Walkerton Clean Water Centre. University of Waterloo

Transcription

1 Xiaohui Jin 1, Victoria Colling 1, Sigrid Peldszus 2, Souleymane Ndiongue 1 1 Walkerton Clean Water Centre 2 University of Waterloo

2 Introduction Increasing cyanobacterial blooms in Ontario. Climate change: water temperature Nutrient enrichment Reference: Winter et al.,

3 Concern Increasing concern about the health effects of cyanobacterial blooms and their toxins in surface and drinking water. About 70% blooms are potentially toxic and pose a risk to human and animals Causing technical challenges for water treatment 3

4 Cyanotoxins Cyanobacteria cells produce taste and odour compounds, and cyanotoxins Microcystins, cylindrospermopsin and anatoxins are most common toxins. Health effects may include adverse impact on nervous system, liver, kidney, tumor promoting effects, carcinogenic potential. 4

5 Regulatory Consideration Emerging Concern US EPA CCL3 Microcystin (hepatotoxin) Cylindrospermopsin (cytotoxin) Anatoxin-a (neurotoxin) Regulations 1.5 µg/l for microcystin-lr (Health Canada) 1.0 µg/l for CYN (WHO provisional guideline) 3.7 µg/l for anatoxin-a (Quebec provisional guideline) 5

6 Impact on Water Treatment Excessive head loss in filtration process Shorter filter run time Taste and odour compounds Increased coagulant demand and oxidant demand Disinfection by-products precursors 6

7 Water Treatment Challenge Removal of particulate cyanobacteria Release of intracellular cyanotoxins and removal of soluble extracellular cyanotoxins Treatment effectiveness varies With different cyanotoxins With intracellular and extracellular cyantoxins 7

8 Overview of Treatment Effectiveness Intracellular: DAF, slow sand filtration, conventional treatment, UF, NF Extracellular: Slow sand filtration, NF, activated carbon adsorption, ozonation, chlorination Treatment effectiveness highly dependent on the cyanobacteria and/or cyanotoxin, water quality (ph, NOM, temperature, etc) Reference: Colling et al.,

9 Objectives Evaluate the effectiveness of various oxidation processes in removal of selected cyanotoxins. Estimate CT values for 99% (2-log) cyanotoxins removal at different ph. 9

10 Microcystin-LR (MC-LR) CAS: MW = 950 Cylindrospermopsin (CYN) CAS: MW = 415 Anatoxin-a (ANTX) CAS: MW =

11 Method Second-order Kinetics d[ toxin] dt = k app [ toxin][ oxidant] Integration [ toxin] ln [ toxin] 0 = k app t 0 [ oxidant] dt = k app CT CT Calculation CT = [ toxin] [ toxin] toxin 0 ln 2.3log [ ] 0 [ toxin] = k app k app 11

12 Reaction Rate Constants (ph = 8) Reaction Rate Constant (M -1 s -1 ) 1.E+10 1.E+08 1.E+06 1.E+04 1.E+02 1.E+00 MC-LR CYN ANTX Cl2 NH2Cl O3 AOP MnO4- ClO2 12

13 CT Values Procedure for Disinfection of Drinking Water in Ontario (2006) CT values for inactivation of Giardia cysts at 20ºC. 13

14 Chlorination ANTX (1-log) CT (mg min/l) Giardia (3-log) Giardia (2-log) MC-LR (1-log) MC-LR (2-log) CYN (2-log) ph 14

15 Ozonation 1 Giardia (2-log) Giardia (1-log) CT (mg min/l) MC-LR (2-log) CYN (2-log) ANTX (2-log) ph 15

16 Chlorine Based Oxidation Chloramine and chlorine dioxide are not effective on oxidation of selected cyanotoxins Chlorine is not effective towards anatoxin-a Reaction rate constant is very low (<1 M -1 s -1 ) Chlorine is not effective for MC on higher ph. Removal efficiency decreases at higher ph Disinfection by-products? 16

17 Ozonation Ozone oxidation is effective Reaction rate constants k O3 > 10 5 (M -1 s -1 ) Ozone may undergo direct (O 3 ) and indirect (OH radical) reactions (at higher ph) Direct reactions target unsaturated bonds (in microcystin, cylindrospermopsin and anatoxin-a) Removal efficiency increases at higher ph. 17

18 Advanced Oxidation Process OH radicals are effective at treatment of cyanotoxins Very high reaction rate constants k OH > 10 9 (M -1 s -1 ) % removal depending on OH generation process, and other factors Addition of hydrogen peroxide to UV converts process to an AOP providing viable treatment option on as needed basis 18

19 Permanganate Not effective in removal of CYN Can be effective in treating MC and anatoxin-a Removal efficiency increases at higher ph. 19

20 Proposed CT Values Chlorine (20 C) 2-log Removal Toxin ph MC-LR CYN ANTX Not Effective 20

21 Proposed CT Values Ozone (20 C) 2-log Removal Toxin ph MC-LR CYN ANTX

22 Approach for Water Utilities Switch to alternative water source when blooms or toxins detected? Monitoring is important How: ELISA, LC/MS/MS? When: Continuous, periodic? Apply different treatments for different cyanotoxins and water quality conditions Oxidation before cell removal should be avoided to prevent the release of intracellular toxins 22

23 Conclusions NH 2 Cl and ClO 2 are not effective in removal of cyanotoxins. Chlorine is not effective for anatoxin-a, much higher dose is needed for MC at higher ph Ozonation and AOP are very effective 23

24 Conclusions (Cont d) Chlorine and ozone CT values for 2-log removal of cyanotoxins are proposed. Treatment effectiveness highly dependent on the cyanobacteria and/or cyanotoxin, water quality. Oxidation before cell removal should be avoided during a cyanobacteria bloom event. 24

25 Acknowledgement Many thanks to Victoria (Tory) Colling, Sigrid Peldszus, and Souleymane Ndiongue. 25