Photoelectrochemical Chemical Oxygen Demand Analysis in Drinking - - PowerPoint PPT Presentation

Civil and Resource Engineering Dalhousie University

Photoelectrochemical Chemical Oxygen Demand Analysis in Drinking Water

Amina ¡Stoddart ¡

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, UV254, SUVA

Chemical Oxygen Demand (COD) Measurement in Drinking Water

• Traditional NOM surrogates may not be

suitable for assessing NOM removal in all cases

– UV254, SUVA

• Rely on aromaticity, which is not a chemical feature
• f many organic compounds, example sugars

– Carbon (e.g., as TOC, DOC)

• Does not quantify the reactivity of the organic

What is Chemical Oxygen Demand?

+ ¡O2 ¡ ¡à ¡CO2 ¡+ ¡H2O ¡+ ¡NH3 ¡ TOC measures conversion to CO2

What is Chemical Oxygen Demand?

+ ¡O2 ¡ ¡à ¡CO2 ¡+ ¡H2O ¡+ ¡NH3 ¡ COD measures “demand” for oxygen TOC measures conversion to CO2

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

• f 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

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 1.14x - 1.18 R² = 0.98 y = 1.01x - 0.62 R² = 0.97 y = 1.01x - 0.87 R² = 0.99 0.0 5.0 10.0 15.0 20.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 peCOD – mg/L ThOD – mg/L Phenylalanine Tyrosine Tryptophan

Method Validation: Comparison of peCOD and ThOD for Amino Acids

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 1.14x - 1.18 R² = 0.98 y = 1.01x - 0.62 R² = 0.97 y = 1.01x - 0.87 R² = 0.99 0.0 5.0 10.0 15.0 20.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 peCOD – mg/L ThOD – mg/L Phenylalanine Tyrosine Tryptophan

Slope value of unity would demonstrate that peCOD was a complete predictor of ThOD

Method Validation: Comparison of peCOD and ThOD Carboxylic Acids

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 1.47x - 0.13 R² = 0.99 y = 0.96x - 0.58 R² = 0.98 y = 0.79x - 1.34 R² = 0.94 0.0 5.0 10.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 peCOD – mg/L ThOD – mg/L Na-Oxalate Na-Formate Na-Acetate

Method Validation: Comparison of peCOD and ThOD Carboxylic Acids

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 1.47x - 0.13 R² = 0.99 y = 0.96x - 0.58 R² = 0.98 y = 0.79x - 1.34 R² = 0.94 0.0 5.0 10.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 peCOD – mg/L ThOD – mg/L Na-Oxalate Na-Formate Na-Acetate

Slope value of unity would demonstrate that peCOD was a complete predictor of ThOD

Method Validation: Comparison of peCOD and TOC

• peCOD detectable at

TOC concentrations characteristic of raw and treated water

– i.e., 1-5 mg C/L

• peCOD:TOC ratios were

predictable based on stoichiometry of the

• xidation reaction

– i.e., oxygen to carbon ratio

y = 3.24x - 1.52 R² = 0.99 y = 3.05x - 1.10 R² = 0.96 y = 3.11x - 1.30 R² = 0.99 0.0 5.0 10.0 15.0 20.0 0.0 2.0 4.0 6.0 peCOD – mg/L TOC – mg/L Phenylalanine Tyrosine Tryptophan

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

TOC concentrations characteristic of raw and treated water

– i.e., 1-5 mg C/L

• peCOD:TOC ratios were

predictable based on stoichiometry of the

• xidation reaction

– i.e., oxygen to carbon ratio

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 1.03x - 0.34 R² = 0.99 y = 1.33x - 0.88 R² = 0.98 y = 2.14x - 1.62 R² = 0.94 0.0 5.0 10.0 0.0 2.0 4.0 6.0 peCOD – mg/L TOC – mg/L Na-Oxalate Na-Formate Na-Acetate

Method Validation: Various Treatment Plants

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).

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Concentration – mg/L peCOD TOC DOC 0.0 5.0 10.0 15.0 20.0 25.0 Concentration – mg/L peCOD TOC DOC

Direct Biofiltration Plant Conventional Filtration Plant

Method Validation: Various Treatment Plants

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).

Membrane Treatment Plant Conventional Filtration Plant

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Concentration – mg/L peCOD TOC DOC 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Concentration – mg/L peCOD TOC DOC

Method Validation: Various Treatment Plants in Nova Scotia - peCOD and TOC

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 2.69x - 0.49 R² = 0.64 0.0 5.0 10.0 15.0 20.0 25.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 peCOD – mg/L TOC – mg/L Bennery Lake Fletcher Lake Lake Major Pockwock Lake

Method Validation: Various Treatment Plants in Nova Scotia - peCOD and DOC

y = 3.04x R² = 0.91 0.0 5.0 10.0 15.0 20.0 25.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 peCOD – mg/L DOC – mg/L Bennery Lake Fletcher Lake Lake Major Pockwock Lake

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

Figure: Stoddart, A. K., & Gagnon, G. A. (2014). Application of photoelectrochemical chemical oxygen demand to drinking water. Journal: American Water Works Association, 106(9).

y = 4.27x - 2.26 R² = 0.84 0.0 5.0 10.0 15.0 20.0 25.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 peCOD – mg/L SUVA – mg/L/cm3 Bennery Lake Fletcher Lake Lake Major Pockwock Lake

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/cm3 to 200-300 ng ATP/cm3
• However, limited DOC removal across the filter
• ccurred, making it difficult to assess treatment

performance

Decrease in THM and HAA concentrations as a result of conversion

Figure adapted from: Stoddart, A. K., & Gagnon, G. A. (2015). JAWWA.

20 40 60 80 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 THM—µg/L Filtration Biofiltration 10 20 30 40 50 60 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 HAA—µg/L Filtration Biofiltration

Biofiltration Monitoring : Approach

• Monitored NOM surrogates (TOC, DOC and

peCOD) at 3 locations for a period of 9 months

Figure adapted from: Stoddart, A. K., & Gagnon, G. A. (2015). JAWWA.

Sample Points 1 2 3

Effect of Flocculation

• Limited removal of TOC

– TOC: 5 ± 4% – Includes flocculated material

• Similar removal of DOC

and peCOD

– DOC: 31 ± 4%

• Does not measure

flocculated material (0.45 µm filtration as sample preparation)

– peCOD: 32 ± 3%

• Assumed to measure only

soluble portion

0% 5% 10% 15% 20% 25% 30% 35% 40% TOC DOC peCOD Percent Removal

Flocculation Raw Water to Biofilter Influent

Error bars represent 95% CI

Effect of Biofiltration

• Greatest average

removal of TOC

– TOC: 29 ± 4% – Flocculated material filtered out

• Limited average

removal of DOC

– DOC: 2 ± 1%

• More peCOD removal

– peCOD: 19 ± 5%

0% 5% 10% 15% 20% 25% 30% 35% TOC DOC peCOD Percent Removal

Biofiltration Biofilter Influent to Biofilter Effluent

Error bars represent 95% CI

Effect of Flocculation and Biofiltration

NOM ¡Surrogate ¡ Raw ¡ ¡ Water ¡ Flocculated ¡ Water ¡ Biofiltered ¡ ¡Water ¡ TOC—mg/L ¡ 3.16 ¡± ¡0.13 ¡ 3.00 ¡± ¡0.16 ¡ 2.06 ¡± ¡0.07 ¡ DOC—mg/L ¡ 3.04 ¡± ¡0.34 ¡ 2.07 ¡± ¡0.06 ¡ 2.09 ¡± ¡0.12 ¡ peCOD—mg/L ¡ 8.51 ¡± ¡0.55 ¡ 5.90 ¡± ¡0.46 ¡ 4.64 ¡± ¡0.42 ¡

Effect of Flocculation and Biofiltration

NOM ¡Surrogate ¡ Raw ¡ ¡ Water ¡ Flocculated ¡ Water ¡ Removal ¡ Biofiltered ¡ ¡Water ¡ Removal ¡ TOC—mg/L ¡ 3.16 ¡± ¡0.13 ¡ 3.00 ¡± ¡0.16 ¡ 0.16 ¡ 2.06 ¡± ¡0.07 ¡ 0.94 ¡ DOC—mg/L ¡ 3.04 ¡± ¡0.34 ¡ 2.07 ¡± ¡0.06 ¡ 0.97 ¡ 2.09 ¡± ¡0.12 ¡

• ­‑0.05 ¡

peCOD—mg/L ¡ 8.51 ¡± ¡0.55 ¡ 5.90 ¡± ¡0.46 ¡ 2.61 ¡ 4.64 ¡± ¡0.42 ¡ 1.26 ¡

Treatment Train: Combined Effect of Flocculation and Biofiltration

0% 10% 20% 30% 40% 50% 60% TOC DOC peCOD Percent Removal Flocculation Biofiltration

Error bars represent 95% CI

Treatment Train: Combined Effect of Flocculation and Biofiltration

SUVA Expected DOC Removal Using Alum ¡

>4 >50% 2-4 25-50% <2 <25%

Source water SUVA: 3.4 ± 0.1 Expected DOC removal with alum1: 25-50%

• Table. Adapted from Edzwald and Tobiason, 1999; 1Edzwald and Tobiason, 1999

Treatment Train: Combined Effect of Flocculation and Biofiltration

0% 10% 20% 30% 40% 50% 60% TOC DOC peCOD Percent Removal Flocculation Biofiltration

Error bars represent 95% CI

Physical/chemical Removal: ~35%

Treatment Train: Combined Effect of Flocculation and Biofiltration

0% 10% 20% 30% 40% 50% 60% TOC DOC peCOD Percent Removal Flocculation Biofiltration

Error bars represent 95% CI

Physical/chemical Removal: ~35% Bio-oxidative Removal (?): ~15%

Decrease in THM and HAA concentrations as a result of conversion

Figure: Stoddart, A. K., & Gagnon, G. A. (2015). JAWWA.

20 40 60 80 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 THM—µg/L Filtration Biofiltration 10 20 30 40 50 60 26-Feb-11 14-Sep-11 1-Apr-12 18-Oct-12 6-May-13 22-Nov-13 10-Jun-14 27-Dec-14 HAA—µg/L Filtration Biofiltration

Does removal of these compounds translate to improved DBP control?

Conclusions

• peCOD can measure NOM rapidly, at low

concentrations and without the use of hazardous chemicals

• peCOD is an appropriate bulk NOM

parameter

• The use of peCOD to monitor biofiltration

may provide additional information on NOM removal and subsequent biofilter performance to compliment other NOM surrogates