role in treatment of emerging contaminants in north carolina uv & ozone mediated advanced...
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UCMR 3 & 1,4-DIOXANE IN NC WATERS 3TRANSCRIPT
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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