Model-based evaluation of efficiency of electrolysis-enhanced in-situ bioremediation for trichloroethylene using tandem circulation well

Aerobic bioremediation combined with electrolytic enhancement, stimulating the indigenous subsurface microflora to degrade TCE, in the recirculating system of groundwater and solute induced by tandem circulation well (TCW) is a novel in-situ remediation method which has been gradually valued for its great application prospects due its  environmental and economic advantages. Previous investigations have been limited to few laboratory experiments, and neither the evaluation of remediation efficiency nor the improvement methods in application were fully understood. This study developed a reactive transport model for in-situ TCE bioremediation, simulating TCW-induced groundwater recirculating system, aerobic biodegradation process of TCE and electrolytic enhanced oxygen supply. A regionalized sensitivity analysis (RSA) was conducted based on the experimental data to quantify the influences of parameters, reduce the number of parameters inverted and provide the value of reactive kinetic parameters for this model. Different simulation cases were conducted to investigate influence of operating parameters and well spacing for remediation efficiency. The results show that increase in both current and pumping rate can improve the degradation efficiency but has a maximum degradation capacity due the limitation of saturated DO concentration in wellbore. Through a quantitative characterization of solute mixing, the model demonstrated an optimal operating parameters index (α_optimal), helping to find the optimal ratio of current and pumping rate. The results of the influence of well spacing indicate that too close an injection/extraction well distance is detrimental to degradation efficiency and the current and pumping rate need to increase in the same proportion with the increasing remediation area to remain the optimal efficiency.