Adsorption of sulfamethoxazole on biochar and its impact on reclaimed water irrigation.

Reclaimed water irrigation can satisfy increasing water demand, but it may also introduce pharmaceutical contaminants into the soil and groundwater environment. In this work, a range of laboratory experiments were conducted to test whether biochar can be amended in soils to enhance removal of sulfamethoxazole (SMX) from reclaimed water. Eight types of biochar were tested in laboratory sorption experiments yielding solid-water distribution coefficients (K(d)) of 2-104 L/kg. Two types of biochar with relatively high K(d) were used in column leaching experiments to assess their effect on reclaimed water SMX transport through soils. Only about 2-14% of the SMX was transported through biochar-amended soils, while 60% was found in the leachate of the unamended soils. Toxicity characteristic leaching experiments confirmed that the mobility and bioavailability of SMX in biochar-amended soils were lower than that of unamended soils. However, biochar with high accumulations of SMX was still found to inhibit the growth of the bacteria compared to biochar with less SMX which showed no effects. Thus, biochar with very high pharmaceutical sorption abilities may find use as a low-cost alternative sorbent for treating wastewater plant effluent, but should be used with caution as an amendment to soils irrigated with reclaimed water or waste water.