Factorial experimental design for optimizating the removal conditions of lead ions from aqueous solutions by three wastes of the olive-oil production

Abstract

Olive stone (OS), two-phase olive mill solid (OMS) and also olive tree pruning waste (OTP), three wastes of the olive-oil production, were tested as low-cost adsorbents for Pb (II) removal from aqueous solutions. In order to reduce the total number of experiments to achieve the best conditions of the batch biosorption procedure, two 3 2 factorial designs of experiments were carried out for each biosorbent. The factors considered were biosorbent dosage, pH, initial lead concentration and temperature. Three levels for each factor were used; biosorbent dosage (2 g/L; 10 g/L and 22 g/L), pH (4; 5 and 6), initial lead concentration (10 mg/L; 40 mg/L and 70 mg/L) and temperature (25 °C; 40 °C and 60 °C). Two responses, the lead removal percentage and biosorption capacity after 120 min of contact time, were then analyzed statistically using the Statgraphics Plus 5.1 software. A second-order quadratic model suggested the optimum conditions. Three dimensional plots demonstrated relationships between the lead ion uptake with the paired factors, describing the behaviour of biosorption system in a batch process.