Parameterization of modeling subsurface hydrocarbon contamination and biosurfactant enhanced remediation processes

Subsurface hydrocarbon contamination caused by accidental spills or operational leakages of petroleum products is a global environmental concern. In order to cost-effectively and eco-friendly recover the contaminated sites, biosurfactant enhanced aquifer remediation (BSEAR) technologies have become a popular subject in both research and practice. However, the inherent uncertainties and complexities of the subsurface systems make it challenging in numerical simulation of the hydrocarbon transport and fate as well as remediation processes. Efforts in developing more efficient and robust parameterization approaches for such modeling purpose, therefore, are highly desired. This research aims to help fill the gap by developing a novel hybrid stochastic – design of experiment aided parameterization (HSDP) method for modeling BSEAR processes. The method was developed and tested based on an integrated physical and numerical modeling system comprised of a set of intermediate scale flow cells (ISFCs) and a numerical simulator named BioF&T 3D. Generally, the HSDP method was performed by: 1) building the design of experiment (DOE) models based on screened parameters and defined responses, which could reflect the goodness of fit between observed and simulated data; 2) identifying the and interactions among parameters and their significance; 3) optimizing the DOE predicted responses; 4) introducing stochastic data within reduced intervals based on the optimized parameters; 5) running Monte Carlo simulation to find the optimal responses with the corresponding combinations of parameters. The flow cell tests proved that the HSDP method could improve both efficiency and robustness of modeling parameterization and significantly reduce the computational demand without compromising the effectiveness in quantifying parameter interactions and uncertainties. Furthermore, a specific lab synthetized surfactin was applied in this study. The effect of dissolution enhancement was observed from parallel flow cell experiments especially during the first 12 hours following the initial hydrocarbon release. The HSDP method was demonstrated to be capable of advancing BioF&T 3D, which lacks the capacity of simulating surfactant. By incorporating the HSDP method, the BSEAR processes were effectively simulated with a satisfactory overall goodness of fit (R² = 0.76, 0.81, 0.83, and 0.81 for benzene, toluene, ethylbenzene, and xylene, respectively). The enhanced dissolution effect was also reflected in the modeling parameterization by increasing the first 12 hours hydrocarbon loading ratio (12LR) compared to non-biosurfactant processes. This research developed a new parameterization method HSDP, which is capable of revealing interactions of parameters, as well as quantifying their uncertainties, in a robust and efficient manner. Also, using this method, this study initiated the attempts to advance simpler numerical models in simulating complicated BSEAR processes, which is particularly attractive for the potential applications in practice

Application of computational fluid dynamics to the biopile treatment of hydrocarbon contaminated soil

Biopiles are a common treatment for the ex-situ remediation of contaminated soil. Much research has been carried out on understanding and modelling of bioremediation techniques related to biopiles, but hitherto no study has attempted to model the effect on a biopile by its ambient surroundings. A hydraulics-based approach to simulating a biopile in the context of its ambient surroundings is presented in this study, taking into account physical, chemical and biological processes within the pile, external conditions of wind and temperature, the location of aeration pipes and venting pressure, and considering the spatial distribution of treatment as well as contaminant within the pile. The simulation approach was based upon a fluid flow model which couples Eulerian multiphase flow model and Darcy’s Law for immiscible fluid flow through porous media, a species transport model integrating advection, diffusion/dispersion and biodegradation, and a heat transfer model considering the interphase temperature equilibrium. A Computational Fluid Dynamics (CFD) system has been developed to solve this set of mathematical models by applying the commercial CFD package FLUENT, and various trial simulations have been carried out to examine the potential of the hydraulics approach for practical applications. The simulation produces reasonable results: the biodegradation process relates to the temperature within the pile, and the temperature in turn relates to wind speed and aeration details; due to the various fluid flow patterns, the contribution of each remediation mechanism (contaminant loss to atmosphere via pile surface, contaminant loss to aeration pipe and biodegradation) varies according to the aeration method; contaminant interphase transfer between different pairs of phases have greatly different impacts on contaminant removal. A number of counter-intuitive results are presented, indicating that simulations of this type will give valuable insight into the practical design of biopiling systems. The simulation system also allows the total environmental footprint of biopiling to be considered, examining not just degradation of contaminant but also its removal via volatilization and the energy used in heating air for venting. Further, the application of the approach formulated in this study is not limited to biopiles, but can also be expanded to related in situ bioremediation techniques

Modeling soil pile bioremediation

A model is presented for the analysis of bioremediation applied to an ex situ soil pile. The approach is based on the remediation of a pile containing the contaminated soil, which has been excavated from its original location, placed atop a bottom liner system and encapsulated with an impermeable cover. The liner system contains and isolates the contaminated soil and provides process control ports for injecting or withdrawing liquids or gases. The model is designed to accommodate aerobic and/or anaerobic metabolism of two classes of organic contaminants for which metabolic rates are significantly different. The model is also designed to accommodate nutrient stimulation and/or toxic inhibition of aerobic or anaerobic metabolism of either class of organics. The model presented here, together with a domain flow model which provides the convective transport velocity vector field, is a self-contained package of analyzing soil pile bioremediation. However, the model is also one component of an ongoing effort to analyze sequential ex situ treatment processes. Ultimately, this will be used in conjunction with models analyzing soil vapor extraction, bioventing, soil leaching, etc. to determine an optimum sequence configuration and operating strategy for remediating complex soil contaminatio