AWRA Meeting Philadelphia PA March 21 2013 Adrienne Donaghue Brian P Chaplin Villanova University Department of Civil amp Environmental Engineering Electrochemical Oxidation for Water Treatment and the ID: 772948
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AWRA Meeting Philadelphia, PAMarch 21, 2013Adrienne DonaghueBrian P. ChaplinVillanova UniversityDepartment of Civil & Environmental Engineering Electrochemical Oxidation for Water Treatment and the Limitation of Hazardous Byproducts
Introduction Electrochemical oxidation has become promising for treatment of recalcitrant and biorefractory waste streamsAdvantages:Easy installation and operationCost effectiveEnvironmentally friendly 2
Oxineo ®Environmental Applications Electrochemical Oxidation Pilot plant for landfill leachate in Cantabria, Spain. 3
Electrochemical Reactions Power Supply + _ Anode Cathode e - H 2 O OH + H + + e - OH OH OH OH OH OH OH 4
Electrochemical Oxidation Destruction of pollutants occurs through 2 mechanisms: 1. Direct electron transfer (DET) 2. Indirect oxidation via hydroxyl radicals (OH●) * Electrochemical material plays important role in the effectiveness of oxidation! 5 Indirect electrochemical oxidation Anode Adsorbed • OH current • OH Free • OH R RO R or RO CO₂ + H₂O Oxygen Evolution Direct electrochemical oxidation e- Zhu et. al, 2008.
Boron Doped Diamond Electrode Boron-doped diamond (BDD) film grown on p-silicon substrate using CVD (Advanced Diamond Technologies).Boron doping @ ppm levels provides electrical conductivity.Inert surface and low adsorption propertiesRemarkable corrosion satiabilityProduces large amount of OH● (weakly adsorbed) Emerging AOP technology . Can oxidize perfluorinated compounds Note! These compounds can not be degraded by other AOP technologies 6
Farrell et al. (2008) Perfluorooctane Sulfunate (PFOS) (C ₈ F ₁₇SO₃⁻) 7
By-product/Perchlorate (ClO 4-) FormationIs a multi-step processHazardous to human healthEPA set an advisory limit of 15 ppb for drinking water sourcesCA and MA drinking water limits of 2 and 6 ppb Cl - OCl - ClO₂ - ClO₃ - ClO₄ - 8 Rate-limiting step
9 By-product/ClO4- Formation Cont. Azizi et. al, 2011 2 step process: Cl - OCl - ClO₂ - ClO₃ - ClO₄ - Rate-limiting step Reaction Zone Anode ClO ₃⁻ OH ● e - ClO 3 ● ClO 4 - 1. 2.
Research Objectives Understand how the reactivity of certain organics effect perchlorate formation at the anode surfaceUse “model” p-substituted phenols to determine the importance of each step in the two step process of perchlorate formation. Model organic behavior with in the diffuse and reaction zones to understand mechanisms of inhibition of ClO4- at the anode surface 10 1) 2)
Experimental Setup 11Batch ReactorRotating Disk Electrode (RDE) Organic compounds p -nitrophenol (p-NP) p -methoxyphenol (p-MP) p -benzoquinone (p-BQ) Oxalic acid (OA) S olutions were tested at: Kinetically Control: 1.0 mA/cm ² Mass-transfer Control: 2.4 mA/cm ², 10.0 mA /cm²
12 Results: ClO₄⁻ Formation OH• Rate Constant * Log Kow (L mol⁻¹ s⁻¹) p -nitrophenol (p-NP) 3.8x10⁹ 1.91 p -benzoquinone (p-BQ) 6.6x10⁹ 0.2 p -methoxyphenol (p-MP) 2.6x10¹⁰ 1.34 oxalic acid (OA) 1.4x10⁶ -0.81 * Buxton et al. 1988 Initial Organic Concentration = 250 μ M
13 Results: Organic Reactivity C x/L Anode Diffuse Layer COMSOL ® Anode Surface OH ● ClO ₃● R B Diffusion Zone Reaction Zone 2 μ m 5 μ m
Results: ClO ₄⁻ Formation14
Conclusions: 15Limiting ClO₄- formationRate limiting step is a two step processReactions occur right at surface Organic reactivity is important For Low Current Densities: Scavenging occurs on surface For High Current Density: Location becomes important Anode ClO ₃⁻ OH ● e - ClO 3 ● ClO 4 - Step 1 Step 2
Conclusion Cont. Operating under MT conditions is the most effective means to limit ClO4- formation.In addition, operating at these conditions is cost effective.EC is viable technology for refractory organic pollutants but in order for it to be integrated into environmental applications, ClO4- must be inhibited below advisory levels. 16
Acknowledgements This research was funded by Advanced Diamond Technologies (ADT) in Romeoville, IL via NSF SBIR Phase II grant.Special thanks to my advisor Dr. Brian P. Chaplin 17
Questions?
Results: LSV of p-substituted phenols 19 Blank Blank Blank 1 mM 5 mM 10 mM 0.75 mM 1.0 mM 0.25 mM 0.50 mM
20 Measured Rates vs. Mass Transfer
OH ● OH ● OH ● OH ● R R R ClO 3 ● ClO 3 ● ClO 3 ● ClO ₄⁻ ClO ₄⁻ Anode
Reaction Zone Anode ClO ₃⁻ OH ● e - ClO 3 ● ClO 4 -