Mesoporous activated carbon shows superior adsorption affinity for 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol in water

Increasing cannabinoid use with the incipient favorable public discourse raises concerns about their environmental release and potential impacts. Concentration of common cannabinoids and their metabolites (e.g., THC and THC-COOH) are already detected in source waters and engineered water systems across the globe with a rising trajectory. This study examines the adsorption of THC and THC-COOH onto activated carbons in surface water-relevant concentrations and investigates the effect of carbon’s physicochemical properties. At higher equilibrium concentration (i.e., C_e > 300 µg/L), adsorption of cannabinoids correlates with the sorbent-specific surface area. On the contrary, at lower concentrations (i.e., C_e = 0.1–100 µg/L), cannabinoid adsorption was predominantly controlled by pore size of the carbon. More specifically, when the surface area was not limited (i.e., dilution conditions), cannabinoid molecules appeared to have preferably attached within the mesopores. The adsorption mechanism deciphered in the study will facilitate in selection of commercial activated carbon to remove cannabinoids in drinking water treatment systems. This work will also provide a baseline for further research on removal of other cannabinoids (e.g., CBD), other structurally relevant drugs, their metabolites, and reaction byproduct from engineered treatment systems.