Design and implementation of tests to verify feasibility of different remediation technologies at a complex petrochemical site

BTEXs are prevalent contaminants at petrochemical sites, posing significant environmental and health risks due to their toxicity and mobility in soil and groundwater. This thesis examines the use of a commercial colloidal activated carbon (CAC) as an injectable reactant in the form of a water-based colloidal suspension, which is injected into the contaminated aquifer forming a treatment zone, and acts by adsorbing the BTEX present in groundwater, immobilizing them. The applications of CAC in environmental remediation are increasing in number thanks to its high surface area and strong adsorptive capacity. Conducted under the supervision of the Groundwater Engineering Group at Politecnico di Torino and Arcadis in Germany, this research included laboratory tests aimed at assessing the CAC colloidal stability and mobility in porous media, identifying 1 g/l as the optimal concentration for testing. Experiments were also conducted with NaCl added in varying concentrations to investigate the effects of ionic strength on colloidal stability, aggregation behavior, and adsorption efficiency. Additional tests were performed in deionized water (DIW) as well as in tap water. The analytical techniques adopted for the characterization of the CAC suspensions included scanning electron microscopy (SEM), CPS disc centrifugation, dynamic light scattering (DLS), ultraviolet-visible (UV-Vis) absorption spectroscopy. Column tests were conducted to study the CAC mobility in the porous medium. The characterization of the CAC particles in terms of morphology and size revealed that the studied CAC is predominantly composed of particles having a size in the range 0–50 µm. Small size is expected to correspond to a favorable surface area-to-volume ratio (facilitating effective BTEX adsorption) and expected good mobility in the porous medium, making the studied CAC a potential candidate for the field application. Therefore, laboratory tests were aimed at verifying these hypotheses. Further characterization revealed that increasing NaCl concentrations the average particle size (Z-average) increases, with great variability at higher concentrations. Thus, particle aggregation is occurring in the presence of salts, posing a potential issue for the application in aquifer systems characterized by a high salt content. Conversely, the CAC suspensions in DIW were observed to maintain a good colloidal stability at lower concentrations, with particle aggregation likely occurring at higher concentrations. Sedimentation tests showed a decreasing trend in C/C0 over time, suggesting that the formation of aggregates leads to a (at least partial) sedimentation. Finally, column test results revealed a partly limited mobility in the porous medium: in columns 10 cm long, less than 10% of CAC was recovered at column outlet, with most retained in the upper portion of the column. To conclude, the studied commercial CAC shows promising for in-situ BTEX remediation. The partly limited colloidal stability and mobility in the porous medium on the one hand may represent an issue for the preparation of CAC suspensions in the field, their injection and effective delivery in the target area (with a likely limited radius of influence) but, on the other hand, they may represent a positive aspects since they would guarantee that, once injected and delivered in the target treatment zone, the particles will not re-mobilize easily, thus preventing long-term re-mobilization of the adsorbed BTEX.