Arcadis U.S., Inc.
Dr. Monica Heintz works at the nexus of groundwater hydrology, geochemistry, and microbiology to understand, manage, and mitigate environmental impacts. Her primary focus areas are natural and enhanced biological degradation of organic constituents, and the application of statistical tools to understand, describe, and predict contaminant distribution and fate. She holds a B.S. in Geological Engineering from the Colorado School of Mines and a Ph.D. in Geological Sciences from the University of California Santa Barbara. Her Ph.D. research was on aerobic methane oxidation in climate sensitive environments including the ocean and arctic lakes. Dr. Heintz has over 6 years of environmental consulting experience with Arcadis U.S., Inc, where she leads 1,4-dioxane biodegradation research and development efforts.
Comparison of Bench-Scale Environmental Molecular Diagnostics to Pilot-Scale Data During Bioremediation of 1,4-Dioxane
The use of environmental molecular diagnostics (EMDs), specifically molecular biology tools and compound specific isotope analyses, allows for a better understanding of biological processes under natural or engineered remedial systems. However, EMD data collected from field applications can be confounding when related benchmarks are not available. Commonly, these benchmarks are developed from relevant bench-scale research. An example of this for chlorinated solvents is the work done by Lu et al. (2006) that defined the relationship between Dehalococcoides DNA in ground water and rates of reductive dechlorination at field scale by using quantitative polymerase chain reaction (qPCR), resulting in a benchmark value of 1x107 cells/L. This value is now commonly cited when interpreting similar field-scale qPCR data. 1,4-Dioxane is an emerging contaminant for which biological treatment technologies are being evaluated at the field scale. EMDs are becoming readily available to provide insight into the relevant biodegradation processes; however, related benchmarks are not available for which to compare field data.
This work includes results from bench-scale microcosms that were developed to mimic site conditions from pilot-scale testing of biological treatment technologies. At a remediation site where 1,4-dioxane is the primary groundwater constituent, cometabolic in situ biosparging and cometabolic/metabolic ex situ bioreactors were pilot tested. Related bench-scale microcosms were constructed from site soil and groundwater to monitor 1,4-dioxane biodegradation under biostimulation conditions by adding oxygen, nutrients, and/or primary substrate (i.e., propane). Similar bioaugmentation microcosms were constructed with the addition of a 1,4-dioxane metabolizing microorganism (Pseudonocardia dioxanivorans CB1190) or a propanotrophic microorganism known to cometabolically degrade 1,4-dioxane (Rhodococcus ruber ENV425).
Chemical, geochemical, genetic, and isotopic data were collected during the course of 1,4-dioxane biodegradation in the microcosms. Specifically, this included 1,4-dioxane concentrations, metabolic biomarkers, cometabolic biomarkers, and carbon-13/hydrogen-2 compound specific isotope analysis. These data start to provide the benchmark for how these EMDs change as both metabolic and cometabolic biodegradation progresses and will be compared to the field-scale data collected during the pilot testing.
In Situ Propane and Oxygen Biosparge for Cometabolic Bioremediation of 1,4-Dioxane
Enhanced in situ cometabolic biodegradation an attractive remediation strategy for 1,4-dioxane in groundwater. Because cometabolic biodegradation reactions are dependent on supply of primary substrates rather than 1,4-dioxane present in groundwater, this approach is particularly applicable when 1,4-dioxane concentrations are below what would be expected to support robust metabolic biodegradation. Over the past few years, in situ propane-linked 1,4-dioxane cometabolic bioremediation systems have been successfully applied at an increasing number of sites. Here we present a pilot-scale case study of the application of a propane-linked cometabolic biosparge approach to treatment of a 1,4-dioxane plume in a weathered bedrock environment. During this study, propane, oxygen, nutrients (diammonium phosphate), and a bioaugmentation culture (Rhodococcus ruber ENV425 provided by EOS Remediation, LLC) were supplied. Compressed air and propane were injected into the weathered bedrock at up to 35 percent of the lower explosive limit (LEL) and 3 cubic feet per minute for 11 to 12 hours per day into each of two sparge wells. Success with this bioremediation approach is predicated on effective delivery of propane and oxygen, achieving substrate distribution at levels that support biodegradation rates necessary to achieve remediation goals. In aerobic bioremediation systems, oxygen supply must be sufficient to overcome demand from non-target substrates and support the biodegradation reactions of interest. Additionally, with the cometabolic approach, the potential for competitive inhibition of 1,4-dioxane biodegradation by excess propane must be balanced with the need to supply sufficient propane to support ongoing microbial growth. During the pilot study, 1,4-dioxane concentrations decreased by up to 98 percent at monitoring well locations within the test area. However, differences in substrate concentrations achieved at monitoring points across the study are, and corresponding differences in efficacy of 1,4-dioxane treatment, highlight the importance of well-engineered substrate distribution for remedy success. Full-scale design details based on pilot study results will be presented.