Design of in-situ microbial filter for the remediation of naphthalene

The in-situ microbial filter (ISMF) is a specific application of in-situ bioremediation (ISB) for the treatment of groundwater contaminated plumes. The ISMF filter consists of an in-situ reactor, composed of sand mixed with non-indigenous microorganisms, that is placed ahead of migrating contaminant plumes and removes contaminants by biological and abiological processes. This paper presents the results of an experimental study investigating the remediation of naphthalene contaminated water through a lab scale ISMF. Mathematical modeling was performed to determine the optimum dimensions and configuration of the ISMF, and to stimulate the migration of naphthalene through the ISMF. Soil column tests were carried out to determine the biomass concentration and hydraulic conductivity to attain effective biodegradation within an ISMF. The optimum biomass concentration was determined to be 1.4 mg VSS/g sand and the optimum hydraulic conductivity was determined to be approximately 1×10−5 m/s. FLOTRANS, a two-dimensional finite element hydrogeological model based on the advection-dispersion equation, was used to illustrate the effect of different filter and barrier configurations on the discharge through the filter and to stimulate naphthalene migration through an ISMF. Experimental results and the mean simulation values obtained through Crystal Ball®, a forecasting and risk analysis program, were used as the input parameters for the FLOTRANS model. Optimum dimensions and configurations of the filter were determined for effective remediation of naphthalene. Modeling results indicated that an ISMF, with the flow and transport properties determined in this study, has the capacity to substantially attenuate naphthalene contaminated groundwater. A sensitivity analysis was performed using Crystal Ball® to determine the relative influence of the basic parameters from the advection–dispersion equation on the contaminant concentration.