Integrated Advanced Molecular Tools Predict In Situ cVOC Degradation Rates: Field Demonstration.

Chlorinated volatile organic compound (cVOC) degradation rate constants are crucial information for site management. Conventional approaches generate rate estimates from the monitoring and modeling of cVOC concentrations. This requires time series data collected along the flow path of the plume. The estimates of rate constants are often plagued by confounding issues, making predictions cumbersome and unreliable. Laboratory data suggest that targeted quantitative analysis of Dehalococcoides mccartyi (Dhc) biomarker genes (qPCR) and proteins (qProt) can be directly correlated with reductive dechlorination activity. To assess the potential of qPCR and qProt measurements to predict rates, we collected data from cVOC-contaminated aquifers. At the benchmark study site, the rate constant for degradation of cis-dichloroethene (cDCE) extracted from monitoring data was 11.0 ± 3.4 yr-1, and the rate constant predicted from the abundance of TceA peptides was 6.9 yr-1. The rate constant for degradation of vinyl chloride (VC) from monitoring data was 8.4 ± 5.7 yr-1, and the rate constant predicted from the abundance of TceA peptides was 5.2 yr-1. At the other study sites, the rate constants for cDCE degradation predicted from qPCR and qProt measurements agreed within a factor of 4. Under the right circumstances, qPCR and qProt measurements can be useful to rapidly predict rates of cDCE and VC biodegradation, providing a major advance in effective site management.

Evaluation of Biostimulation and Bioaugmentation To Stimulate Hexahydro-1,3,5-trinitro-1,3,5,-triazine Degradation in an Aerobic Groundwater Aquifer.

Hexahydro-1,3,5-trinitro-1,3,5,-triazine (RDX) is a toxic and mobile groundwater contaminant common to military sites. This study compared in situ RDX degradation rates following bioaugmentation with Gordonia sp. strain KTR9 (henceforth KTR9) to rates under biostimulation conditions in an RDX-contaminated aquifer in Umatilla, OR. Bioaugmentation was achieved by injecting site groundwater (6000 L) amended with KTR9 cells (10(8) cells mL(-1)) and low carbon substrate concentrations (<1 mM fructose) into site wells. Biostimulation (no added cells) was performed by injecting groundwater amended with low (<1 mM fructose) or high (>15 mM fructose) carbon substrate concentrations in an effort to stimulate aerobic or anaerobic microbial activity, respectively. Single-well push-pull tests were conducted to measure RDX degradation rates for each treatment. Average rate coefficients were 1.2 day(-1) for bioaugmentation and 0.7 day(-1) for high carbon biostimulation; rate coefficients for low carbon biostimulation were not significantly different from zero (p values ≥0.060). Our results suggest that bioaugmentation with KTR9 is a feasible strategy for in situ biodegradation of RDX and, at this site, is capable of achieving RDX concentration reductions comparable to those obtained by high carbon biostimulation while requiring ~97% less fructose. Bioaugmentation has potential to minimize substrate quantities and associated costs, as well as secondary groundwater quality impacts associated with anaerobic biostimulation processes (e.g., hydrogen sulfide, methane production) during full-scale RDX remediation.