Removal of doxycycline hydrochloride from aqueous solution by rice husk ash using response surface methodology and disposability study

The huge demand and consumption of DOX, its incomplete metabolism, and complex behavior in atmosphere are causing a great ecological issue, which needs to be solved. In the present study, the suitability of rice husk ash (RHA) for the greater sorption efficiency of DOX antibiotic was investigated. Furthermore, disposability study of exhausted RHA was performed using solidification technique and leachate had undergone toxicity test to evaluate the DOX encapsulation ability. The central composite design under RSM was employed for the design of experiment and optimization of adsorption parameters. RHA was characterized using various techniques such as XRD, SEM (EDX), FTIR, BET, and zeta potential analysis. The influence of various adsorption parameters, like initial DOX concentration (C-0), RHA dosage (m), incubation-time period (t), and pH were examined on the performance in terms of DOX elimination % (X-1) and adsorptive capacity (mg/g) (X-2). At optimized conditions, the obtained X-1 and X-2 were 98.85% and 17.74 mg/g, respectively. Moreover, the kinetics data suited well to the pseudo-second-order model. Freundlich, Langmuir, and Redlich-Peterson (R-P) isotherm models were applied, out of which Langmuir model best performed under optimized conditions; m = 5 g/L, t = 85.85 min, DOX concentration = 89.73 mg/L, and pH = 6. The bacterial toxicity test of leachate confirmed complete encapsulation of DOX by solidification technique.