the potential for solar-powered remediation a solar-powered centrifugal pump to promote water...

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This project is supported by Grant Award Number P42ES017198 from the National Institute of Environmental Health Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Environmental Health Sciences or the National Institutes of Health.

The Potential for Solar-Powered Remediation

Akram N. AlshawabkehCivil and Environmental Engineering

Northeastern UniversityBoston, MA

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NIEHS SRP P42 Research Program

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Content

• Relevance• Concept and Basics• Example: Hexavalent Chromium

Transformation• Research Translation• Current Effort• Summary and Acknowledgment

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RELEVANCE

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http://www.clu-in.org/greenremediation/

EPA’s strategic plan strives for cleanup programs that use natural resources and energy efficiently, reduce negative impacts on the environment, minimize pollution at its source, and reduce waste to the greatest extent possible.

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Solar Energy use at Superfund Sites: Examples

• Aerojet-General Corporation CA, Trichlorothene (TCE) and perchlorate: Use solar energy to partially meet power requirements for pump-and-treat system.

• Apache Powder AZ, heavy metals and explosives: constructed wetland system. Used a solar-powered centrifugal pump to promote water recirculation in the wetlands system.

• Crozet Orchard VA, metals and pesticides: phytoremediation. Uses solar-powered low-flow pumps to transfer water from a hill-bottom spring to a second storage tank.

• Delfasco Forge TX, TCE vapor. Use solar energy to power exhaust systems addressing TCE vapor intrusion.

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http://www.clu-in.org/greenremediation/subtab_d31.cfm�




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EPA’s Relevant Activities

• Emphasize the use of renewable energy for cleanup operations

• Developed BMP’s on clean fuels and emission technologies

• Evaluating tools for calculating environmental “footprints” of cleanup

• EPA’s 2011-2015 Strategic Plan includes continued work to reduce the energy use and environmental footprint during site investigation and remediation

Research Needs/Opportunities: Sustainable Solar-Powered “Active” Remediation

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CONCEPT AND BASICS

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Background

• In many cases, remediation is based on redoxmanipulation of groundwater for transformation and/or immobilization of contaminants

• Redox manipulation is usually achieved by injection of additives that are oxidizing or reducing; e.g., HRC, ORC, ferrous sulfate, ZVI

• Transformation occurs by chemical and/or biological processes

• Challenges: Efficiency; Sustainability; Delivery; Cost

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• Adopt electrolysis to manipulate and control groundwater redox conditions for chemical and/or biological transformation of contaminants

• Use solar panels for electric power required for electrolysis

• Treatment systems could include well injections or permeable reactive barrier systems

• Potential target contaminants:– Chromium, Arsenic, Chlorinated solvents, PAH’s, others

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Solar-Powered Remediation – Concept –


Ground Surface

_+ _

Porous Iron Electrodes

Porous (Screened) Well

Solar Panel

Contaminated Groundwater Flow

Renewable energy for “sustained” manipulation of groundwater redox conditions

Solar-Powered Remediation – Concept –

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Basics: Electrolysis

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Cathode (-)Anode (+)

2H2O - 4e- 4H+ + O2

Production of acid and Oxygen gas

4H2O + 4e- --> 4OH- + 2H2

Production of base and Hydrogen gas

dc source(Solar Panel)

Charge/Mass transfer at the electrodes (Faraday’s Law)

e-

If iron electrode,Fe(0) – 2e- Fe2+ (aq)e-


Cathode (-)Anode (+)

2H2O - 4e- 4H+ + O2

Production of acid and Oxygen gas

4H2O + 4e- --> 4OH- + 2H2

Production of base and Hydrogen gas

dc source(Solar Panel)

Charge/Mass transfer at the electrodes (Faraday’s Law)

e-

If iron electrode,Fe(0) – 2e- Fe2+ (aq)e-

Basics: Electrolysis

Soil o

r Mem

bran

e

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Example Strategy 1 – O2/H2 Production –

• H2O ½ O2 + 2H+ + 2e- (Anode)

• 2H2O + 2e- 2OH- + H2 (Cathode)

• Net reaction in a mixed electrolyte• H2O ½ O2 + H2

• Options:• Collect O2 at the anode and allow H2 to mix with GW

• Collect H2 at the cathode and allow O2 to mix with GW

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Example Strategy 2– Fe Anode Redox –

• Iron Anode: Fe(0) 2e- + Fe2+ (aq)

• Sustainable generation and delivery of Fe(II) to GW

• Chemically reducing conditions develop • Could be used in a mixed or isolated

electrode reactor

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Transformation Mechanisms

• Biological– Aerobic: by production of O2 as an electron acceptor;

e.g. PAH– Anaerobic: by production of H2 as an electron donor;

e.g. PCE

• Chemical – Reduction of hexavalent chromium – Oxidation of PAH and BTEX – Alkaline Hydrolysis: transformation of RDX

• Electrochemical– Direct oxidation at the anode or reduction at the cathode

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EXAMPLE –HEXAVALENT CHROMIUM

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Laboratory Study: Cr(VI) Reduction by Fe electrolysis

• Hypothesis:

– Electrolysis using iron electrodes (anodes and cathodes) will induce Fe(II) (and H2) dominated reducing conditions that can be manipulated for chemical reduction of Cr(IV).

• Justification:

– The reactivity is similar to reduction by ZVI (single electrode redox)

• Advantages:

– The kinetics of electrolysis and consequent redox and transformation can be controlled to optimize (accelerate or limit) the release of Fe(II)/H2 by controlling the electric current density and polarity in a 2 electrode system.

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Experimental Setup

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-200

-150

-100

-50

0

50

100

150

200

250

300

0 5 10 15 20 25

OR

P (

mV

)

Time (hour)

CathodeAnodeMixed Electrolyte

0

2

4

6

8

10

12

0 5 10 15 20 25

pH

Time (hour)

CathodeAnodeMixed Electrolyte

ORP and pH measurements under 1 mA/L using Fe electrodes for cases with separate and mixed electrolytes. Total voltage was on the order of 2 V in the separated and 0.5 V in the mixed electrolytes.

Results – Batch Samples –

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0

3

6

9

12

15

18

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0 2 4 6 8 10 12 14 16 18 20 22 24 26Time (hr)

Cr(

VI)

, mg/

L

15mA/L 7.5 mA/L 1.5 mA/L

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350 400 450

It, C/L

C/C

o

15mA/L 7.5 mA/L 1.5 mA/L

Initial Concentration = 20 mg/L

Results – Batch Samples –

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Fe2+2e_

Fe2+2e_

Fe2+2e_

6e_

6H2O

3H2

6OH _

123

33

224

2

83

43

)(OH)(CrFe

OHFeCr

O H CrOFe

+++

++

−++

−+

HOH

OH

+− + 64

6 2

42CrONa

Anode CathodeSolution (Anolyte)

−

+

OHNa

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3133

332

24

2

20

31

83432

)(OH)Fe(Cr OH -x)Fe ( xCrOHFeCrO H CrOFe

eFeFe

xx-

−++

−++−+

−+

→++

++→++

+→

Cr(VI) Transformation Mechanism

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)( IIFeJ −OHJ

2HJ

L0x

DC

rygeochemist

OHOHOH

rygeochemist

IIFeeIIFeIIFe

iiii

tcJLxxR

tc

JxxR

nRxcv

xcnD

tnc

∂∂

+−−=

=

∂

∂+−=

=

+∂∂

−∂∂

=∂∂

−−−

e0

)()(0)(

2

2

)(

-OHiwhen

)(

Fe(II)iwhen

δ

δ

x

Electrochemical Redoxunder GW Flow

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0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800

Time (hr)

C/Co

Port 1

Port 2

Anode

Cathode

Port 3

Port 4

Port 5

Port 6

Port 7

Port 8

Current density of 0.12A/m2 , Electrode spacing of 2.5 cm

No

Current

1 2 3 4 5 6 7 8Port #Flow 8 cm spacing showed similar results

Cr Redox under Flow– Sand Column Tests –

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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 24 48 72 96 120 144 168Time (hr)

C/Co

Port 3

Anode

Cathode

port 6

Port 7

port 8

Effect of Increasing flow rate – Current density of 0.12A/m2


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0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400 450

Time (hr)

C/Co

Port 1Port 2AnodecathodePort 3Port 4Port 5Port 6Port 7Port 8

No

Current

Flow rate 490 ml/day

Current density of 0.36A/m2

Electrode spacing of 2.5 cm


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RESEARCH TRANSLATION

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• Assume average groundwater flow rate = 10 cm/day.• Assume Average chromium concentration = 5 mg/l, • Cr flux = 0.5 g/m2.day or 0.01 mole/m2.day. • Required Fe(II) flux [JFe(II)] = 0.03 mole/m2.day• Required electric current density (I=2JFe(II)F/0.75) = 0.09 A/m2. • 50W solar panel (few $100) with 3 Amps (20 Volt) would cover

a cross sectional area of more than 30 m2 of flowing groundwater.

• Assumptions: – 3 moles of Fe(II) are required per 1 mole of Cr(VI).

– 75% electrolysis efficiency

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Practical Issues:How Much Energy - Example?

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Potential Challenges

• Precipitation and changes in hydraulic conductivity– Function of electric current/flow rate, GW chemistry

• Passivation:– Less likely, but use polarity reversal if it occurs

• pH changes in GW– Function of electric current/flow rate, GW chemistry

• Delivery to contaminated zones

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Process design is critical


Ground Surface

_+ _



Solar Panel


Ground Surface

_ +_



Fe(II) Front

H2 & OH-

Front

Solar Panel


Implementation Strategies – Examples –


Bae et al., 1995 McCarty et al., 1998; Goltz et al., 2009

Implementation Strategies – Examples –

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CURRENT EFFORT

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PI/Co-Director: Akram N. Alshawabkeh, Professor, Civil and Environmental Eng., NUCo-Director: José F. Cordero, Dean, Graduate School of Public Health, UPR-MC

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PROTECT Focus

• Role of exposure to contamination on preterm birth

• Contamination in Puerto Rico (14 Superfund site + 2 Proposed)

• karst aquifers • Target Contaminants: Chlorinated

Solvents and Phthalates

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PROTECT Project 5Alshawabkeh, Padilla, Podlaha, Vesper

• Goal: Developing green remediation technologies based on conversion of solar energy into electrochemical redox in groundwater

• Focus on chlorinated solvents in karst aquifers• Proposed transformation pathways:

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SUMMARY AND ACKNOWLEDGMENT

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Summary

• Solar energy conversion into electrochemical redox in groundwater can be a green and sustainable remediation technology

• Oxidizing or reducing groundwater conditions can be engineered

• Conditions can be developed for chemical, biological and/or electrochemical transformation

• Fe anodes would lead to reducing conditions causing reduction and immobilization of chromium

• Transformation of chlorinated solvents by iron electrodes is being evaluated in karst aquifers

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Acknowledgment

• PRoTECT Team and Advisory Committees• CenSSIS (Center for Subsurface Sensing

and Imaging Systems) Team• NIEHS SRP Award Number P42ES017198• NIEHS SRP Team • Post-docs, Students and Teachers

– Hussam Sarahney, David Gent, Xuhui Mao, Ali Ciblak, Sara Barbuto, Samantha Kendrick, Susan Agger, Jessica Quinn, Mohammad Amiri, Reza Ghasemizadeh, Naji Kasem, HatimFedllalah, Xingzhi Wu

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PROTECT Team

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Tom Ferdi Akram José Raul John Sangchul

Rita Braulio Roger Ingrid Mariah Kristin Michael Dave

the potential for solar-powered remediation a solar-powered centrifugal pump to promote water...

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