Effect of hydraulic gradient on the optimal cost of in-situ groundwater bioremediation

In the recent times, simulation-optimization (S/O) models are used to design the optimal in-situ bioremediation system for groundwater problems with constant hydraulic gradient. In such problems, the main objective is to achieve the maximum allowable contaminant concentration within a selected remediation period at a minimum cost. At a relatively higher hydraulic gradient, the contaminant moves faster towards the monitoring wells near the aquifer boundaries, therefore, in-situ bioremediation cost increases to eliminate the contaminant within the same remediation time. Here, the effect of different hydraulic gradients on the in-situ bioremediation cost of a hypothetical case study is systematically studied. The S/O model linking meshless element-free Galerkin method (EFGM) based BIOEFGM model with the particle swarm optimization (PSO) algorithm, known as BIOEFGM-PSO, is applied to estimate the optimized in-situ bioremediation cost. In this study, the different hydraulic conditions are created by changing the head values at the downstream boundary. The different combinations of injection and extraction wells are also tested to satisfy the water quality constraints for different gradient conditions.  The results of the above S/O model showed that in-situ bioremediation cost increases with an increase in hydraulic gradient, and more wells are required for remediation within the same duration under a higher hydraulic gradient.