ROLE IN TREATMENT OF EMERGING CONTAMINANTS IN NORTH CAROLINAUV & OZONE MEDIATED ADVANCED OXIDATION

Paul Hargette & Bryan TownsendB&V Water Technology Group

NC AWWA-WEA 95TH ANNUAL CONFERENCE

AGENDAUCMR 3 & 1,4-Dioxane in NC Waters

1,4-Dioxane Characteristics

Ozone & UV Advanced Oxidation

Conclusions

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UCMR 3 & 1,4-DIOXANE IN NC WATERS

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• Monitoring of contaminants suspected to be present in drinking water • Not currently regulated• May warrant future regulation

under the SDWA

• 30 Contaminants• 28 chemicals and 2 viruses

• 12 month monitoring period from Jan 2013 – Dec 2015• Approximately 3,500 participating systems nation wide

3RD UNREGULATED CONTAMINANT MONITORING RULE (UCMR 3)

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• Assessment Monitoring (List 1 Contaminants)• 7 Volatile organic compounds• 1 Synthetic organic compound (1,4-Dioxane)• 6 Metals• 1 Oxyhalide anion• 6 Perfluorinated compounds

• Screening Survey (List 2 Contaminants)• 7 Hormones

• Pre-Screen Testing (List 3 Contaminants)• 2 Viruses

UCMR 3 CONTAMINANTS

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1,4-DIOXANE IN NORTH CAROLINA

6Source: UCMR 3 Database (through June 2015)

Participating NC PWSs, Total & with 1,4-Dioxane

Source Waters for PWSs with 1,4-Dioxane

Source: UCMR 3 Database (through June 2015)

DISTRIBUTION OF 1,4-DIOXANE DATA

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MRL = 0.07 μg/l

1,4-DIOXANE CHARACTERISTICS

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• Industrial solvent stabilizer (e.g. TCA)• Commercial products

• Paint strippers, dyes, greases, varnishes, waxes, antifreeze and aircraft deicing fluids

• Consumer products• Deodorants, shampoos & cosmetics

• Manufacturing • Byproduct of polyethylene terephthalate (PET) plastic• Purifying agent in the manufacturing of pharmaceuticals

• 1,4-Dioxane residues may be present in food• Manufactured food additives, food packaging materials or food

crops treated with pesticides containing 1,4-Dioxane

1,4-DIOXANE

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• Potential sources• Wastewater discharge• Unintended spills, leaks• Historical solvent disposal practices

• Group B2 (probable human) carcinogen• Acute (short term) exposure in humans (via inhalation): vertigo,

drowsiness, headache, anorexia and irritation of the eyes, nose, throat and lungs

• Chronic (long term) exposure in test animals (via drinking water): damage to liver, kidneys and gall bladder

• EPA 10-6 cancer risk level of 0.35 μg/l

SOURCES & HEALTH IMPACTS

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DRINKING WATER GUIDELINES

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State Guideline [1,4-D] (μg/l)CA Notification level 1CO Drinking water standard 3.2CT Action level 3ME Max exposure guideline 4MA Guideline 0.3NH Proposed risk-based remediation value 3NY Drinking water standard 50SC Drinking water health advisory 70

Source: Water Research Foundation, 2014

• International guidelines vary between 0.1 and 50 μg/l

• Dissolves readily into water• Highly mobile,• Recalcitrant to microbial degradation• Very stable, not readily volatile in water

• Majority of treatment processes ineffective• Conventional treatment• Air stripping • Activated carbon• Reverse osmosis• Ozone • UV (not susceptible to direct photolysis)

• Advanced oxidation is effective

TREATMENT OPTIONS

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OZONE & UV ADVANCED OXIDATION

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• Generation & application of highly reactive free radicals• Hydroxyl radical (OH◦) – most common

• Reacts rapidly and unselectively• Most potent oxidant used in water treatment

• Destruction of a variety of recalcitrant contaminants• Attractive option vs. other conventional oxidants• Treatment of drinking water, water reuse, remediation

ADVANCED OXIDATION

Cl2 (1.36 V)

ClO2 (1.50 V)

O3 (2.07 V)

OH◦ (2.80 V)

• Commonly applied AOPs• Ozone (O3)/Hydrogen Peroxide (H2O2)• UV/H2O2

• Emerging AOPs• UV/Chlorine (Cl2) – only a few full-scale facilities in operation• UV/Electrode – piloting experience

• Other AOPs (not commonly applied)• O3/UV – very $$ (UV/H2O2 or O3/H2O2 typ. more economical)• UV/TiO2

• FeII/H2O2 (Fenton’s reagent)

ADVANCED OXIDATION PROCESSES

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• Taste & Odor• 2-Methylisoborneol (MIB), Geosmin

• Algal Toxins• Cylindrospermopsin, Anatoxin-a, Microcystin-LR, Saxitoxin

• Emerging Contaminants• Volatile organic compounds (e.g. TCE, PCE)• Semivolatile organic chemicals (e.g. NDMA)• Synthetic organic chemicals (e.g. 1,4-Dioxane)• Pesticides (e.g Metaldehyde)• Endocrine disrupting compounds (EDC’s)• Pharmaceuticals

EFFECTIVE TREATMENT FOR A VARIETY OF COMPOUNDS

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• OH◦ scavengers - Water constituents that compete for OH◦ with target contaminant and are typ. present in higher concentrations• Carbonate (CO3

2-) and bicarbonate (HCO3-): AOP is more effective

at lower alkalinities• Natural organic matter (NOM): AOP best applied downstream of

solid-liquid separation following reduction of organic load

• Byproducts • Complete oxidation of contaminants to carbon dioxide and water

is possible (in theory), but not economical• Breaking down complex organics to less innocuous and/or more

biodegradable compounds• Increase in assailable organic carbon (AOC) • Other byproducts need to be considered

WATER QUALITY CONSIDERATIONS COMMON TO ALL AOPS

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• OH◦ is produced via O3 natural decomposition • Self propagating chain reaction• Dual oxidation via O3 and OH◦ (limited)

• O3/H2O2 AOP (AKA “Peroxone”)• Reaction btw O3 and NOM is preferred and

instantaneous (i.e. O3 demand)• H2O2 initiates decomposition cycle of remaining

O3→ OH◦

• Potential benefits (vs. UV AOPs)• Reduced energy and [H2O2] requirements• Reduced maintenance (vs. lamp replacements)

• Process challenges/considerations• Byproduct formation (bromate)

O3/H2O2 ADVANCED OXIDATION

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• pH: neutral to basic (typ. 6.5 – 8)• O3 demand of water• OH◦ scavenging demand• Ratio of H2O2:O3 is key

• H2O2 is also an OH◦ scavenger • Typ. goal is to optimize ratio to minimize both

O3 and H2O2 residual

• Bromate formation• Excess H2O2 may be used in high bromide

waters to limit reaction with O3 and bromate formation (up to 90% H2O2 residual)

• Treatment of H2O2 residual (if present)• Chlorine or activated carbon

O3/H2O2 TREATMENT R

CONSIDERATIONS

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• Injection of oxidant upstream of UV• H2O2 or Cl2

• UV exposure results in formation of OH◦ and advance oxidation

• Potential benefits• Reduced footprint and typ. lower

capital as compared to O3 (T&O) and O3 AOP (recalcitrant contaminants)

• No bromate formation concerns (for H2O2)• Not impacted by typical water temperatures • Some contaminants (NDMA) are susceptible to direct photolysis

• Increased treatment efficiency via dual destruction pathways (direct photolysis and advanced oxidation)

UV ADVANCED OXIDATION

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• High power consumption / operating costs• Require significantly more energy than UV

disinfection systems (magnitude or more than required for disinfection)• UV doses btw 500 to 4,000 mJ/cm2 (vs. ≤

40 mJ/cm2 typ. used in disinfection)• Duration of treatment is important for

economics • Seasonal T&O treatment – operated for

disinfection majority of year

• Treatment of oxidant residual (for UV/H2O2)• Costs are highly variable and site specific

(capital and O&M)• Reactor-specific dose delivery efficiency• Site-specific water quality

UV AOP CHALLENGES

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• Scavenging demand• Ratio of UV dose : oxidant dose

• Similar levels of treatment can be obtained by decreasing the oxidant dose with an increasing UV dose (or vice versa)

• Optimize balance between:• Oxidant costs: chemical supply, storage & dosing equipment• UV costs: equipment, operating power, maintenance

• Byproducts• Nitrate formation for MP systems (wavelengths < 240 nm)• Chlorinated by-products & bromate formation for UV/Cl2 AOP

• Treatment of oxidant residual • Required for UV/H2O2, not typ. required for UV/Cl2

UV AOP TREATMENT CONSIDERATIONS

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• Full-scale systems not validated• At least not at the UV doses used

for advanced oxidation• Validation data may be used to

confirm CFDi model accuracy

• UV manufacturers use a variety of techniques/approaches• Testing (pilots and/or bench-scale)

• Determine relationship btw UV dose, oxidant dose & contaminant removal

• Water quality analyses: UVT, UVA scan, scavenging demand• Results of UV AOP pilots not scalable to full-scale

• CFDi modeling• Determine UV system design & power requirements to

achieve required treatment based on test results

UV AOP SIZING

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• Photochemical cleavage of H2O2 → OH◦• Process limitations / considerations

• Poor absorbance of UV by H2O2

• High H2O2 dose requirements (2 to 15 mg/l)

• High UV doses (i.e. increased energy)• Inefficient reaction

• Only 5 – 10% of H2O2 consumed in reaction• Large H2O2 residual downstream of UV that

must be quenched (Cl2, GAC, BAC)

• Not impacted by typical water pH• Byproduct potential concerns limited to

nitrate formation with MP systems

UV/H2O2 AOP

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• Production of OH◦ & chlorine radicals (Cl◦)• Advantages over UV/H2O2 AOP

• HOCl has higher UV absorbance and lower scavenging rate than H2O2

• Potential for increased OH◦ production efficiency, reduced oxidant dose & smaller UV system

• Small residual: 75-99% of Cl2 consumed• Cl2 disinfection = no quenching required

• Process Limitations / Considerations• Chlorine speciation is key: OCl- scavenging rate is 104 greater

than HOCl = max pH of 6-6.5• Cl2 dose limited (≤ 5 mg/l): Pitting of stainless steel• Cl◦ byproducts: limited data (TTHMs, HAA, chlorite, chlorate?)

UV/Cl2 AOP

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• Developed by ETS• Electrode replaces oxidation injection

• Anode: TDS → OCl- + HOCl, UV photolysis of HOCl → OH◦ + Cl◦

• Cathode: H2O → H+ + OH-, UV photolysis of OH- OH◦

• Advantages• No oxidant injection or residual quenching• Minimal power for electrode (20 W)

• Process Limitations/Considerations• Anode: TDS ≥ 350 mg/l, pH ≤ 6.5, Cl◦ byproduct potential• Cathode: Hydrogen off-gas• Limited experience/applications

UV/ELECTRODE AOP

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CONCLUSIONS

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• 1,4-Dioxane has been reported by over 28% of N. Carolina PWSs participating in the UCMR 3• Concentrations ranging up to 190 times the MRL of 0.07 μg/l

• Conventional treatment, activated carbon, air stripping, RO as well as O3 and UV alone are not effective for 1,4-Dioxane

• O3 and UV AOPs provide effective treatment for 1,4-Dioxane as well as a variety of other recalcitrant contaminants• Taste & Odor• Algal Toxins• VOCs, NDMA• Pesticides, EDCs and pharmaceuticals

CONCLUSIONS

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