Authors
Mohit Dhali, Jashore University of Science and Technology
Shimul Saha, Bangladesh University of Engineering and Technology
With the advancement of urbanization and the growing global economy, the world is accumulating an increasing amount of municipal sludge (MS), a waste material of wastewater treatment plants. According to the U.S. Environmental Protection Agency, approximately 4 million tons of dry sewage sludge were generated in 2023. Most of the waste is typically applied to land (60%), followed by disposal via landfilling (24%) and incineration (14%). A more sustainable approach would be to convert it into a valuable resource or product. The biochar prepared from MS by the pyrolysis and carbonization process is an advanced production method with a lesser environmental impact. However, to be used as value-added materials, the MS-biochar lacks sufficient functional properties. Therefore, the heteroatom doping approach is applied to enhance its physicochemical properties. In the presented work, a series of N- and N, S-doped MS biochar was prepared at pyrolysis temperatures ranging from 500 to 700 °C under a constant N2 flow. The functionalized MS-biochars were used as a co-catalyst in a composite comprising Bismuth Vanadate (BVO) as the principal photocatalyst. The composites were prepared by the ball mill mixing technique. The XRD and XPS analyses of the prepared composites demonstrated the successful incorporation of BVO crystals and functionalized MS biochar. The composites were applied as photocatalysts for the decontamination of ciprofloxacin (CIP) from the aqueous system. Systematic parameter studies, based on response surface methodology (RSM), were conducted. Among the varied parameters, N, S-doped municipal sludge (NS-MS) biochar-BVO, with a 1:5 mass ratio of NS-MS biochar to BVO, was able to degrade 97% of 10 mg/L ciprofloxacin at 100 minutes under 100 W LED illumination. The Tauc plot from UV-DRS and Nyquist plot from EIS measurements help explain the potential enhanced photocatalytic performance observed in the NSMS-BVO material. Additionally, scavenger studies and recyclability assessments were conducted using the best-performing composite to identify the most prominent reactive species for CIP degradation and evaluate its potential applicability. Thus, the presented work will address: (1) a method to incorporate municipal sludge into a valuable composite material and (2) the applicability of the prepared composite as a photocatalyst in potential pharmaceutical decontamination process.
