Adsorptive coagulation-flocculation removal of antibiotics in sewage treatment plants

Abstract

The persistent existence of antibiotics in sewage wastewater treatment plants in recent years has emerged as a serious issue. This scenario has indicated that coagulation-flocculation process is ineffective in removing antibiotics from sewage. Therefore, adsorptive coagulation-flocculation process has been proposed as novel sewage treatment method to remove antibiotics. In this study, three types of natural zeolites (NZ01, NZ02 and NZ03) from different sources were employed as adsorbents in batch adsorption test to remove selected antibiotics which were tetracycline (TC) and oxytetracycline (OTC). The physical appearance and chemical properties of these natural zeolites were characterized using scanning electron microscopy (SEM), cation exchange capacity (CEC), Brunauer Emmett Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods. Adsorption test was carried out in batch whereas adsorptive coagulation-flocculation was performed using jar test method. The adsorption data was evaluated in terms of equilibrium and kinetic adsorption mechanism. Important parameters including pH of solution, dosage of adsorbents, temperature, initial concentration of antibiotics and contact time were varied to study the effects of these parameters. It has been observed that at pH between 7 to 8, and temperature of 30 °C the adsorption of antibiotics was optimum with about 90% removal of TC and 70% removal of OTC at the dosage of 6 mg/ml of NZ02. In addition, the adsorption of TC and OTC has been proven to follow Elovich kinetic model and Langmuir model for TC and Temkin isotherm model for OTC. The optimum parameters were later applied in adsorptive coagulation-flocculation (ACF) process to remove antibiotics in synthetic wastewater. Langmuir model and pseudosecond order model turned out to be the most suitable isotherm model and kinetics model to represent the adsorption of antibiotics via ACF. The percentage of removal of antibiotics from synthetic wastewater using only alum was clearly proven to be ineffective (about 5%). However, by injecting NZ02 simultaneously, it increased dramatically (about 20-35%). Last but not least, the hybrid process managed to remove 60% of TC and 40% of OTC from sewage wastewater. In conclusion, adsorptive coagulation-flocculation has the potential to be one of the best alternative methods to isolate antibiotics in sewage treatment plants in the most environmentally and economically friendly way.