Jens Muff, AAU Esbjerg. Examples of an Electrochemical Advanced ...

Examples of an Electrochemical
Advanced Oxidation Process (EAOP) for
degradation of pesticides, PAHs and other
recalcitrant organics in water
Jens Muff
Section of Chemical Engineering
Department of Biotechnology, Chemistry and Environmental Engineering
Aalborg University
1

Agenda
• EAOP in comparison to other AOPs
• Principle of electrochemical oxidation (EO)
• Examples of applications:
• Case study 1: Høfde 42 (Pesticides)
• Case study 2: Sediment dredging (PAHs)
• Case study 3: Kærgaard (Pharmaceuticals, solvents)
• Concluding remarks and perspectives
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Advanced Oxidation Processes (AOPs)
“Aqueous phase oxidation methods intermediated of highly reactive species
such as (primarily but not exclusively) hydroxyl radicals in the mechanisms
leading to destruction of the target pollutants” 1
AOPs
pollutant
OH CO H O
2 2
inorganic compounds
Electrochemical oxidation!
1
Comninellis et al (2008) J Chem Technol Biotechnol 83:769-776 ; 2 Poyatos et al. (2010) Water Air Soil Pollut, 205, p. 187-204
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What can they be used for
… matrices that are too diluted to incinerate or too
concentrated or/and toxic to treat biologically
Areas:
• Industrial effluent treatment:
– Distillery, agrochemical, kraft-bleaching, pulp and paper, textile dye-house, oilfield
and metal-plating
• Hazardous effluent treatment:
– Hospitals and slaughterhouses
• Removal of pathogens and persistent, endocrine disrupting
pharmaceutical residues from municipal WWTP effluents
• Removal of organic micro-pollutants such as pesticides from water
Aim: Degradation of recalcitrant non-biocompatible organics:
• Improvement of the BOD/COD ratio (partial or full mineralization) in pre-treatment
• Polishing step (tertiary treatment)
• Inactivation or killing of microorganisms (disinfection)
Source: Comninellis et al. (2008) J Chem Technol Biotechnol, 83, 769-776
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EAOP versus other AOPs
Why electrochemical oxidation:
Challenges:
• Environmental compatible technique: use of a
“clean” reagent (the electron), no addition of
excess chemicals, only electricity is required
• Power consumption: Currently, when
optimized for waste water treatment not
below 30 kWh/kg COD removed
• Control of reaction rate: Through control of
applied current. the process can be turned on
and off
• Versatile: non-selective towards a wide range
of organic pollutants
• Less independent of temperature: Compared
to chemical oxidation
• Capacity: Expensive with large flow rates
• Corrosion/Damage to electrodes: Long term
stability and fouling cause challenges
• Risk of byproduct formation: Byproducts are
formed, and need to be taken into concern
• Amenability to automation: Simple to operate
and automate
Walsh F.C. (2001) Pure an applied chemistry, 73, 12, 1819-1837
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Reaction mechanisms in EO
Active oxygen formation
MO + H +
(chemi-sorption)
M( OH) + H +
(physi-sorption)
e -
e -
Direct oxidation
R
R
H 2 O
e -
EOTR*
R
-Pt-Pt-Pt-Pt-Ir-Pt-Pt-Pt-Pt-
ROH / RO
CO 2 + H 2 O
* EOTR = Electrochemical oxygen transfer reaction (EOTR)
Comninellis, C. (1994) Electrochimica Acta, 39, 1857-1862 ; Bonfatti, F. et al. (2000) Journal of the Electrochemical Society, 147 (2), 592-596
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Reaction mechanisms in EO
Active oxygen formation
MO + H +
(chemi-sorption)
M( OH) + H +
(physi-sorption)
e -
e -
Direct oxidation
R
R
H 2 O
e -
EOTR*
R
-Pt-Pt-Pt-Pt-Ir-Pt-Pt-Pt-Pt-
ROH / RO
CO 2 + H 2 O
Cl - + M( OH)
e -
M(HOCl) ads
R
CO 2 + H 2 O+ Cl -
e -
Indirect mediated oxidation
2Cl -
Cl -
Cl 2 + H 2 O → HOCl + H + + Cl -
CO 2 + H 2 O
R
* EOTR = Electrochemical oxygen transfer reaction (EOTR)
Comninellis, C. (1994) Electrochimica Acta, 39, 1857-1862 ; Bonfatti, F. et al. (2000) Journal of the Electrochemical Society, 147 (2), 592-596
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Side reactions and anode materials
Primary cathode reaction:
Unwanted side reaction (loss of efficiency):
Direct oxidation power:
2H2O 4e H
2
2OH
2H2O O2
4H 4e
-
-
MO M O
1
2
M ( OH ) M O H e
2
1
2
2
Electrode
material
Oxidation potential
/ V
Overpotential of O 2
evolution / V
Adsorption
enthalpy of
MO x ( . OH)
Oxidation power of
the anode
“Active”
“Non-active”
RuO 2 -TiO 2 1.4-1.7 0.18
IrO 2 -Ta 2 O 5 1.5-1.8 0.25
Ti/Pt 1.7-1.9 0.3
Ti/PbO 2 1.8-2.0 0.5
Ti/SnO 2 -Sb 2 O 5 1.9-2.2 0.7
p-Si/BDD 2.2-2.6 1.3
Chemisorption of
OH radical
Physisorption of
OH radical
Si/BDD: Full mineralization
Ti/Pt: Partial mineralization
Kapalka et al. (2008) Journal of Applied Electrochemistry, 38, 7-16
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Case study 1: Høfde 42 (Pesticides)
1953–1962:
Deposition of primarily pesticides in the sand dunes
near Høfde 42
1981:
Excavation of 1200 tons of chemicals, 120 tons were
left behind.
2006:
Installation of 600 m of sheet piles => immobilization
of the pollution (ca. 98%)
2007–2008:
Pilot scale study: Alkaline hydrolysis and biological
degradation
2010-13:
Alkaline hydrolysis demonstration project with tests of
different enhancement methods (NorthPestClean)
Parathion
Malathion
Source: Google Earth
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Case study 1: Høfde 42 (Pesticides)
COD
Overall oxidation
Specific compounds
Parent pesticides
Degradation products
J. Muff, et al. (2009), Electrochim. Acta, 54, 2062-2068
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Case study 1: Høfde 42 (Pesticides)
• Efficient for degradation of the target pollutants
• Non-polar byproducts not present
– Substitute granulated active carbon adsorption
– Need to check for other byproducts
• Indirect treatment possible
– Possible in-situ soil treatment (ISCO)
– Re-infiltration of EC oxidant
Intermixing approach (1:1)
EC
J. Muff, et al. (2009), Electrochim. Acta, 54, 2062-2068
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Case study 2: Sediment dredging (PAHs)
Dredging of sediment from harbours to maintain sail channels.
Chemicals of concern:
• Polycyclic aromatic hydrocarbons (PAHs)
• Tri-butyl-tin (TBT)
PAHs:
Sources
• Incomplete combustion of carbon sources (fossil
fuel, diesel, cigarettes, wood stoves)
Human health effects
• Highly toxic, carcinogenic, mutagenic
Threshold value (drinking water)
• 0.010 – 0.005 µg L -1
Characteristics
• Multiple ring structures, lipophilic and hence low
water solubility, persistent, recalcitrant, and nonreactive
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Case study 2: Sediment dredging (PAHs)
Process water from harbour
sediment dredging
Direct EO treatment
Treatment cost:
• 13.2 kWh m -3
Intermixing approach
Treatment cost:
• 19 kWh m -3
Naphthalene, pyrene and fluoranthene
J. Muff and E. Søgaard (2010) Water Science and Technology, 61.8, pp. 2043-2051
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Case study 3: Kærgaard Plantation
(Pharmaceuticals)
Kærgaard Plantation: Chemical waste and waste water
from Grindstedværket
Contaminants: sulfonamides, barbiturates, aniline, pyridine,
chlorinated solvents, mercury, cyanide, BTEX amo.
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Case study 3: Kærgaard Plantation
(Pharmaceuticals)
Groundwater samples from hot spot in pit 1 (13.6- 14.3 m bgs). Prior to use in the
experiment, the water was bubbled with atmospheric air to remove VOC and organics
easily oxidized.
COD vs. Q (specific charge)
TOC vs. Q (specific charge)
J. Muff, H. Jepsen and E. Søgaard (2011) Submitted
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Electrochemical oxidation
• Powerful oxidation technique of toxic, bioincompatible
organic pollutants
– Organo-phosphoric pesticides
– PAHs
– Pharmaceutical waste
Concluding remarks
• Attention is needed concerning byproducts
– Prolonged reaction times, evaluate overall parameters
– Work needed to decrease power consumption
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Acknowledgements
• Co-authors and colleagues
• Watersafe DK Aps by Niels Erik Skjærbæk
• Zheshen Li, Aarhus University
• Students:
– Rasmus and Christian
– Gunhild, Henrik and Søren
– Henrik
– Hülia and Carina
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