Acid Pretreatment of Two Phase Olive Mill Waste to Improve Bioavailable Sugars: Conditions Optimization Using Response Surface Methodology

Abstract

Two phase olive mill waste (TPOMW) is the semisolid waste generated for olive oil production. The organic fraction of this waste includes compounds that serve as a source of carbon and other nutrients for microorganisms, a feature that makes it potentially attractive for bioethanol production. To increase the bioavailability of cellulose and hemicellulose, no soluble carbohydrates, the application of pretreatments is required. This paper presents the results of the optimization of the sulfuric acid pretreatment variables of TPOMW applied to improve sugars bioavailability, using the response surface methodology. First, the Plackett–Burman method was applied to find the relevant variables of the process, using total sugars content as response variable. The results showed that temperature, acid concentration and solid:liquid ratio are significant for this process. Subsequently, these variables were optimized to maximize total sugars content, using the Box–Behnken method, an experimental array based on an incomplete three-level factorial design. The results indicate that the optimum working conditions were 10.10 % w/w for H2SO4 concentration, 95.2 °C for temperature, and 0.17 g dry solid TPOMW per ml of acid solution, obtaining 67 % of sugars content increase.