An integrated evaluation of bioenhanced in situ LNAPL dissolution.

Performance evaluation of in situ bioremediation processes in the field is difficult due to uncertainty created by matrix and contaminant heterogeneity, inaccessibility to direct observation, expense of sampling, and limitations of some measurements. The goal of this research was to develop a strategy for evaluating in situ bioremediation of light nonaqueous-phase liquid (LNAPL) contamination and demonstrating the occurrence of bioenhanced LNAPL dissolution by: (1) integrating a suite of analyses into a rational evaluation strategy; and (2) demonstrating the strategy's application in intermediate-scale flow-cell (ISFC) experiments simulating an aquifer contaminated with a pool of LNAPL (naphthalene dissolved in dodecane). Two ISFCs were operated to evaluate how the monitored parameters changed between a "no bioremediation" scenario and an "intrinsic in situ bioremediation" scenario.

Predictions of bioenhancement of nonaqueous phase liquid ganglia dissolution using first- and zero-order biokinetic models.

The bioenhanced dissolution of nonaqueous phase liquid (NAPL) contaminants that occurs as a result of an increased concentration gradient is influenced by several factors, including the biokinetics. This is important because available data suggest that at typical NAPL source zone concentrations, descriptions of dissolution bioenhancement may require kinetic expressions ranging from first- to zero-order. In this work, an analytical model for the bioenhancement factor, E, is developed for NAPL ganglia dissolution with zero-order kinetics, and compared to a model for E with first-order kinetics.

Laboratory-scale in situ bioremediation in heterogeneous porous media: biokinetics-limited scenario.

Subsurface heterogeneities influence interfacial mass-transfer processes and affect the application of in situ bioremediation by impacting the availability of substrates to the microorganisms. However, for difficult-to-degrade compounds, and/or cases with inhibitory biodegradation conditions, slow biokinetics may also limit the overall bioremediation rate, or be as limiting as mass-transfer processes. In this work, a quantitative framework based on a set of dimensionless coefficients was used to capture the effects of the competing interfacial and biokinetic processes and define the overall rate-limiting process.

A quantitative framework for understanding complex interactions between competing interfacial processes and in situ biodegradation.

In situ bioremediation of contaminated groundwater is made technologically challenging by the physically, chemically, and biologically heterogeneous subsurface environment. Subsurface heterogeneities are important because of influences on interfacial mass transfer processes that impact the availability of substrates to microorganisms. The goal of this study was to perform a "proof-of-concept" evaluation of the utility of a quantitative framework based on a set of dimensionless coefficients for evaluating the effects of competing physicochemical interfacial and biokinetic processes at the field scale.

Effects of temperature on bacterial transport and destruction in bioretention media: field and laboratory evaluations.

Microbial activities are significantly influenced by temperature. This study investigated the effects of temperature on the capture and destruction of bacteria from urban stormwater runoff in bioretention media using 2-year field evaluations coupled with controlled laboratory column studies. Field data from two bioretention cells show that the concentration of indicator bacteria (fecal coliforms and Escherichia coli) was reduced during most storm events, and that the probability of meeting specific water quality criteria in the discharge was increased.

The capture and destruction of Escherichia coli from simulated urban runoff using conventional bioretention media and iron oxide-coated sand.

The performance, sustainability, and mechanisms of bacterial removal from stormwater runoff by bioretention systems are poorly understood. The potential for removal of microorganisms in bioretention systems was evaluated using column studies and simulated urban stormwater runoff. Conventional bioretention media (CBM) removed 82% of Escherichia coli O157:H7 strain B6914 cells; iron-oxide coated sand (IOCS) significantly enhanced capture, with 99% efficiency.

Modeling the effects of microbial competition and hydrodynamics on the dissolution and detoxification of dense nonaqueous phase liquid contaminants.

The real significance and engineering potential for bioenhanced dissolution of chlorinated ethene dense nonaqueous phase liquid (DNAPL) contaminants are currently not well understood, in part because they can be influenced by a complex set of factors, including microbial competition for growth substrates. Mathematical simulations were performed to evaluate the effects of competition between Dehalococcoides ethenogenes and Desulfuromonas michiganensis for the electron acceptor tetrachloroethene (PCE) on the distribution of dehalorespirers, PCE dissolution, and the extent of PCE detoxification. The modeling results demonstrate that the outcome of competition between populations for growth substrates can have a significant impact on bioenhancement and, thus, on DNAPL source zone longevity and identify the key factors in determining the outcome of competition and its effects on DNAPL dissolution.

In situ bioremediation in heterogeneous porous media: dispersion-limited scenario.

A quantitative framework based on a set of dimensionless numbers was developed to capture the effects of competing interfacial and biokinetic processes and define limits on the application of in situ bioremediation. An integrated numerical modeling and experimental approach was utilized to evaluate the quantitative framework. Experiments were conducted to examine the transport and biodegradation of naphthalene in a saturated, heterogeneous intermediate-scale flow cell with two layers of contrasting hydraulic conductivities.

Sustainable oil and grease removal from synthetic stormwater runoff using bench-scale bioretention studies.

One of the principal components of the contaminant load in urban stormwater runoff is oil and grease (O&G) pollution, resulting from vehicle emissions. A mulch layer was used as a contaminant trap to remove O&G (dissolved and particulate-associated naphthalene, dissolved toluene, and dissolved motor oil hydrocarbons) from a synthetic runoff during a bench-scale infiltration study. Approximately 80 to 95% removal of all contaminants from synthetic runoff was found via sorption and filtration.

Engineered bioretention for removal of nitrate from stormwater runoff.

A bioretention unit is a simple, plant- and soil-based, low-impact treatment and infiltration facility for treating stormwater runoff in developed areas. Nitrate, however, is not attenuated in conventional bioretention facilities. Thus, this study systematically evaluated a reengineered concept of bioretention for nitrate removal via microbial denitrification, which incorporates a continuously submerged anoxic zone with an overdrain.

Bioenhancement of NAPL pool dissolution: experimental evaluation.

Experiments were conducted to quantify nonaqueous phase liquid (NAPL) pool dissolution and its enhancement by in situ biodegradation. The experiments were performed using square cross-section, glass-bead packed column reactors with a small pool of a toluene-in-dodecane mixture (toluene mole fraction, X(tol) approximately 0.02 or 0.

Kinetics of phenol and chlorophenol utilization by Acinetobacter species.

Although microbial transformations via cometabolism have been widely observed, the few available kinetic models of cometabolism have not adequately addressed the case of inhibition from both the growth and nongrowth substrates. The present study investigated the degradation kinetics of self-inhibitory growth (phenol) and nongrowth (4-chlorophenol, 4-CP) substrates, present individually and in combination. Specifically, batch experiments were performed using an Acinetobacter isolate growing on phenol alone and with 4-CP present.