The application of response surface methodology and Design-Expert® for analysis of ciprofloxacin removal from aqueous solution using raw rice husk: kinetic and isotherm studies

Abstract

Antibiotics are critical pollutants that have a major threat to human health and have been reported in many water sources worldwide. The present study reports the usage of raw rice husk (RRH) that is capable of adsorbing ciprofloxacin (CPX) from aqueous solution. Response surface methodology (RSM) was applied to optimize the sorption process. Four adsorption variables (pH, Time, initial concentrations and adsorbent dosage) were investig ated and a quadratic model was developed for the CPX removal percentage. The low prediction error of 1.963 indicates the high prognostic ability of RSM. High regression coefficient (R2 = 0.9910) and the predicted (R2 of 0.9521) is in acceptable agreement with the adjusted (R2 of 0.9826); that is, the difference is less than 0.2, which supports the model significance. Batch experiments were also analyzed to understand the process isothermal, thermodynamic and kinetic characteristics. Characterization of RRH was done using scanning electron microscopy and Fourier-transform infrared spectroscopy and point of zero charge. The results showed that the process followed Langmuir isotherm and Elovich kinetics. The thermodynamic coefficients suggested that the adsorption process was endothermic and spontaneous in nature.