150
EFLS-4mg/L Cl2 BUOY-4mg/L Cl2BUOY-UV+4 mg/L Cl2 EFLS-UV+4mg/L Cl2Clean-UV+1.5mg/L Cl2
[MC-LR]0 = 5 µg/L
Reaction Mechanism by UV/Chlorine
HOCl/OCl- + hv → Cl• + HO•
Cl• + H2O → HO• + HCl
HO radical chain:
HO• + RH → R• + H2O
R• + HOCl → RCl + HO•
Cl radical chain:
Cl• + RH → R• + HCl
R• + HOCl → ROH + Cl•
Oliver and Carey, 1977, Environ. Sci. Technol., 11: 893-895.Feng, Smith, and Bolton, 2007, J. Environ, Eng. Sci., 6: 277-284.
45
67
O
cyclo
Only consider Adda group:
HN
COHO
N
O CH2
O
NH
NH
O
CH3
CH3
NH
O
COH
O
CNH
O
O
NH
CHN NH2
O
NH
OCH3
MC-LRC49H74N10O12m/ z =
995.5
6. iso-Glutamic Acid
Glu
7. methyl dehydroalanineMdha
1. AlanineAla
2. LeucineLeu
3. Methyl Aspartic
Acid
MeAsp4. ArginineArg
5. Adda
Radical Attack on Aromatic Ring
Cl• is reactive toward benzene (k = 6×109 M-1 s-1 to1.2×1010 M-1 s-1), benzoic acid and phenol.
m/z =1029.5 has also been detected in chlorination ofMC-LR.
The first hydroxylation or chlorination increases theelectron-density of the benzoic ring therefore thesecond one occurs more easily.
Alegre et al, 2000, J. Phys. Chem., 104: 3117-3125. Tsuji et al, 1997, Toxicon, 35:1033-1041. Antoniou et al., 2008, Environ. Sci. Technol, 42: 8877 -8883.
O
45
67
cyclo
Cl
O
45
67 cyclo
HO
HO
O
45
67cyclo
HO
OHOH
m/z 1029.5
m/z 1027.5
m/z 1045.5
45
67
MC-LR
O
m/z 995.5
O
45
67
cyclo
HO
m/z 1011.5
O
45
67 cyclo
Cl
Cl
m/z 1063.5
cyclo
m/z 1047.5
O
45
67 cyclo
OHCl
Radical Attack on Diene Bonds
Gilbert et al., 1988, J. Chem Soc., Faraday Trans., 84(10): 3319-3330. Antoniou et al., 2008, Environ. Sci. Technol, 42: 8877 -8883.
O
45
67 cyclo
m/ z 1029.5
O
45
67cyclo
OHOH
m/z 1029.5
O
45
67 cyclo
m/ z 1013.5
O
m/ z 1011.5
OH
cyclo
45
67
MC-LR
O
m/z 995.5
cyclo
O cyclo O cyclo
m/z 835.5 m/ z 795.5
O
m/z 1011.5
O
cyclo
Tautomers
O
45
67
cyclo
m/ z 1029.5
OHOH
Cl OH
Summary
UV/chlorine lowers the energy and chemical consumption forMC-LR removal, and is still effective at high pH range and inthe presence of NOM;
UV/Chlorine generates high amount of HO•;
MC-LR degradation rate by UV/Chlorine dramaticallydecreases in source water; the conventional water treatmentprocesses and GAC significantly improved the efficiency;
UV-LED is a promising technology for algal toxin removal;
Diene bonds and aromatic ring of the Adda amino acid in MC-LR are the most susceptible groups to radical attack.
Advisor: Dionysios D. Dionysiou
Collaborators: Heath Mash, Toby Sanan, and Joel Allen fromEPA; Maria Meyer and Jeff Swertfeger from GCWW
The project was supported by a Harmful Algal BloomResearch Initiative grant from the Ohio Department of HigherEducation.
Grants-in-Aid of Research from Sigma Xi Society University ofCincinnati Chapter; Summer Research Fellowship, Richard C.Wigger Scholarship, and John David Eye Scholarship fromUniversity of Cincinnati.
Acknowledgement
Sandusky Bay, Erie County, Ohio. The two largest algal blooms ever recorded on Lake Erie occurred in the past five years. Image courtesy Ohio Sea Grant and Stone Laboratory.