R01 2015 SRP Research WebinarSession II

February 9, 2015

Dual-Biofilm Reactive Barrier for Treatment of Chlorinated Benzenes at Anaerobic-Aerobic Interfaces in Contaminated Groundwater and

Sediments

Ed Bouwer, Johns Hopkins UniversityMichelle Lorah, U.S. Geological SurveyNeal Durant, Geosyntec ConsultantsAmar Wadhawan, Geosyntec Consultants

Chlorobenzenes• 12 congeners containing 1-6 substituted Cl covalently bonded

to C (MCB, 3 x DCBs, 3 x TCBs, 3 x TeCBs, PeCB, HCB)• Higher CBs have low aqueous solubility and higher

partitioning into sediment. Less mobility in aqueous environment• Lower CBs have higher aqueous solubility and can be volatile.

Higher mobility in aqueous environment• Biodegradation and photolysis are only major degradation

pathways

…

CB Biodegradation Pathways• Aerobic

• CBs utilized as C and e- donor• Oxygen required as terminal e- acceptor• Viable degradation pathway for TeCB and lower• Mineralization to CO2 and HCl• Lower CBs degrade at higher rates

• Anaerobic (dehalorespiration)• Reductive dehalogenation to lower CBs• Separate e- donor required• CB can serve as a terminal electron acceptor, cleaving Cl• Higher CBs tend to have higher rates of reductive dehalogenation

CBDB1 dehalorespiring bacteria

Fields & Sierra-Alvarez, 2008. Adrian et al. 2000

Field Site: Standard Chlorine of Delaware

• New Castle, DE• Former chlorobenzene manufacturer from 1966 - 2002• 65 acre site in heavily industrialized area• 2 Major chemical spill events

• 1981 railroad tanker car CB spill• 1986 VOC tank spills (569,000 gallons)

• EPA managed superfund site since 2002• Abuts Red Lion Creek, part of Delaware River watershed• Potential for human exposure to CB contaminants through surface

waters, groundwater, wetlands, and bioaccumulation in fish and other aquatic organisms

• Extensive remediation and containment at main industrial site, but not in wetland area

http://www.epa.gov/reg3hscd/npl/DED041212473.htm

Project Impetus

• Aquifers below wetland already contaminated with DNAPL CBs• Total CB concentration in groundwater as high as

75 mg/L• Deep Potomac Aquifer is a drinking water source

outside of site• Half of water flow to Red Lion Creek is from

shallow Columbia Aquifer• Want to develop and optimize in-situ flow-

through system to remove and degrade CBs from water flowing to surface• Degradation must be complete. Partial

dechlorination of higher CBs to MCB and benzene potentially more hazardous than original parent compounds SCD Site. Wetland area highlighted red

Lorah et al. 2014

Dual Biofilm Reactive Barrier• Combines a sorbent matrix for

sequestration with dechlorinating biofilms for degradation

• Leverages varying redox conditions and oxygenic gradients of wetland sediment to support both aerobic and anaerobic biofilms simultaneously

• Granular activated carbon (GAC) utilized as proposed sorbent and growth surface

• Anaerobic consortium WBC-2 (isolated by Lorah at USGS) to break down higher CBs

• Aerobic culture enriched from SCD site to break down lower CBs

Changing Paradigm

Previous paradigm for chlorinated VOCs:•Aerobic oxidation requires measurable oxygen•Anaerobic oxidation must be responsible for degradation of VOCs at anaerobic plume fringes Microbial

Mineralization of

Dichloroethene and

Vinyl Chloride under

Hypoxic Conditions

Perils of Categorical

Thinking: “Oxic/Anoxic”

Conceptual Model in

Environmental Remediation

Isolation of an aerobic

vinyl chloride oxidizer

from anaerobic

groundwater

Concurrent and Complete Anaerobic Reduction and

Microaerophilic Degradation of Mono-, Di-, and Trichlorobenzenes

Fullerton et al. 2014

Bradley and

Chapelle 2011

Bradley 2012

Gossett 2010

Burns et al. 2013

Sustained Aerobic Oxidation of Vinyl

Chloride at Low Oxygen Concentrations

Bio-Traps:13C-labeled MCBincorporation in CO2 and Biomass (PLFA)

aerobic

Bioreactors- Total CBs+Benzene

Research Aims

• Characterize biofilm growth on GAC and quantify dechlorination activity• Assess long-term stability and removal efficiency of

reactive barrier system• Understand the effects of biogeochemical

conditions on sorption and degradation processes• Optimize barrier performance robustness and

removal efficiency

Initial Microcosm Experiments• Batch adsorption / desorption experiments to

understand interactions between CBs and GAC under natural and clean conditions• Explore effects of natural sediment and

groundwater constituents on sorption behavior• Assess bioavailability of sorbed CBs for

dechlorinating biofilms• Determine effects of biofilm coatings on sorption to

GAC

Questions?