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УДК 502
BIOENERGY AND BIOPRODUCTS FROM AGRO-WASTES AND
WASTEWATER, SOME POTENTIAL PROCESSES
Deiana A®.
Politecnico di Torino, E-mail: sempredeiana@gmail.com
Bachelor degree in Environmental Engineering, Deiana, Andrea
The following article shows some potential solutions for the valorization of wastes and wastewater produced by farms and food industries. It moreover introduces the need of green energy to reduce dependency on fossil fuels.
Keywords: anaerobic digestion, dark fermentation, ABE fermentation.
Due to climatic diversities, farming by-products are different in each region of Europe. Interesting wastes from this sector are principally scrap from cereal crops and manure from different livestock. For what regards food industries, three productions are relevant for the characteristics of their scraps: olive oil mills, sugar industries, cheese industries and wine industries.
® Deiana A., 2016
These agro-industrial wastes are characterised by a big amount of organic compounds for which treatments are required before being able to give them back to nature without causing damage. Some processes have been proved to solve this problem while yielding substances that can be used to produce energy and other products.
The first and most well-known example is the anaerobic digestion in which Biogas can be produced from a variety of substrates, such as energy crops, animal manure, municipal solid waste, sewage sludge, industrial waste, and so on. This product is one of the most efficient and effective option among the various alternative sources of renewable energy currently available. The process consists on the degradation of organic matter by particular microorganisms that work without oxygen. The biological activity is possible between -5 and +70 degrees Celsius, and it is divided in hydrolysis, acidogenesis, acetogenesis and methanogenesis. In these steps, complex substrates are broken down finally producing a mix of 50-80% of CH4, 40-20% of CO2 and other compounds in little percentage, like ammonia, water vapour and so on, that can be used as fuel. Another product of anaerobic digestion is a nutrient-rich digestate that can be used as fertilizer. The process can be classified by temperature and quantity of dry substance. The classic and consolidated one is the wet process, with less than 10% of dry substance, during which every type of stable residual organic biomass can be used combined with wastewater of food industries and sewage sludge. The type of substrate determines the methane yield. Future research is thus concentrating on the best mix of substances in order to maximise biogas yield. Important results have been obtained by grape pomace, wine lees, stalk and wastewater from wine industry. Co-digestion of milk whey, olive pomace and olive mill wastewater has produced a big methane yield. Also co-digestion of organic waste from civil waste sorting and sewage sludge has given good results.
Another important process to convert wastes in bioenergy, is dark fermentation. This consists in the breakdown of carbohydrates that are in the organic substance producing hydrogen, carbon dioxide and fermentation's by-products like organic acids and alcohols. This digestion is possible through microorganisms that obtain energy in glycolysis process, working in anaerobic condition and without light. The last characteristic makes dark fermentation easier and cheaper to realize. A large number of biomass can be used as substrate with the only fundamental requisite of a large amount of carbohydrates. Important results in hydrogen yield have been obtained using molasses and milk whey as substrate. The importance of this process is principally the possibility to produce the best fuel possible,
hydrogen, from wastes and cheap scraps of organic matter, making research in this field really interesting.
Another interesting process for production biofuels and bioproducts, is Acetone-butanol-ethanol (ABE) fermentation that uses bacteria fermentation in order to produce solvents from carbohydrates like starch and glucose also from cellulose biomass (after a transformation, through enzymes, of lignin, cellulose and hemicellulose in sugars). Microorganisms of Clostridia's class produce three parts of acetone, six parts of butanol and one part of ethanol through two steps (acidogenesis and solventogenesis) where bacteria's activity change from synthesis of new biomass to production of solvents, due to decreasing of pH. Substrate for ABE fermentation must be characterized by a large amount of simple sugars, like ligno-cellulosic scraps, straw, molasses, sugar beet cossettes and so on. This process is being given particular attention because it can be a cheaper and no-oil way to produce these important solvents that can be used as raw materials for chemicals like polymers or even as fuels. Butanol could especially represent the future of energy with low impacts for the environment because it has a heat of combustion similar to gasoline's one and it is also less corrosive than ethanol.
These processes can be a relevant solution to oil dependency and waste treatment, reducing impacts of energy production by conventional fuels, and giving an alternative for diversification of energy and chemicals market. Another important aspect is that these technologies must be close to farms and local realities and this can also solve social problems with occupation and wealth.
БИОЭНЕРГИЯ И БИОПРОДУКТЫ ОТ АГРО-ОТХОДОВ И СТОЧНЫХ ВОД, НЕКОТОРЫХ ПРОЦЕССОВ А. Deiana
Политехнический университет Турина, г.Турин, Италия, электронная почта: sempredeiana@gmail.com
В статье приведены некоторые возможные решения для валоризации отходов и сточных вод производства ферм и производств продуктов питания, и необходимость экологически чистой энергии, чтобы уменьшить зависимость ископаемого топлива.
Ключевые слова: анаэробное сбраживание, ферментация темная, Ацетоно-бутиловое брожение.
