Thermal Regeneration of Biochar for Adsorption of Synthetic Organic Contaminants in the Presence of Dissolved Organic Matter

Biochar is emerging as a cost effective carbonaceous adsorbent for removing pollutants such as synthetic organic contaminants (SOCs) from wastewater, stormwater, and drinking water sources. However, relative to commercial activated carbon (AC), biochar fouls rapidly when applied in a flow-through column in the presence of background dissolved organic matter (DOM). Thermal regeneration is a promising process for regaining adsorption capacity in fouled biochar. In this study, 850 °C pine biochar was fouled in a column with environmentally relevant concentrations of sulfamethoxazole (SMX) and DOM, then heated in a second semi-oxic thermal regeneration step at 600 °C. The treatment resulted in a dramatic improvement in SMX column adsorption capacity in the presence of DOM. DOM adsorption capacity was also improved. The treatment was applied to fresh char that had not been fouled, and the improvement in adsorption capacity was still observed. This increase in adsorption capacity was strongly correlated with an observed increase in BET surface area and decrease in average pore diameter, and was still significant even after accounting for the decrease in mass of char during the heating step. The improvement in adsorption capacity and increase in surface area was repeatable for multiple cycles of fouling and regeneration, although the further increase in adsorption capacity in the second regeneration cycle was counteracted by the loss of mass of char. While the adsorption capacity of biochar for SMX in the presence of DOM was greatly improved by the second heating step, it still did not approach the capacity of the activated carbon. A positive effect of empty bed contact time (EBCT) on SMX adsorption capacity was observed for biochar after the regeneration/enhancement heating step, and for activated carbon, but not for fresh biochar. A change in particle size distribution was not observed due to the reheating process