Diluted acid hydrolysis pretreatment of agri-food wastes for bioethanol production

Because of its environmental benefits, bioethanol is regarded as a promising biofuel substitute for gasoline in the transportation sector. To make it competitive with fossil fuels, it is necessary to reduce production costs by using new, alternative biomass feedstocks. As a result of its strong agricultural growth, Spain has seen increased development of its vegetable canning industry which produces approximately 450,000 tonnes of waste a year. Solutions must be developed in order to diminish the environmental impact from this increasing amount of waste.For this study, wastes from fresh and processed vegetables were used as feedstocks for a diluted acid hydrolysis process using sulphuric acid as a catalytic agent.The maximum ratios of single sugar recovery in the liquid fraction from dilute acid hydrolysis assays were 40.29 and 50.20% (w/w) for tomato and red pepper residues, respectively (Table 3). More intensive pretreatment was necessary to maximise sugar recovery in the case of pulse food (legumes such as beans, lentils and chickpeas) and artichoke residues because of their high starch and inulin content. Finally, for cardoon residues a maximum single sugar recovery of 78.18% (w/w) was obtained in the liquid fraction (Table 4). The suitability of these pretreatments has also been evaluated by corroborating the low levels of sugar degradation compounds detected in the samples, which are significantly lower than the concentrations reported in previous studies.In conclusion, because the sugars in fresh and processed vegetable wastes are widely available and easily obtainable, they can be considered as potential feedstocks for bioethanol production.