Biosorption of phenol by modified dead leaves of Posidonia oceanica immobilized in calcium alginate beads: Optimal experimental parameters using central composite design

This study reports the biosorption of phenol using dead leaves of Posidonia oceanica (PO), an endemic seagrass in the Mediterranean Sea. The PO dead leaves were pre-treated with sulfuric acid and carbonized at 500 degrees C for 2 h to increase their adsorptive capacity. Leaves were then immobilized in calcium alginate beads to address problems that arise when free particulate biosorbents are used. Response surface methodology (RSM) based on central composite design (CCD) was carried out to optimize key variables, viz., initial phenol concentration (100-500 mg/L), biosorbent dosage (0.05-0.1 g/50 ml), and alginate beads to solution ratio (1/10-2/10). The effect of the operating variables on phenol biosorption capacity was studied in a batch system and a mathematical model showing the influence of each variable and their interactions was obtained. The predicted second-order quadratic model for the response variable was significant (p < 0.01). Further, an adjusted squared correlation coefficient, R-2 (adj) of 97.7% indicated a satisfactory fit of the model. The results of CCD showed maximum biosorption capacity of about 127 mg/g at 500 mg/L initial phenol concentration, 1 g/L biosorbent dosage, and at 1.85/10 composite beads to solution ratio. This work demonstrates the suitability of using PO dead leaves as an effective low-cost biosorbent for the removal of phenol.