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: duanxd@mail.uc.edu

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.