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 SymposiumPittsburgh, PA - September 29, 2010
Project participants
U.S. Department of Energy National Energy Technology Laboratory
Chevron Clemson University
Constructed wetland treatment systems
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; notbuilt for wetland restoration or wildlife habitat
Cost savingsTreatment wetlands save $6 million in construction costs compared to conventional systems and $0.4 million in operating costs annually
Measured removal rates:% removal Outflow Conc.
Se 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
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
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
Transformations Photolysis Hydrolysis Oxidation Reduction Biotransformation/
biodegradation
Transfers 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); organochloridechemicals subject to dehalogenation
Biotransformation/biodegradation
Presence of organisms and enzymes capable of transforming targeted constituents
Biodegradable organics
Rodgers and Castle (2008)
Reducing pathway
Organic-rich sediment Metals removed by
binding to organic detritus. Decomposition results in negative redox conditions (Eh ≤ -150 mV) and metal-sulfide precipitate in presence of sulfur.
Schoenoplectus californicus C.A. Meyer
Oxidizing pathway
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
Divalent metals (Cd, Cu, Pb, Zn) Metalloids (As, Se) Oil and grease Post-RO (Ammonia)
Pilot-scale CWTS design: COCsand biogeochemical treatment pathways
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
A) Subsurface flow series
B) Free water surface seriesA
B
Pilot-scale CWTS: PW with oil & grease
Pilot-scale CWTS: PW with oil & grease
0
10
20
30
40
50
0 1 2 3
O&
G c
once
ntra
tion
(m
g/L
)
Irrigation & Livestock: 35 mg/L
Cell
Oil & Grease removal
Pilot-scale CWTS: PW with metalloids
Control
Sucrose
Aquasmart
Pilot-scale CWTS: PW with metalloids
Se removal
Pilot-scale CWTS: post-RO produced water
Pilot-scale CWTS: post-RO produced water
Pilot-scale CWTS: post-RO produced water
0
5
10
15
20
25
-8 42 92 142 192
Hydraulic Retention Time (h)
Am
mon
ia C
once
ntra
tion
(mg/
L) Sampling Period 1 CtrlSampling Period 1 ExpSampling Period 3 CtrlSampling Period 3 ExpSampling Period 5 CtrlSampling Period 5 ExpReuse Guideline
Ammonia removal
480 96 144 192
Summary of pilot-scale results 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
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
Questionsand
discussion
