Using rapid background hydroxyl radical scavenging measurement to understand OH radical reactivity of NOM in AOPs.

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1 Using rapid background hydroxyl radical scavenging measurement to understand OH radical reactivity of NOM in AOPs. Erik Rosenfeldt, PE, PhD Senior Principal Engineer Hazen and Sawyer Fourth IWA Specialty Conference:NOM: From Source to Tap July 27 29, Costa Mesa, CA

2 Acknowledgements University of Massachusetts Faculty Research Grant Matthew Hross Engineer, Malcolm Pirnie Performed work as an MS Student at the University of Massachusetts, Amherst Zach Monge Staff Engineer, CH2MHill Performed work as an MS Student at the University of Massachusetts, Amherst

3 Agenda Evolution of Scavenging Measurement The R OH,UV concept Using R OH,UV for measuring scavenging NOM scavenging measurement Proof of Concept experiments Incorporating some new ideas What s next?

4 Evolution of Scavenging Efficiencyof advanced oxidation processes (AOPs) is highly dependent on water quality, particularly background scavenging Background scavenging heavily influenced by NOM NOM is complex NOM is highly variable from location to location NOM is transient in nature Does relying on one rate constant to describe NOM reactivity really make sense? NOM reactivity controls design and control of AOP

5 Research Questions How do we define. OH radical scavenging in a water? Bulk parameter better than WQ estimates? Measurement issues (who measures and where?) Shipping issues? NOM may change character during shipment, especially if a residual oxidant in the sample (free or combined chlorine) Is it possible to measure OH radical scavenging onsite and quickly? Is it possible to measure OH radical reactivity with NOM rapidly, quickly, and cheaply?

6 R OH,UV Experimentally determined OH radical exposure per UV fluence. Defined for a given water matrix, initial H 2 O 2 Analogous to the R Ct parameter for ozone AOPs Measured by following the destruction of a probe compound para-chlorobenzoic Acid (pcba) Units of M s per mjcm -2

7 Derivation of R OH,UV Ozone R Ct (Elovitz and von Gunten, 1999) UV/H 2 O 2 R OH,UV (Rosenfeldt and Linden, 2007) ln [ M ] d dt ln [ M ] o [ M ] = [ M ] o [ M ] ( k [ O ][ M ] k [ OH ][ M ]) O, M 3 OH, M = k 3 + = k OH, M OH, M [ OH ] [ O ] R Ct 3 dt dt [ ] [ ] O3 dt O3 dt [ OH ] [ O ] 3 dt dt [ M ] d = dt ln k [ M ] o [ M ] ' ( k [ M ] + k [ OH ][ M ]) d OH, M = k OH, M [ OH ] [ OH ] ' D', M [ T = koh, M OH ] dt = t UV R OH,UV t dt dt 1 Fluence Ave Irr

8 What is the R OH,UV used for? Comparing efficiency of UV AOP 3.0E E E E-12 Water Quality comparisons 1.0E E E+00 Water 1, LP Water 1, MP [H 2 O 2 ] I (mm) Lamp type comparisons 3.0E E E E E E-13 Water 1 Water 2 Water 3 0.0E [H 2 O 2 ] i (mm)

9 Modeling with R OH,UV Use ROH,UV to measure background scavenging factor (Σk S,OH [S]) 1/ROH,UV (mj cm -2 M -1 s -1 ) 6.E+12 5.E+12 4.E+12 3.E+12 2.E+12 1.E+12 y = 6.72E+08x E+11 R 2 = 9.99E-01 k m b [ S] = k k [ pcba] S, OH i H2O2,OH pcba, OH 0.E /[H 2 O 2 ] i (M -1 ) Σk S,OH [S] x10-4 (s -1 ) Water Number measured with pcba probe calculated using water quality parameters Much lower scavenging predicted by R OH,UV method

10 Modeling with R OH,UV 7 6 [E2] i ~ 5µM Water 1 [E2] i ~ 3µM Water 2 k' x 10 3 (cm 2 mj -1 ) [H 2 O 2 ] i [ OH ] ss = λ k ( λ) Φ ( λ)[ H O ] a, H 2O2 H 2O2 OH k OH, S [ S] 2 2

11 Proof of Concept Experiments Project Objective Develop a rapid method for measuring background hydroxyl radical scavenging in a water Fast analysis (less than 30 minutes) Easy analysis Off-line process to avoid introduction of potentially harmful products Portable

12 Scavenging Measurement Methodology Measure oxidation of an organic dye, Methylene Blue (MB) by OH radical with LP UV + variable peroxide concentration Minimal direct UV photolysis No interaction with H 2 O 2 Define R OH,UV for system Rosenfeldt and Linden, 2007 Use R OH,UV to calculate background scavenging Water scavenging is defined for any AOP

13 Background Scavenging Measuring Apparatus Absorbance (cm -1 ) LP UV Lamp Time (s) Fiber optics Spectrometer Halogen Light Source ( nm) Measure rate of MB oxidation as a function of increased H 2 O 2 indicates amount of background scavenging present in the water.

14 Background Scavenging Measuring Apparatus

15 Background Scavenging Methodology Back out, or neglect, MB and H 2 O 2 contributions ( ) k S OH, S i Total [ ] ( ) k [ S] OH, S i Design

16 Proof of Concept Experiments Mirrored how the method would be used in the field Spiked 1µM MB into synthetic or natural water Divided into several initial H 2 O 2 Collect UV dose data UV 254, incident irradiance, etc. Expose to 300 mj/cm 2 and collect continuous MB decay data at 1 mw/cm 2 intervals Tackled variables of: TOC concentration Initial peroxide concentration Alkalinity effects (carbonate radical?)

17 Synthetic Waters Approach Mimic organic and inorganic scavenging in a controlled fashion Organic scavengers t-butyl Alcohol, Isopropyl Alcohol Inorganic scavengers Carbonate, bicarbonate Scavenging Species Second-Order Rate Constant with OH (M -1 s -1 ) DOC 2.5E+04 L mg -1 s -1 IPA 1.90E+09 tbuoh 7.30E+08 HCO 3 - CO 3 2- CO E E ± 1.5E+09

18 Synthetic Water Matrix Scavenging Species Equivalent Water Quality Concentration (mg/l) Concentration of Species (M) Equivalent Theoretical Scavenging (s -1 ) IPA 4 mg/l DOC 5.26E E+05 IPA 20 mg/l DOC 2.63E E+05 tbuoh 4 mg/l DOC 1.37E E+05 tbuoh 20 mg/l DOC 6.85E E+05 K 2 CO 3 20 mg/l Alk 2.00E E+04 4 mg/l DOC and 20 tbuoh and 1.37E-04 and mg/l Alk (80% DOC, K 2 CO E-04 20% Alk) 1.19E mg/l DOC and 50 tbuoh and mg/l Alk (10% DOC, K 2 CO 3 90% Alk) 1.37E-05 and 5.00E E+04

19 t-buohas an organic scavenging Spiked to 1.37 x 10-4 M Equivalent to 10 5 s -1 DOC scavenging (4 mg/l) Measured Background Scavenging = 1.03 x 10 5 s -1

20 Proof of Concept Summary Composition of Synthetic Water Theoretical Scavenging (s -1 ) Experimental Scavenging (s -1 ) Percent Difference (%) Low High Low H 2 O 2 High H 2 O 2 H 2 O 2 H 2 O 2 4 mg/l DOC as IPA 1.00E E E % 24.0% 20 mg/l DOC as IPA 5.00E E E % -4.2% 4 mg/l DOC as 1.00E E E % -9.0% tbuoh 20 mg/l DOC as tbuoh 5.00E E E % 1.2% 20 mg/l Alk as K 2 CO E E E % 657.3% 4 mg/l DOC as tbuoh and 20 mg/l 1.27E E E % 42.0% Alk as K 2 CO mg/l DOC as tbuoh and 50 mg/l 9.99E E+04 N/A -4.5% N/A Alk as K 2 CO 3

21 NOM Reactivity Measurement Competition kinetics for OH radical rate constants My student attempted to verify Paul Westerhoff s SuwaneeRiver FulvicAcid radical rate constant one Thursday morning last November in Amherst. Applied UV Fluence(mJ/cm2) ln{[mb]/[mb]o} mg/l H2O2 5 mg/l H2O2 (a) 5 mg/l H2O2 (b) 10 mg/l H2O2 15 mg/l H2O2 (a) 15 mg/l H2O2 (b) 20 mg/l H2O2-7

22 An interesting issue with the Hross method from Tanja Burgschwaiger in May, 2011 Huge impacts of initial concentration of Methylene Blue 5µm MB 1µm MB I think I have the answer to this interesting question!!!

23 Some new ideas Katsoyiannis, Canonica, von Gunten(20110 [ OH] Back to pcba(+ t-buoh), back to competition kinetics ss = k OH,DOM [ DOM] + k [ t BuOH] + k [ pcba] + k [ H O ] OH t BuOH α OH OH,pCBA OH,H 2 O k OH,DOM = A B k OH,t BuOH [DOM] A= Intercept, B = Slope k OH,pCBA From Rosenfeldt and Linden, 2004 [ pcba] + k OH,H [ H O ] 2O2 2 2 [ DOM]

24 Next project: starting this fall Collaborating with Krista Rule (Univ. Maryland, Washington Aqueduct, WSSC) Build statistical relationships between water quality and background scavenging Compare various calculation methodologies Katsoyiannis method may present a breakthrough Relate reactivity with NOM characterization Spectrometry/Fluorometry Portable Unit On-site measurement Examine changes in a day, week, month Examine effects of shipping samples Quenching of oxidants? Microbial effects? TOC changes in shipment, ph adjustment, temperature, etc.?

25 Portable Unit Difficult to lug a 60 pound UV box around 36 Everything smaller, and breaks down for shipping ~ Max Incident Intensity ~ 3.5 mw/cm 2 20 Detector Incident Intensity ~ mw/cm 2 Halogen Lamp

26 Summary NOM reactivity with OH radical controls AOP efficiency Variable reactivity impacts efficiency We have a method to measure background radical scavenging rapidly and accurately Basic methodology is sound Improvements possible with new competition kinetics method Portable unit key to the next steps On-site measurement Independent of shipping, quenching, etc.

27 Questions? Erik Rosenfeldt, PhD, PE Hazen and Sawyer