Evaluation of enhanced trichloroethylene and perchloroethylene adsorption in simulated groundwater utilizing modified walnut shell biochars.

Sustainable and cost-efficient adsorbents are crucial in environmental remediation, with biochar emerging as a promising material for such applications. This study evaluates the enhanced adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from simulated groundwater representing the U.S. Department of Energy's (DOE) Savannah River Site (SRS) using modified walnut shell biochars. Alkali intercalation and acid exfoliation (ICE) were applied to the 'native' walnut biochar to improve surface area and pore structure, enhancing its adsorption performance. Biochars were characterized using BET surface area analysis, SEM, FTIR, and EDS to assess changes in properties pre- and post-adsorption. ICE-modified biochar exhibited a significant increase in surface area to 1180 ± 40 m2/g, representing a 168% improvement over the unmodified walnut biochar (WN9) with a surface area of 440 ± 2 m2/g. Adsorption isotherm experiments showed ICE-modified biochar achieved substantially higher Freundlich adsorption capacities (Kf), with values of 65 (mg/g)/(mg/L)1/n for TCE and 134 (mg/g)/(mg/L)1/n for PCE. In contrast, the unmodified biochar exhibited a lower Kf of 15 for TCE, with no determinate capacity for PCE in both Langmuir and Freundlich isotherm models. Adsorption performance over the 72 h reaction time showed that ICE-modified biochar achieved 85% removal of 100 mg/L TCE compared to 73% for unmodified biochar. Similarly, over the 72 h reaction time, the ICE biochar removed 95% of 100 mg/L PCE, while the unmodified biochar achieved only 46% removal, all at a 30 mg dosage. Therefore, modified walnut shell biochars showed enhanced TCE and PCE adsorption, indicating notable groundwater remediation potential.