Statistical design of experiments as a tool for optimizing the batch conditions to methylene blue biosorption on yellow passion fruit and mandarin peels

In order to reduce the total number of experiments for achieving the highest removal of methylene blue (MB) from aqueous solutions using yellow passion fruit peel (Passiflora edullis, F. flavicarpa) and mandarin peel (Citrus reticulata) as biosorbents two independent sets of full 23 factorial designs with two central points (10 experiments) were experimented. In order to continue the optimization of the system a new full 22 factorial design with two central points (six experiments) and a central composite surface analysis (13 experiments, divided into four cube points, five centre points, and four axial points) were employed for yellow passion fruit peel (PFP) and mandarin peel (MP), respectively. Using these statistical tools, the best conditions for MB removal from aqueous solution were initial methylene blue (C0) of 3.20 mg l−1, pH 9.0 for PFP and 11.0 for MP and time of contact higher than 48 h for PFP and 42.9 h for MP.