Walnut Shell Biowaste Valorization via HTC Process for the Removal of Some Emerging Pharmaceutical Pollutants from Aqueous Solutions

Abstract

This research emphasizes the performance of some eco-friendly carbon materials as hydrochars (HC) obtained by the hydrothermal carbonization (HTC) process applied to walnut shell (WS) biowaste. These materials display promising properties that can be used for environmental applications such as emerging pharmaceutical pollutant retention from water sources. Thus, three hydrochars coded HCWS1, HCWS2, and HCWS3 were obtained using a dynamic autoclave in specific conditions—temperature of 220 °C, autogenous pressure, 1:10 biomass–water weight ratio—and for three different reaction times, 1 h, 6 h, and 12 h. The HCWSs were characterized by means of ATR-FTIR and SEM-EDS analyses and tested as possible adsorbents to assess the removal efficiencies of some emerging pharmaceutical pollutants (paracetamol and methylene blue) by UV–VIS spectrophotometry. Kinetic and adsorption studies were carried out. The best results were obtained for the HCWS3 hydrochar. Further perspectives include an activation step of the hydrochars and their testing on other emerging pharmaceutical pollutants.