Influence of biochar thermal regeneration on sulfamethoxazole and dissolved organic matter adsorption

Biochar is emerging as a cost-effective, environmentally-sustainable adsorbent for removing organic contaminants (OC) from wastewater, stormwater, and drinking water, but strategies for managing exhausted biochar are needed. Here, pine biochar generated at 850 degrees C was exhausted by background dissolved organic matter isolated from surface water [dissolved organic carbon similar to 4.2 mg L-1, UV-absorbance at 254 nm (UVA(254)) similar to 0.10 cm(-1)] and sulfamethoxazole (SMX) [similar to 200 ng L-1], in a column. Exhausted biochar underwent a semi-oxic-thermal-regeneration step at 600 degrees C (i.e., heat treatment). SMX and UVA(254) adsorption capacity and breakthrough were evaluated in rapid small-scale column tests (RSSCTs). Relative to fresh biochar, heat treated biochar that had been exhausted exhibited similar to 3.5-fold and similar to 3-fold greater SMX and UVA(254) adsorption capacities, respectively, and similar to 3-fold increase in adsorption efficiency (i.e., mass loss-adjusted SMX adsorption capacity). When applying the heat treatment to fresh biochar, a similar improvement in adsorption capacity was observed. Adsorption capacity and BET surface area were positively correlated and continued to increase after a second exhaustion-regeneration cycle, but the adsorption efficiency remained the same due to mass loss. SMX breakthrough correlated with that of UVA(254), which provides the basis for a rapid, inexpensive method to predict OC breakthrough. Heat-treated biochar's SMX adsorption capacity was similar to 20% of activated carbon's. Greater empty-bed-contact times increased the SMX adsorption capacity of heat-treated biochar. These results suggest that thermal regeneration could enhance the economic and environmental sustainability of biochar sorbents.