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Authors: Osrunwense, J.O.,
Aluyor, E.O.
Ekhaise, F.O
Audu, T.O.K
Keywords: Toxic substance
ion exchange
Issue Date: 2014
Publisher: Australia Journal of Engineering Research
Series/Report no.: 38 - 51.;
Abstract: Biodiesel is a renewable fuel developed as a promising alternative to petroleum diesel. It can be produced by converting the triglycerides in vegetable oils and animals fats via several approaches such as alcoholic trans-esterification using alkali or acid catalysis; enzymes, supercritical methanol, ultrasonic traditional and thermal decomposition of oil to form fatty acid alkyl ester (FAAE). All waste products generated from the production of biodiesel are toxic. While most researchers engaged in the development of the technical aspect of biodiesel production, the environmental impact and management of the waste products have been neglected. This paper therefore, provides an overview of the different methods of purifying crude biodiesel to ascertain as clean fuel that meets with the emission reeducation targets of the European Standards (EN 14214) and American Society for Testing and Materials (ASTM D675), and the various treatment processes of the waste products. The quantity and nature of the waste products generated from the crude biodiesel depends on the type of feedstock, production processes and the methods of purification adopted. The crude biodiesel, after transesterification using a short chain alcohol is a multi-component mixture containing mainly FAME, methanol, glycerol, salts un-reacted fats and fatty acids, catalysis and other toxic substances from the feedstock types. Residual impurities in an unrefined biodiesel are dangerous to engines and the negative effects on engines include low oxidation stability, corrosion, high viscosity, filter blockage and emission of noxious substances. Various methods of purification have been studied ranging from water washing, membrane separation technology and ion exchange/adsorption processes. Though the most effective and prominently used method is water washing because it is economical and majority of the impurities associated with biodiesel are highly soluble in water, the process produces large volume of highly polluting waste water. Various methods of treating biodiesel wastewater have been reported, the methods are characterized by one disadvantage or another. These include chemical/electrochemical coagulation which generates metal hydroxide in the solution thereby further polluting the wastewater, dissolved air floatation (DAF) suitable only for the separation of oil and grease, advance oxidation process (AOP) leads to formation of intermediate compounds in the wastewater, biological methods have been reported inadequate because the composition of the wastewater is not suitable for microbial growth and combined/intergraded treatment process, too cumbersome and expensive. However, integrated methods of treatment comprising physical, chemical and biological process would be adequate for a single run.
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