Emerging Contaminants Summit

Spring 2020

harePaul Hare
Sr. Technical Director

Paul W. Hare, CPG, PG is a Senior Technical Director in OBG's Applied Sciences group, working out of the Albany, NY office. He has over 30 years of experience as a Hydrogeologist, Project Manager and Program Manager working on environmental remediation projects, including more than 20 years as an Owner. Mr. Hare co-leads OBG's Emerging Contaminants team, which currently focuses on 1,4-dioxane and perfluorinated compounds.MBA, Rensselaer Polytechnic Institute, MS, Geology, Pennsylvania State University, BS, Geology & Agronomy, Pennsylvania State University



1,4-Dioxane Degradation in an Aerobic, Fixed-Film Bioreactor with Toluene, Other Volatile Organics and Phenolics in the Influent

Paul Hare, Mark Harkness, Paul D’Annibale (OBG) Don Sauda (ARCADIS), Lew Streeter (GE)

A treatment system was designed and constructed at a federal Superfund site in the Northeastern U.S. to treat groundwater. This system allowed off-site hauling (100s of trucks per year) to be discontinued, and facilitated the addition of five new recovery wells.

Groundwater is impacted by several V0Cs, 1,4-dioxane and, to a lesser extent, SVOCs (largely phenolics). VOCs in the influent are dominated by toluene, benzene, TCE, cDCE and chlorobenzene, but other volatiles are also present, including acetone, vinyl chloride and xylenes.

The treatment system has several unit processes, one of which is a fixed-film, aerobic bioreactor. The bioreactor was included in the system to remove many of the degradable constituents and minimize the use of liquid- and vapor-phase carbon that are associated with downstream processes. The reactor was not intended for 14Dx degradation; an advanced oxidation unit is present downstream, and its principle purpose is the destruction of 14Dx to acceptable levels.

The treatment system has been in routine operation for more than two years. The concentration of 14Dx in the influent has averaged more than 200 ug/L during this period. Based on the results of process monitoring performed within the system, an average reduction of 20% has been observed before the advanced oxidation unit. The average percent reduction of 14Dx increased over time after system start-up, with some reductions over 30% observed in the last year. 14Dx reduction was suspected to be due to aerobic biodegradation within the bioreactor, perhaps via toluene co-metabolism given the dominance of that constituent in the influent (with concentrations above 5,000 ug/L). Phenolics are also present in the influent, but at much lower concentrations.

Samples were collected from the influent and effluent of the bioreactor for analysis of seven microbiologic targets associated with the metabolic and co-metabolic degradation of 14Dx. The results for six monooxygenase targets were positive and significant; only the results for aldehyde dehydrogenase were insignificant. To further explore the reduction of 14Dx concentrations across the fixed-film reactor, samples were collected for two-dimensional compound-specific stable isotope analysis.

This presentation will present the results of the specialty analyses that were performed to demonstrate that the reduction of 14Dx across the fixed-film reactor is due to biodegradation. The treatment system will be briefly described, and the chemical characteristics of the influent will be presented, with focus on the constituents that the bioreactor was installed to address and the constituents that have been shown to be inhibitory to the degradation of 14Dx.

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