Destruction of Cyanotoxin Microcystin-LR by UV/Chlorine Process

Transcription

1 AWWA 8 th Annual Conference Cincinnati, hio, September 1, 201 Destruction of Cyanotoxin Microcystin-LR by UV/Chlorine Process Xiaodi Duan Advisor: Dionysios D. Dionysiou Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, hio , USA duanxd@mail.uc.edu

2 Cyanobacterial Harmful Algal Blooms Harmful algal blooms occur in all types of waters, but those with great concern occur in fresh waters, such as drinking water reservoirs or recreational waters; In November 201, USEPA submitted Algal Toxin Risk Assessment and Management Strategic Plan for Drinking Water to Congress; Cyanobacterial harmful algal blooms can produce cyanotoxins, including neurotoxins and hepatotoxins. Lake Taihu, China hab/current/cc_habs.aspx Algae bloom viewed from space, responsible for toxic drinking water in Toledo, hio on August Photo: NAA

3 Microcystin-LR (MC-LR) The most widespread and toxic cyanotoxin. High chemical stability (cyclic structure) Very Soluble in water (functional groups) LD 0, MCLR = 0 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. µg/l for all other ages. iso-glutamic Acid Glu CH 3. Adda H HN C. Arginine Arg. methyl dehydroalanine Mdha C N CH 2 C C HN 2 H 1. Alanine Ala CH 3 CH 3 3. Methyl Aspartic Acid MeAsp 2. Leucine Leu H. Ufelmann, et al., Toxicology, 293 (2012) 9-. N.Q. Gan, et al., Chem Res Toxicol, 23 (2010) Y.F. Fang, et al., Environmental Science & Technology, (2011)

4 Finished Water

5 UV/Chlorine Advanced xidation Process Chlorination Widely used for disinfection; Residual Chlorine needs to be maintained in distribution system. UV-2nm irradiation ften used for disinfection; Leaves no residue in water. Low Pressure UV lamps (λ 2 nm) HCl/Cl - + hv Cl + H (Φ > ~1.0) Watts & Linden, 200, Water Research, 1: ; Feng et al., 200, J. Environ. Eng. Sci., : UV Collimated Beam Fluence rate = 0.1 mw/cm 2

6 Decomposition of MC-LR by UV/Chlorine mg/l MC-LR, UV only 1 mg/l MC-LR, Cl 2 only 1 mg/l MC-LR, UV+Cl g/l MC-LR, UV+Cl 2 C/C [Cl 2 ] 0 = 1. mg/l; ph =. k (min -1 ) UV+Cl 2 Cl 2 only [MC-LR] 0 = 1 mg/l; ph = Time (min) Chlorine Concentration (mg/l) UV Fluence (mj cm -2 ) UV irradiation or chlorination alone is capable to degrade MC-LR slowly; UV/Chlorine can remove 1 mg/l MC-LR in 1 min, and µg/l of MC-LR in 3 min with small chlorine dose. Reaction rate increases linearly with higher chlorine input; UV/Chlorine lowers the energy and chemical consumption, thus reduces the risk of DBP formation.

7 Generation of H in UV/Chlorine HCl/Cl - + hv Cl + H (Φ > ~1.0) Watts & Linden, 200, Water Research, 1: ; Feng et al., 200, J. Environ. Eng. Sci., : Fluorescence intensity (a.u.) min 32 min 1 min 8 min min 1 min 0 min H H 0 H H Wavelength (nm) 3000 H Non-Fluorescent Terephthalic acid (TA) H Fluorescent 2-Hydroxyterephthalic acid (TAH) Fluorescence Intensity (a.u.) Concentration of TAH (um)

8 Generation of H in UV/Chlorine compared with UV/H UV+1. mg/l Cl 2 = 21.1 umcl 2 UV+1. mg/l H 2 2 [H ] ss 10-1 M TAH Concentration (um) 2 1 UV+21.1 um H mg/l Cl 2 UV+1.mg/L Cl 2.1 UV+1.mg/L H UV+21.1 µm H mg/L Cl 2 0 Chlorine alone doesn t produce H ; Time (min) The generation of H in UV/chlorine is more efficient than in UV/H UV Fluence (mj cm -2 ) d[tah]/dt = 0.3 k TA+H [TA][H ] Chlorine is depleted in 0. h, while UV/H 2 2 can provide H continuously for at least h. Song, et al., 2012, ES&T, :

9 Contribution of Radicals for MC-LR Degradation Reaction rates (M 1 s 1 ) of radical species with tert-butyl alcohol (TBA) and Nitrobenzene (NB) Radical TBA NB UV only UV+Cl 2 +0mM tert-butanol UV+Cl mM Nitrobenzene UV+Cl 2 Cl 2 only H.0 x x10 9 Cl 3.0 x ther reactive chlorine species negligible negligible C/C Fang J., Fu Y., & Shang C., 201, ES&T, 8, Both H and Cl could react with TBA rapidly, but only H reacts with NB; Both H and Cl played an important role in MC-LR degradation UV Fluence (mj cm -2 ) Time (min) [MC-LR] 0 = 1 mg/l; [Cl 2 ] 0 = 1. mg/l; ph =.

10 ph Effects on MC-LR Degradation by UV/Chlorine The optimum ph is UV+1. mg/lcl2 1. mg/ Cl2 only [H] generation in UV+Cl Generation of H decreases with ph increasing. k (min -1 ) [H] ss (x 10-1 M) Lower rate at ph may be due to protonation of amino acid. Lower rate at ph >. is because of dissociation of HCl/Cl - (pka =.): Quantum yield: ph 0 HCl + hv Cl + H (Φ = 1.) Cl - + hv Cl + - (Φ = 0.9) [MC-LR] 0 = 1 mg/l; [Cl 2 ] 0 = 1. mg/l Consumption of H and Cl by Cl - is faster than did HCl. Acero J., Rodriguez E., Meriluoto J., 200, Wat Res., 39: Fang J., Fu Y., & Shang C., 201, ES&T, 8, Zhang X., et al., 201, ES&T, 0 (1), 1-8.

11 Effects of NM on MC-LR Degradation by UV/Chlorine 1.0 NM is highly problematic for chlorination UV/Chlorine is effective in the presence of NM. C/C UV only Cl 2 _NM Cl 2 UV+Cl 2 _NM UV+Cl 2 NM inhibits the MC-LR removal by UV/Chlorine: NM compete with MC-LR for UV light and radical species; Time (min) UV Fluence (mj cm -2 ) NM reacts with Cl 2, so free Cl 2 < 0.02 mg/l and total Cl 2 <0.1 mg/l after reaction. [NM] 0 =.0 mg/l as C; [MC-LR] 0 = 1 mg/l; [Cl 2 ] 0 = 1. mg/l; ph =.

12 Degradation of MC-LR by Chlorine + UV-LED UV-LED: Instant on/off Low power cost Long lifetime Mercury free High flexibility C/C UV-LED/Cl 2 UV-Conventional/Cl [MC-LR] 0 = 1 mg/l [Cl 2 ] 0 = 1. mg/l ph = UV Fluence (mj cm -2 ) λ max = 2 nm Fluence rate 0.03 mw/cm 2 Conventional UV lamp UV-LED

13 Degradation of MC-LR by Chlorine + UV-LED UV-LED (2nm, 28nm, 3nm) 1.0 LED (2 nm) LED (28 nm) LED (3 nm) 0.8 LED (2, 28, 3 nm) C/C [MC-LR] 0 = 1 mg/l [Cl 2 ] 0 = 1. mg/l ph = Time (min) 2nm 28nm 3nm (UVC) (UVB) (UVA) Peak Wavelength (nm) Average Intensity (mw/cm 2 ) Pseudo-first order rate constant (cm 2 /mj)

14 Applications in Water Treatment Plant Richard Miller Treatment Plant, Greater Cincinnati Water Works (GCWW) GAC UV Chlorine k (min -1 ) UV only Cl2 only UV+Cl2 TC (mg/l) Alkalinity (mg/l) SUVA2 (L mg -1 m -1 ) Stage ph Before GAC After GAC GAC as a pre-treatment improves degradation of MC-LR by UV/Chlorine significantly; 0.00 Before GAC After GAC buffered water [MC-LR] 0 = 1 mg/l; [Cl 2 ] 0 = 1. mg/l Another benefit: Residual Cl 2 needs to be maintained in distribution system.

15 Applications in Water Treatment Plant Richard Miller Treatment Plant, Greater Cincinnati Water Works (GCWW) GAC Chlorine UV k (min -1 ) UV only Cl2 only UV+Cl2 TC (mg/l) Alkalinity (mg/l) SUVA2 (L mg -1 m -1 ) Stage ph Before GAC After GAC GAC as a pre-treatment improves degradation of MC-LR by UV/Chlorine significantly; 0.00 Before GAC After GAC buffered water [MC-LR] 0 = 1 mg/l; [Cl 2 ] 0 = 1. mg/l Another benefit: Residual Cl 2 needs to be maintained in distribution system.

16 Applications in Source Water with µg/l MC-LR Lake Harsha In Clermont County, H, HABs on Harsha Lake in June 201 led to public health advisories warning against swimming in the lake. In June 201, around µg/l of MC-LR was detected. Site SiteName TC (mg/l) BUY Harsha Buoy EFLS SUVA2 (L mg -1 m -1 ) ph East Fork Lake at DWTP intake Surface C/C [MC-LR] 0 = µg/l Time (min) UV Fluence (mj cm -2 ) EFLS-mg/L Cl 2 BUY-mg/L Cl 2 BUY-UV+ mg/l Cl 2 EFLS-UV+mg/L Cl 2 Clean-UV+1.mg/L Cl 2 In source water, degradation rate by UV/Chlorine decreases; The addition of UV into chlorination accelerates MC-LR degradation significantly in source water, regardless of sampling location.

17 Reaction Mechanism by UV/Chlorine HCl/Cl - + hv Cl + H Cl + H 2 H + HCl H radical chain: H + RH R + H 2 R + HCl RCl + H Cl radical chain: Cl + RH R + HCl R + HCl RH + Cl. i so - Glutamic Acid Glu CH 3. Add a MC - LR C 9 H N m/ z = 99. H HN C. A rginine Arg. me thyl dehydroalanine Mdha C nly consider Adda group: N CH 2 C C HN 2 H CH 3 1. Al anine Ala CH 3 3. M ethyl Aspartic Acid MeAsp 2. L eucine Leu liver and Carey, 19, Environ. Sci. Technol., 11: Feng, Smith, and Bolton, 200, J. Environ, Eng. Sci., : 2-28.

18 Radical Attack on Aromatic Ring Cl Cl Cl MC-LR m/z 99. m/z m/z 103. H H H Cl H m/z m/z 102. m/z 10. H H H m/z 10. Cl is reactive toward benzene (k = 10 9 M -1 s -1 to M -1 s -1 ), benzoic acid and phenol. m/z =1029. has also been detected in chlorination of MC-LR. The first hydroxylation or chlorination increases the electron-density of the benzoic ring therefore the second one occurs more easily. Alegre et al, 2000, J. Phys. Chem., 10: Tsuji et al, 199, Toxicon, 3: Antoniou et al., 2008, Environ. Sci. Technol, 2:

19 Radical Attack on Diene Bonds Cl H MC-LR m/z 99. m/ z m/ z H H H H H m/ z m/z m/ z Tautomers m/z m/z 83. m/ z 9. Gilbert et al., 1988, J. Chem Soc., Faraday Trans., 8(10): Antoniou et al., 2008, Environ. Sci. Technol, 2:

20 Summary UV/chlorine lowers the energy and chemical consumption for MC-LR removal, and is still effective at high ph range and in the presence of NM; UV/Chlorine generates high amount of H ; MC-LR degradation rate by UV/Chlorine dramatically decreases in source water; the conventional water treatment processes 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.

21 Acknowledgement Advisor: Dionysios D. Dionysiou Collaborators: Heath Mash, Toby Sanan, and Joel Allen from EPA; Maria Meyer and Jeff Swertfeger from GCWW The project was supported by a Harmful Algal Bloom Research Initiative grant from the hio Department of Higher Education. Grants-in-Aid of Research from Sigma Xi Society University of Cincinnati Chapter; Summer Research Fellowship, Richard C. Wigger Scholarship, and John David Eye Scholarship from University of Cincinnati.

22 Sandusky Bay, Erie County, hio. The two largest algal blooms ever recorded on Lake Erie occurred in the past five years. Image courtesy hio Sea Grant and Stone Laboratory.