Redox Tech, LLC
Joe Rossabi has a Ph.D. in environmental engineering from Clemson University and is part owner of Redox Tech, LLC where he applies innovative remediation solutions, including chemical injection and soil blending (redox, bio-enhancement, heat, fracturing, and stabilization techniques) to soil and groundwater contamination. Previously, Rossabi was fellow engineer at Savannah River National Laboratory performing applied R&D of characterization and remediation technologies/strategies including dpt-based methods, multiphase processes (DNAPL/gas fate and transport), and passive/renewable energy methods. Rossabi is Adjunct Professor at Northwestern and Clemson Universities and has served on numerous technical advisory and review committees for EPA, DoD, DOE, and Duke Cancer.
Subsurface Farming for Remediation of Emerging, Recalcitrant Groundwater Contaminants
Widespread, and recalcitrant compounds including perfluoroalkyl substances (PFASs) are often harmful to humans and the environment at very low concentrations. PFASs are extremely difficult to address because of their increased resistance to in situ destruction and their toxicity at concentrations more than ten times lower than chlorinated solvents. To date, there are no successful in situ redox methods for several relevant PFAS. As a result, some have called for a return to pump and treat (hydraulic control) as the only viable remedial solution for these compounds. Extracting large amounts of water to address low concentrations of contaminants is not preferable but becomes more reasonable when contaminants can be concentrated and pumping optimized. A combined strategy is needed that will concentrate PFASs or other recalcitrant contaminants at specific locations in the subsurface where they can be periodically removed before reaching sensitive receptors. A subsurface farming approach where microorganisms that can sorb contaminants will be grown, nurtured, and periodically harvested, could be useful. We have been extremely successful in enhancing the growth of in situ organisms that can destroy some contaminants, now we should move to the next phase of husbandry – harvesting. Unlike most inorganic media, organisms can be readily manipulated to change phase and attachment in subsurface environments so they can be recovered in the fluid phase. In addition, organisms can be selected and engineered for optimal sorption characteristics. Although the pursuit of novel in situ destruction techniques should be continued, it is prudent to develop this alternative strategy even if only as an interim measure to complement other physical, chemical, and biological techniques that have yet to be invented for particular emerging contaminants. The advantages and challenges of using the subsurface bacterial husbandry approach will be discussed in the context of historical and current alternatives for PFAS and other emerging contaminants. Perfluorinated compounds are recalcitrant to electron transfer reactions because of both their shape and very strong carbon/fluorine bonds. Although some have reported success in treating specific aqueous PFAS in the laboratory, there have been few successful field trials. Laboratory trials found much lower kinetics and overall degradation likely due to radical scavenging by other components in soil. The degradation pathways are complicated often initiated by radical oxidation and require large molar ratios of oxidant, long reaction times, and reliable methods of producing radicals, all of which can be difficult to produce in the subsurface. Until more effective treatment approaches emerge, these compounds will require thoughtful and combined approaches likely dominated by methods to limit spread or isolate/contain hotspots. There have been many technological advances since the first days of pump and treat including accurate field analytical methods; the emergence of effective in situ chemical and biological amendments; and cost-effective access techniques. In addition, conceptual advances including better modeling techniques, the importance of combining methods in both space and time, and the value of stakeholder communications have all improved environmental remediation efforts and should guide us until we develop more direct methods to address PFAS and other emerging contaminants.