Integrated Hydrothermal Carbonization and KOH Activation of Mechanically Treated Municipal Solid Waste: Optimization of Adsorbents for BTEX Removal from Water

The sustainable management of municipal solid waste (MSW) remains a pressing challenge, particularly for the under-sieve fraction generated during mechanical treatment (MT), which is currently landfilled. This study proposes an integrated valorization route involving hydrothermal carbonization (HTC), followed by potassium hydroxide (KOH) activation to convert MT-MSW into activated hydrochar (AHC). Response surface methodology (RSM) was employed to systematically investigate the synergistic effects of activation temperature (500–700 °C) and KOH/hydrochar impregnation ratio (0.5–1.5) on specific surface area and BTEX (benzene, toluene, ethylbenzene, and xylenes) removal efficiency from water. Results demonstrate that moderate activation severity (600 °C, KOH/HC = 1.0) promotes the formation of a predominantly microporous structure (BET surface area: 440.7 m2/g; micropore area: 363.9 m2/g), achieving a total BTEX removal of 84.7%. RSM analysis showed that both activation temperature and KOH/hydrochar ratio significantly affected AHC yield and surface area, whereas activation temperature was the main statistically significant factor governing BTEX removal. Overall, the developed models provide a predictive framework for tailoring AHC properties by optimizing the activation conditions. These findings establish a viable circular solution for the upcycling of urban waste streams into engineered adsorbents for environmental remediation.