Removal of Sulfamethoxazole by Adsorption and Biodegradation in the Subsurface: Batch and Column Experiments with Soil and Biochar Amendments

Yao, Wenwen

Etd

Removal of Sulfamethoxazole by Adsorption and Biodegradation in the Subsurface: Batch and Column Experiments with Soil and Biochar Amendments

Public

The wide use and the incomplete metabolism of antibiotics, along with the poor removal efficiency of current treatment systems, results in the introduction of large quantities of antibiotics to the environment through the discharge of treated and untreated wastewater. If not treated or attenuated near the source of discharge, the antibiotics can be distributed widely in the environment. In this research, sulfamethoxazole (SMX), a common sulfonamide antibiotic, was selected as a model compound due to its presence in the environment and its resistance to remediation and natural attenuation. Among the various entry routes, discharges from on-site disposal systems are of particular interest due to the wide use of these systems. The complex nature of subsurface transport downstream of these systems adds difficulties to the removal of SMX from subsurface discharges. For this research, two processes that impact SMX removal, biodegradation and sorption, were examined to determine the primary factors governing the elimination of SMX from septic effluent discharges in the subsurface. To characterize the biodegradation of SMX, batch experiments were conducted with SMX in the presence of septic effluent and soil for both aerobic and anoxic conditions. Results showed that SMX removal was limited in the septic effluent but increased in the presence of soil, demonstrating the important role of the soil in SMX removal in both aerobic and anoxic conditions. Addition of external nutrients (ammonium and sulfate) had small effects on SMX removal, although SMX removal was enhanced under aerobic condition with increased dissolved organic carbon. To overcome the limited sorption of SMX on soil, soil amendments were developed and evaluated using biochar, a green and cost-effective adsorbent. Biochars produced from different types of feedstock were characterized for different pyrolysis temperatures, and their adsorption behaviors were examined and compared with commercial biochar and activated carbon (AC). Adsorption isotherms were developed and adsorption kinetics of soil, biochar and AC were studied. Results showed that adsorption on soil, biochar and AC followed three different kinetics models and their equilibrium isotherms followed the Freunlich model. Higher adsorption rates were achieved with biochars prepared at the higher temperature. A lab-engineered biochar with pine sawdust at 500 °C achieved comparable sorption capacity to AC. SMX transport in subsurface was also explored with saturated soil columns filled with soil that was mixed with biochar at different percentages. Significant SMX removal (including complete elimination at a low flowrate and over 90 % elimination at a high flowrate) for all cases was primarily attributed to biodegradation. These results provide insight into the transport and transformations affecting SMX, and then provide a basis for developing low-cost approaches for the mitigation of SMX.

Creator