Optimization, equilibrium, kinetic and thermodynamic studies on adsorptive remediation of phenol onto natural guava leaf powder

Environmental considerations require disposal of the contaminants in a safe manner without causing any harm. Accordingly, the contaminants should be removed and recovered as value or disposed without any burden to the environment. In this context, natural biodegradable adsorbents could possibly be an answer as they get biodegraded along with the organic contaminants including phenol. Having observed from literature that the natural guava leaf powder (NGLP) can be used as an adsorbent, experimental studies were carried out to investigate the potential of NGLP to remove phenol from aqueous solutions. Batch experiments were carried out using NGLP and the effect of different variables such as pH, NGLP dosage, contact time and agitation speed was studied using response surface methodology (RSM) with Box–Behnken approach and the significant parameters were optimized by subsequent experimentation. The optimized parameters obtained in our studies correspond to pH 5.85 for a NGLP dosage of 2.15 g/L, at an agitation speed of 140 rpm and a contact time of 9 h for the initial phenol concentrations ranging from 50 to 250 mg/L. The absorption of phenol onto NGLP was confirmed using FTIR and SEM-EDX. Thermodynamic, kinetic and equilibrium isotherm studies were conducted using the optimal parameters. The adsorption data fitted well with Langmuir isotherm (R²= 0.9982) for the batch equilibrium studies and the pseudo-second-order type model (R²= 0.9743–0.9921) depicted the phenol adsorption kinetics. The maximum adsorption capacity of NGLP for phenol was 10.85 mg/g. The results inferred the feasibility of using NGLP as a phenol adsorbent and Box–Behnken design as an effective tool for the optimization of process conditions. Even though the studies are not intended to reuse the adsorbent in view of abundance and biodegradability, the preliminary experiments have indicated the possible potential of desorption and reusability.