Optimization of Permanganate Pretreatment of Drinking Water to Reduce Microcystin Toxicity. A study to optimize pretreatment

Transcription

1 Optimization of Permanganate Pretreatment of Drinking Water to Reduce Microcystin Toxicity A study to optimize pretreatment

2 Pretreatment of water sources As water is drawn from surface sources it is often pretreated with oxidants to control taste and odor compounds and to suppress invasive mussels. Potassium permanganate is a selective oxidant used for preoxidative treatment. KMnO4 Addition

3 The Problem: Microcystins (MCs) Found in thylakoid stacks in Cyanobacteria Generally intracellular (50-90%)-- depends on cell health Released after cells are damaged Inhibits Protein Phosphatase (PP1 and PP2a) in liver cells (Toxicity) May not be completely removed by conventional water treatment processes

4 Microcystin Overview Microcystins are the most common cyanotoxins found in freshwater Produced by several cyanobacterial genera including Microcystis, Anabaena, and Planktothrix >100 different microcystin congeners have been identified Howard and Boyer (2007) O Neil et al., (2012)

5 The KEY Permanganate oxidation occurs at the C-C double bonds. And maybe here Y X Microcystin X pos. Y pos. MC-LA Leucine Alanine MC-LR Leucine Arginine MC-RR Arginine Arginine MC-YR Tryptophan Arginine

6 Common Congeners LR, YR, RR, LF, LW, dm-lr, and LA LR and LA are the most toxic Most studies have focused on MC-LR We chose to focus on LA

7 Organic Chemistry KMnO4 selectively oxidizes carbon atoms if they contain sufficiently weak bonds, including: Carbon atoms with ππ bonds, as in alkenes and alkynes Carbon atoms with weak C-H bonds, such as: - C-H bonds in the alpha-positions of substituted aromatic rings C-H bonds in carbon atoms containing C-O bonds: -alcohols and aldehydes Carbons with exceptionally weak C-C bonds such as: - C-C bonds in a glycol - C-C bonds next to an aromatic ring AND an oxygen

8 Expressed in two major projects

9 Variables of Interest Concentration Temperature Competition e.g. Natural Organic Matter Degradation of Microcystis cells Environmental factors influence blooms Toxicity of Final Products

10 Lab Experiments (Carus Project) Bench-top experiments Using DI water Manipulating temperature, ph, presence of cells, etc.

11 Lab Experiment Objectives Determine rate constant and kinetic information for MC-LA permanganate oxidation Determine the temperature dependence of MC oxidation with permanganate Look at the effects of ph, NOM, etc. Establish a pattern or model based the rate constants that can be used by operators at water treatment plants for more effective treatment

12 Harmful Algal Bloom (HAB) project 30+ Lakes from July to October Brief environmental survey Water samples once a month and SPATT bags for time in between Analytical methods of real aquatic samples

13 HAB Project Objectives Look at environmental factors and how land use influences microcystin presence Look at the distribution of congener types across Michigan Test validity of microcystin assays like the ELISA

14 Laboratory procedures, sample collection, storage, preparation for analysis

15 Kinetic Experimental Materials Milli-Q DI Water Microcystin LA and LR 4 place mini-mix jar tester Potassium Permanganate Sodium Thiosulfate

16 Kinetic Experimental Method Permanganate solution was standardized using sodium oxaloacetate Sodium oxaloacetate in acidic solution Warmed solution between C Oxaloacetate titrated with permanganate solution Concentration in ppm determined by mg KMnO4 L = (g oxaloacetate) (Volume titrant in ml) Pic: UW-Madison Chemistry

17 Kinetic Experimental Method Using quartz cuvette Determined concentration of MC using A 238 [MC] = A L mol cm 1cm Find volume needed to spike M1V1 = M2V2

18 Kinetic Experimental Method Spiked DI and natural water samples with a known concentration of MC by A 238 Take initial sample Permanganate was added (concentrations realistic to treatment, usually 2 ppm) Take timed samples quench with excess sodium thiosulfate to stop reaction Vortex then spin down to eliminate any MnO2

19 Kinetic Experimental Method Use LC/TOF to identify and determine concentration of unreacted MCs H2O acetonitrile gradient w/ 0.1% formic acid Use peak integration to determine relative abundance Determine concentrations based on (Initial concentration) Area at time t Area of initial peak

20 Rate Constants Kinetics are second order overall Rate =k[mc][kmno4] Simpler experiment if excess of KMnO4 is used but a concentration that is realistic to treatment plants Rate constant can be calculated using pseudo-first order kinetics ln [MC] [MCo] = k t where k = k[mno 4 ] Plot ln [MC] [MCo] vs t where: -slope = psuedo rate constant

21 Data analysis Spies and Szlag, 2016

22 Temperature Dependence Arrhenius equation k = Ae Ea/(RT) Where Ea is the activation energy R is the ideal gas constant (8.314 J/mol) T is temperature (Kelvin) A is the pre-exponential factor Linearize ln k = ln A Ea R Plot ln k vs. 1/T 1 T

23 Calculating the Ea Ea = kJ/mol Ea = kJ/mol Slope J mol = Ea

24 HAB Project Method Characterization of lake Samples taken from 30+ lakes across Michigan by filling PETG vials 20 cm below surface Freeze thawed 3 times to lyse cells Filtered using plate filter Triple Quadrupole MS/MS at WSU Dilution with H2O to run ELISA

25 Rate constants, competition from NOM, etc. Determined by two different projects

26 Rate Constants- no competition Rate constants follow the trend: RR > LR > LA RR LR LA Our work 469 > 339 > 105 M -1 s -1 Rodriguez et al. (2007) 418 > 357 > N/A M -1 s -1 Chen et al. (2005) 469 What is the explanation? Number of potential reactive sites follows this trend: RR=5 >LR=4 > LA=3 RR has two guanidine sites, LR has one guanidine site It is plausible, but not definitive

27 Results MC-LA MC-LR Temp (C) nd order rate constant k (M -1 s -1 ) 54 ± ± ± ± ± ± 98 Ea (kj/mol) 23 ± ± 3.3 MC-LR: good agreement with Rodriguez et al. (2007) k= 357 M -1 s -1 Ea= 28.8 kj/mol

28 KMnO 4 Demand in Lake water Lake water was shown to have a significant demand for permanganate Lake water did not have any statistically relevant effect on the oxidation of MC

29 Competition with cells O cells 2 ppm KMnO4 30,000 cells 2 ppm KMnO4 150,000 cells 2 ppm KMnO4 150,000 cells 0 ppm KMnO A possible trend but not statistically significant Rate constants

30 Data did not show that the presence of cells in permanganate solution lead to cell lysis and a MC spike. This is likely because the lower concentrations made to mimic real treatment applications are not sufficient for the damage needed to destroy them. Experiments with lysed cells did not show any significant effects on MC oxidation or permanganate demand Cell Lysis

31 Toxicity of Final products PPIA was used to determine if there would still be inhibition of phosphatase from products Results show that products had little to no inhibition of phosphatase PP2a

32 HAB project results MS data did not appropriately line up with ELISA (ELISA was higher) Preliminary data shows PPIA might be more appropriate and correlates better with MS

33 HAB project results Nutrient pollution: total PO4 good indicator of bloom risk (consistent with literature) Shallow, sunny, developed areas more likely to have elevated cyanobacteria levels and higher MC levels MC-LA is common

34 What does the data show and how the data can be used for more effective treatment

35 Implications There can be disparity in the kinetics between congeners such as MC-LA which is one of the most common and dangerous MC-LA is common in Michigan Lakes Temperature can make a considerable difference in the rate of oxidation (LA) Natural waters have a demand for permanganate but lysed cells have little Permanganate at appropriate doses has little effect on live cyanobacteria cells Cyanobacteria cells have little effect on extracellular MC oxidation

36 Applications Permanganate treatment can provide ancillary destruction of extracellular microcystins Treatment at regular concentrations will not cause a MC spike from oxidized cells Temperature, congener type, and permanganate demand all need to be taken into account when treating for MC MC-LA have the lowest rate constant of the common congeners can provide a worst case scenario or a good indicator for how effective a treatment is PO4, water temperature, land use can help develop a risk mapping scenario for recreational waters

37 Plug Flow CT CT is the time dependent concentration of permanganate integrated over time (mg l -1 min) Permanganate is usually added at the intake so plug flow is appropriate [MC] o is the initial MC concentration k App is the second order rate constant with units of mg l -1 min CT ln([ M C ] / [ M C ] o) k App

38 CT (mg L -1 min) for MC-LA CT needed to achieve guidance level of 0.3 ppb MC [MC] o is the initial MC-LA concentration Potassium Permanganate T o C [MC] o

39 What s Next Testing detection methods: ELISA (enzyme-linked immunosorbent assay) Degradation products Degradation product toxicity: PPIA (protein phosphatase inhibition assay) Solid Phase Adsorption Toxin Tracking

40 Dr. Szlag The Carus Company Michigan Department of Environmental Quality Lumigen Center at Wayne State University OU Department of Chemistry

41 It is happening here. Where is here? There are over 11,000 lakes in Michigan

42 Solid Phase Adsorption Toxin Tracking Solid Phase Adsorption Toxin Tracking (SPATT) bags made with HP20 resin Placed into PVC holders submerged in lake Rinsed with DI water Placed into MeOH solution Blown down with N2 and reconstituted with H2O Run MS/MS, ELISA, etc.