## 4 Results and Discussion
### Microbial Remediation with Chemotaxis Optimization
To address this issue, genetic engineering can be employed to enhance chemotactic bacteria. This can involve increasing their chemotaxis, making them more inclined to move towards pollutants. Additionally, they can be engineered to undergo rapid mutations, facilitating their adaptation to the optimal growth concentration based on pollutant concentrations in groundwater. In the model, increasing the chemotactic sensitivity coefficient \(\chi_{0}\) and setting the chemoreceptor kinetics constant \(K_{c}\) as a linearly decreasing function of time produces the cross-sectional image shown in Figure 12b. This means that during the bioremediation process, the bacteria can quickly adapt to the continuously decreasing VOC concentrations, rather than simply cultivating bacteria with the optimal growth concentration set for low concentrations of VOC. This results in a significant increase in the range of chemotactic bacteria along the pollutant concentration gradient. The total concentration of chemotactic bacteria on this cross-section reaches 428.21 mol. After extraction is stopped, chemotactic bacteria, both enhanced and non-enhanced, undergo ten years of free diffusion, yielding the cross-sectional images depicted in Figure 12c,d, respectively. In the case of enhanced chemotactic bacteria, there is a substantial presence in low-permeability areas, with a total concentration of 787.15 mol, significantly higher than the 368.24 mol observed for non-enhanced chemotactic bacteria. A profile line is taken in the low-permeability area on the cross-section. The concentrations of VOC and chemotactic bacteria are plotted along this line. Figure 13 illustrates the concentrations of VOC and chemotactic bacteria after one year of water injection, while Figure 14 shows the concentrations after ten years of bacterial free diffusion. The black line represents the concentration of VOC, with pollutant concentrations ranging from 0.005 mol/m\({}^{3}\) to 0.04 mol/m\({}^{3}\), indicating a large concentration span. The red line represents  
Figure 12: Concentration of chemotactic bacteria (cloud plot) vs. concentration of VOC (contours). (**a**) Chemotactic bacteria with reduced suitable growth concentration after one year’s time. (**b**) Chemotactic bacteria intensified after one year’s time. (**c**) Chemotactic bacteria with reduced suitable growth concentrations after ten years’ time. (**d**) Chemotactic bacteria intensified after ten years’ time. chemotactic bacteria that have not been selectively cultivated, the green line represents chemotactic bacteria selectively cultivated for low concentrations of VOC, and the blue line represents the enhanced chemotactic bacteria, as previously described, which are designed to quickly adapt to the decreasing concentrations of VOC. Following one year of injection, the concentration of enhanced chemotactic bacteria in the low-permeability zone is significantly higher than that of the other two chemotactic bacteria types. Although the chemotactic bacteria optimized for lower-concentration VOC perform slightly better than the original chemotactic bacteria, the effect is not substantial. Although the former have been optimized for low concentrations of VOCs and are initially active in the high-permeability area with high VOC concentrations when injected with water, the bacterial activity is not high in the early stages of treatment. The latter, however, show a lack of sensitivity to low concentrations of VOC, resulting in decreased bacterial activity in the later stages of the treatment process. After ten years of bacterial free movement, enhanced chemotactic bacteria exhibit a clear trend towards areas with higher VOC concentrations. The efficacy of the other two non-enhanced bacteria types in chemotaxis within the low-permeability area remains limited.