Continuous bioethanol production by the fermentation of food processing waste

The necessity to reduce CO2 emissions and oil consumption has been determining a strong interest in bio-energy and bio-fuels in recent years. The most promising of these biobased fuels is bioethanol , which can be used with a clean combustion, has a high octane number (103), is chemically stable, no toxic and biodegradable. Further, it can be used for vehicles transport as a mixture with oil or pure; in fact, as mixture does not require specific changes on the engine, while when used pure only small changes are requested. Finally, the CO2 emission produced by the bio-ethanol combustion is “environmental friendly”, because deriving from renewable energy sources. So many countries have set up polices to promote development and use of liquid biofuels. The production of bioethanol is performed on a commercial basis by two technological roadmaps, using directly fermentable sweet feedstocks, such as sugarcane and sugar beets, or starchy feedstocks, such as corn and wheat. Of the 51 billion liters of bioethanol produced in 2006, the U.S. production based on corn and the Brazilian production based on sugarcane accounted for 70% of total production. Cellulose materials represent the most abundant global source of biomass and have been largely unutilized. The main problems to develop viable ligneocellulose-to-ethanol bioconversion processes are the lack of organisms capable of fermenting pentose sugars with a acceptable kinetic rate and the energy (and costs) required for breaking the lignocellulosic material structure. Lignocellulosic ethanol is not at large scale production as corn ethanol and sugarcane ethanol. Ethanol can be produced from lignocellulosic materials in various ways; all processes comprise the same main components: hydrolysis of the hemicellulose and the cellulose to monomer sugars, fermentation and product recovery and concentration by distillation. Another important option for the production of bio-ethanol is the use of bio-waste rich in sugars or starchy materials. Has been reported that various BMSW fractions have a vast potential for the production of sugars that eventually can be used for producing bio-ethanol. Moreover conversion of MSW to bio-ethanol can be an alternative sustainable approach to disposal of waste and reduction of the biodegradable fraction of MSW to landfill. These materials are produced in large amount in Europe and can be considered an important feedstock for bio-fuels production: the generation of food-processing waste has been estimated in 222 millions tonnes per year, vegetable and fruit being at 140 million of tonnes/year. In this thesis has been the study of the continuous fermentation process under no-sterile condition of a residue obtained from the marmalade production, with the aim of bio-ethanol fuel production. The fermentations was conducted with a Saccharomyces cerevisiae strain (EC1118) alcoholic tolerant It has been studied both the single CSTR and CSTR with biomass recycling in order to understand the process kinetics and the problems connected with the principal intensification processes utilized in ethanol fermentation. From the different mass balances conducted on the first, second and third part of this work it appears clear that is possible to work under no-sterile conditions in CSTR, and CSTR with biomass recycling obtaining high ethanol/sugars utilized ratio utilizing appropriate solid retention time and hydraulic retention time. The process nevertheless appears, from the kinetic modelling and energy balance, to not be competitive.