Application of bottom ash from cattle manure combustion for removing fluoride and inactivating pathogenic bacteria in wastewater

Abstract

This study addressed the utilization of bottom ash derived from the combustion of cattle manure (BA-CM) for removing fluoride from industrial wastewater and killing gram-negative (E. coli O157:H7 and S. typhimurium) and gram-positive pathogenic bacteria (L. monocytogenes), and it will ensure both the disposal of solid waste and the purification of water. BA-CM had a pore size corresponding to mesopores (2–50 nm) and a fractal dimension (D) of 2.88. The main elements constituting the BA-CM were calcium (Ca) in the form of Ca5(PO4)3(OH) and CaCO3. The Ca released from BA-CM was helpful for removing fluoride via the formation of CaF2. The fluoride adsorption by BA-CM approached equilibrium after 6 h. The fluoride equilibrium adsorption on to BA-CM was well fitted to the Langmuir model and was calculated to have a maximum adsorption capacity of 112.07 mg/g. At pH 3, the adsorption amount of fluoride was 76.33 mg/g, and as the pH increased to 7, fluoride adsorption decreased to 50.74 mg/g. In the pH range of 7–11, the amount of fluoride adsorbed did not decrease and was maintained (50.53 ± 0.22 mg/g). More than 97% fluoride removal could be achieved using 13.33 g/L of BA-CM. BA-CM treatment effectively inactivated pathogens in the contaminated water. The BA-CM treatment for 4 min achieved 3.77 log CFU/mL and 6.56 log CFU/mL reductions in E. coli O157:H7 and S. typhimurium, respectively. L. monocytogenes exhibited higher resistance to BA-CM than the other pathogens tested, and 30 min was required to achieve a reduction of 6.33 log CFU/mL. BA-CM, obtained from the combustion of cattle manure for energy production, can be used as a value-added material for removing fluoride and disinfecting water contaminated with pathogenic bacteria.