destruction of cyanotoxin microcystin-lr by uv/chlorine ... · reaction rate increases linearly...
TRANSCRIPT
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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
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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
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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.
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http://epa.ohio.gov/habalgae.aspx#147744472-basics
Finished Water
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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
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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
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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
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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.
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[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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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.