Photoelectrochemical Chemical Oxygen Demand Analysis in Drinking - PowerPoint PPT Presentation

Photoelectrochemical Chemical Oxygen Demand Analysis in Drinking Water Amina ¡Stoddart ¡ Civil and Resource Engineering Dalhousie University February ¡11, ¡2016 ¡

Introduction • Natural organic matter (NOM) is a critical target for drinking water treatment • NOM can be associated with – Taste, odour, colour issues – Coagulant, oxidant demand – DBP precursors – We have a number of tools for bulk NOM estimation: DOC, TOC, UV 254 , SUVA

Chemical Oxygen Demand (COD) Measurement in Drinking Water • Traditional NOM surrogates may not be suitable for assessing NOM removal in all cases – UV 254 , SUVA • Rely on aromaticity, which is not a chemical feature of many organic compounds, example sugars – Carbon (e.g., as TOC, DOC) • Does not quantify the reactivity of the organic

What is Chemical Oxygen Demand? TOC measures conversion to CO 2 + ¡O 2 ¡ ¡ à ¡CO 2 ¡+ ¡H 2 O ¡+ ¡NH 3 ¡

What is Chemical Oxygen Demand? TOC measures conversion to CO 2 + ¡O 2 ¡ ¡ à ¡CO 2 ¡+ ¡H 2 O ¡+ ¡NH 3 ¡ COD measures “demand” for oxygen

Why is COD not often used in Drinking Water? • The traditional method for COD determination is to oxidize with potassium dichromate under acidic conditions • Issues: – Sensitivity – Use of hazardous chemicals • Dichromate, mercury, surfuric acid – Analysis time • Hours

Photoelectrochemical COD (peCOD) Analysis • Safe for operator – No hazardous chemicals – Single reagent (electrolyte) • Takes 5-10 min – Can automate – Potential for online measurement • Low range – MDL = 0.5 mg/L (using modified procedure) • Uses green chemistry – No hazardous wastes

Working Principle: peCOD

Technical Approach 1. Conducted initial method validation with model organic compounds a. Compared peCOD of carboxylic acids, amino acids and reference compounds to the calculated theoretical oxygen demand (ThOD) b. Verified peCOD applicability in the drinking water NOM range of concern 2. Tested technology at various drinking water treatment plants 3. Monitored full-scale drinking water biofiltration

Method Validation: Comparison of peCOD and ThOD for Amino Acids 20.0 y = 1.14x - 1.18 Phenylalanine R ² = 0.98 y = 1.01x - 0.62 Tyrosine 15.0 R ² = 0.97 peCOD – mg/L Tryptophan y = 1.01x - 0.87 R ² = 0.99 10.0 5.0 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 ThOD – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Comparison of peCOD and ThOD for Amino Acids 20.0 y = 1.14x - 1.18 Phenylalanine R ² = 0.98 y = 1.01x - 0.62 Tyrosine 15.0 R ² = 0.97 peCOD – mg/L Tryptophan y = 1.01x - 0.87 R ² = 0.99 10.0 Slope value of unity would demonstrate that 5.0 peCOD was a complete predictor of ThOD 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 ThOD – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Comparison of peCOD and ThOD Carboxylic Acids 10.0 y = 1.47x - 0.13 Na-Oxalate R ² = 0.99 Na-Formate y = 0.96x - 0.58 R ² = 0.98 peCOD – mg/L Na-Acetate y = 0.79x - 1.34 R ² = 0.94 5.0 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 ThOD – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Comparison of peCOD and ThOD Carboxylic Acids 10.0 y = 1.47x - 0.13 Na-Oxalate R ² = 0.99 Na-Formate y = 0.96x - 0.58 R ² = 0.98 peCOD – mg/L Na-Acetate y = 0.79x - 1.34 R ² = 0.94 5.0 Slope value of unity would demonstrate that peCOD was a complete predictor of ThOD 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 ThOD – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Comparison of peCOD and TOC 20.0 • peCOD detectable at Phenylalanine y = 3.24x - 1.52 TOC concentrations R ² = 0.99 Tyrosine characteristic of raw and 15.0 y = 3.05x - 1.10 peCOD – mg/L treated water R ² = 0.96 Tryptophan – i.e., 1-5 mg C/L y = 3.11x - 1.30 10.0 R ² = 0.99 • peCOD:TOC ratios were predictable based on 5.0 stoichiometry of the oxidation reaction – i.e., oxygen to carbon 0.0 ratio 0.0 2.0 4.0 6.0 TOC – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Comparison of peCOD and TOC • peCOD detectable at 10.0 Na-Oxalate TOC concentrations y = 1.03x - 0.34 R ² = 0.99 characteristic of raw and Na-Formate y = 1.33x - 0.88 treated water peCOD – mg/L R ² = 0.98 – i.e., 1-5 mg C/L Na-Acetate y = 2.14x - 1.62 5.0 • peCOD:TOC ratios were R ² = 0.94 predictable based on stoichiometry of the oxidation reaction – i.e., oxygen to carbon 0.0 ratio 0.0 2.0 4.0 6.0 TOC – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Various Treatment Plants Direct Biofiltration Plant Conventional Filtration Plant 8.0 25.0 peCOD peCOD 7.0 TOC TOC Concentration – mg/L Concentration – mg/L 20.0 DOC DOC 6.0 5.0 15.0 4.0 10.0 3.0 2.0 5.0 1.0 0.0 0.0 Figures adapted from: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Various Treatment Plants Membrane Treatment Plant Conventional Filtration Plant 20.0 20.0 peCOD peCOD 18.0 18.0 TOC TOC Concentration – mg/L Concentration – mg/L 16.0 16.0 DOC DOC 14.0 14.0 12.0 12.0 10.0 10.0 8.0 8.0 6.0 6.0 4.0 4.0 2.0 2.0 0.0 0.0 Figures adapted from: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Various Treatment Plants in Nova Scotia - peCOD and TOC 25.0 Bennery Lake y = 2.69x - 0.49 Fletcher Lake R ² = 0.64 20.0 Lake Major Pockwock Lake peCOD – mg/L 15.0 10.0 5.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 TOC – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Various Treatment Plants in Nova Scotia - peCOD and DOC 25.0 Bennery Lake y = 3.04x Fletcher Lake R ² = 0.91 20.0 Lake Major peCOD – mg/L Pockwock Lake 15.0 10.0 5.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 DOC – mg/L Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Method Validation: Various Treatment Plants in Nova Scotia – peCOD and SUVA 25.0 Bennery Lake y = 4.27x - 2.26 Fletcher Lake R ² = 0.84 20.0 Lake Major Pockwock Lake peCOD – mg/L 15.0 10.0 5.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 SUVA – mg/L/cm 3 Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association , 106 (9).

Case Study: Biofiltration Monitoring

Biofiltration Monitoring : Background • Direct filtration drinking water treatment plant underwent conversion to biofiltration through removal of pre-chlorination • Conversion resulted in – Reduction in HAAs (~40-60%) and THMs (~20-60%) – Increase in bioactivity on the filter media • 40 ng ATP/cm 3 to 200-300 ng ATP/cm 3 • However, limited DOC removal across the filter occurred, making it difficult to assess treatment performance

Decrease in THM and HAA concentrations as a result of conversion 80 Filtration Biofiltration 60 THM— µg/L 40 20 0 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 60 Filtration Biofiltration 50 HAA— µg/L 40 30 20 10 0 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 Figure adapted from: Stoddart, A. K., & Gagnon, G. A. (2015). JAWWA.

Biofiltration Monitoring : Approach • Monitored NOM surrogates (TOC, DOC and peCOD) at 3 locations for a period of 9 months 1 2 3 Sample Points Figure adapted from: Stoddart, A. K., & Gagnon, G. A. (2015). JAWWA.

Effect of Flocculation • Limited removal of TOC Flocculation Raw Water to Biofilter Influent – TOC: 5 ± 4% 40% – Includes flocculated material 35% • Similar removal of DOC 30% and peCOD Percent Removal 25% – DOC: 31 ± 4% 20% • Does not measure flocculated material 15% (0.45 µm filtration as 10% sample preparation) – peCOD: 32 ± 3% 5% • Assumed to measure only 0% soluble portion TOC DOC peCOD Error bars represent 95% CI