R SRP Research Webinar Session 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 University Michelle Lorah, U.S. Geological Survey Neal Durant, Geosyntec Consultants Amar 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 CO 2 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, Adrian et al. 2000

Field Site: Standard Chlorine of Delaware New Castle, DE Former chlorobenzene manufacturer from 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

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 Bradley and Chapelle 2011 Bradley 2012 Gossett 2010 Burns et al Sustained Aerobic Oxidation of Vinyl Chloride at Low Oxygen Concentrations

Bio-Traps: 13 C-labeled MCB incorporation 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?