Pilot-Scale Constructed Wetland
Systems for Treating
Energy-Produced Waters
James Castle, Zack Wasser, John Rodgers, Mike Spacil, Bethany Alley,
Jennifer Horner, and Michael Pardue
Clemson University
2010 Water/Energy Sustainability Symposium
Pittsburgh, PA - September 29, 2010
Project participants
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U.S. Department of Energy
National Energy Technology Laboratory
Chevron
Clemson University
Constructed wetland treatment systems
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Designed to treat constituents in impaired water
to extend opportunities for beneficial use
Goal: remove targeted constituents from
aqueous phase and partition to sediments in
non-bioavailable forms
Permitted as “wastewater”
treatment systems; not
built for wetland
restoration or wildlife
habitat
Cost savings
Treatment wetlands save
$6 million in construction
costs compared to
conventional systems and
$0.4 million in operating
costs annually
Measured removal rates:
Se
% removal
Outflow Conc.
90%
0.15 mg/L
Hg
95%
0.019 mg/L
As
96%
0.03 mg/L
TSS
94%
31 mg/L
Project purpose
Develop constructed wetland systems for
treatment and beneficial use of oil and gas
produced waters
Project scope
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Phase I: Assess environmental factors
associated with produced waters
Phase II: Design, construct, and measure
performance in a pilot-scale wetland
treatment system
Phase III: Design, construct, and measure
performance in a demonstration-scale
wetland treatment system
Approach
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Identify chemical, physical, and risk
characteristics of produced waters
Determine reuse and discharge criteria
Develop treatment performance goals
Identify biogeochemical treatment processes
(pathways) and conditions to achieve these
processes
Design and construct system
Measure treatment performance
Treatment processes
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Transformations
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Photolysis
Hydrolysis
Oxidation
Reduction
Biotransformation/
biodegradation
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Transfers
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Sorption
Volatilization
Precipitation, settling,
and sedimentation
Bioconcentration (plant
uptake)
Transformation processes
Process
Biogeochemical conditions
Examples of constituents removed
Photolysis
Sunlight intensity and light
absorption
Low molecular weight organics
Hydrolysis
Acid, basic, or neutral
environment depending on
targeted constituents
Pesticides
Oxidation
Redox (Eh) > -50 (approx.);
pH slightly acidic to near
neutral
Organics (e.g. oil & grease); some metals
(e.g. Fe)
Reduction
Redox (Eh) < -150 (approx.);
pH near neutral to slightly
basic
Metals (e.g. Hg, Cu, Pb, Zn); organochloride
chemicals subject to dehalogenation
Presence of organisms and
enzymes capable of
transforming targeted
constituents
Biodegradable organics
Biotransformation/
biodegradation
Rodgers and Castle (2008)
Reducing pathway
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Organic-rich sediment
Metals removed by
binding to organic
detritus. Decomposition
results in negative
redox conditions (Eh ≤
-150 mV) and metalsulfide precipitate in
presence of sulfur.
Schoenoplectus
californicus C.A. Meyer
Oxidizing pathway
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Eh > -50 mV
Sandy sediment
Removal of water
soluble organics and
some metals via
oxidative pathways
Typha latifolia L.
Constituents of concern in produced water
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Divalent metals (Cd, Cu, Pb, Zn)
Metalloids (As, Se)
Oil and grease
Post-RO (Ammonia)
Pilot-scale CWTS design: COCs
and biogeochemical treatment pathways
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Divalent metals (Cd, Cu, Pb, Zn):
dissimilatory sulfate reduction
Metalloids (Se, As):
microbial reduction, co-precipitation
Oil and grease:
oxidation, biodegradation, sorption
Post-RO (Ammonia):
nitrification, denitrification
Pilot-scale CWTS: PW with divalent metals
(and LMWOs)
Pilot-scale CWTS: PW with divalent metals
Metal removal
Pilot-scale CWTS: PW with oil & grease
B
A) Subsurface flow series
B) Free water surface series
A
Pilot-scale CWTS: PW with oil & grease
O&G concentration (mg/L)
50
40
Irrigation & Livestock: 35 mg/L
30
20
10
0
0
1
Cell
2
Oil & Grease removal
3
Pilot-scale CWTS: PW with metalloids
Control
Aquasmart
Sucrose
Pilot-scale CWTS: PW with metalloids
Se removal
Pilot-scale CWTS: post-RO produced water
Pilot-scale CWTS: post-RO produced water
Ammonia Concentration (mg/L)
Pilot-scale CWTS: post-RO produced water
Sampling Period 1 Ctrl
Sampling Period 1 Exp
Sampling Period 3 Ctrl
Sampling Period 3 Exp
Sampling Period 5 Ctrl
Sampling Period 5 Exp
Reuse Guideline
25
20
15
10
5
0
-8 0
4248
9296
144
142
Hydraulic Retention Time (h)
Ammonia removal
192
192
Summary of pilot-scale results
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Pilot-scale constructed wetland treatment
systems were designed and constructed to
promote biogeochemical pathways for
treating COCs identified in produced waters
Treatment performance and conditions were
monitored in the pilot-scale CWTSs
Effective treatment was achieved: divalent
metals, oil & grease, metalloids, and
ammonia
Application of pilot-scale results
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Apply results from the pilot-scale study to
design and construct demonstration-scale
CWTS for onsite treatment of COCs
Measure treatment performance and develop
design parameters for applying the
technology to additional sites
Questions
and
discussion