A sustainable approach to valorize potato peel waste towards biofuel production

In recent years, humanity has been called upon to redefine how it draws its energy reserves, as well as how to manage and regulate the final disposal of its waste into the environment. Biofuels are considered promising alternatives to fossil fuels. Especially, the second- and third-generation biofuels which are generated from agro-industrial waste can minimize the total disposal of residues, while they contribute to the renewable energy total supply. The current work focuses on the sustainable utilization of potato peel waste (PPW) as a viable raw material in a biorefinery, aiming to produce bioethanol and biogas. Setting dehydration as a necessary pretreatment step, the kinetics and the VFA (volatile fatty acid) production during drying of PPW were also studied. The best results in terms of bioethanol production (71.37 +/- 2.47%) were reached when a chemical pretreatment step (NaOH 1% w/v) was included, followed by enzymatic hydrolysis with two different non-commercial enzymes, an amylolytic (NS22109, 50 mu L/g(starch)) and a cellulolytic (NS22177, 300 mu L/g(cellulose)) enzyme, and alcoholic fermentation with Saccharomyces cerevisiae (2% w/w(dry PPW)). As far as the integration of the processes is concerned, two different scenarios were investigated. The first included anaerobic digestion as a stand-alone procedure for the utilization of PPW and the second included ethanol production and subsequent valorization of stillage via anaerobic digestion. The latter proved as the best scenario for both the energy production and the solid residue degradation providing 7.15*10(3) MJ and 390 kg of fertilizer per ton of dry PPW.