Improved transesterification conditions for production of clean fuel from municipal wastewater microalgae feedstock

Microalgae have great potential to be used as feedstock for biofuel production. Municipal wastewater is an economically appealing culture medium to produce microalgae. Downstream processing of wastewater-adapted microalgae, i.e. transesterification of extracted lipid, needs to be more investigated due to the difference between lipid profile of pure culture microalgae and wastewater-adapted microalgae. Based on quantitative parameters of acidity, acid value, and triglyceride content it was indicated that free fatty acid and triglyceride contents of wastewater-adapted algal lipid were between the two limits i.e pure microalgal lipid and vegetable oil. Optimal transesterification conditions for wastewater-adapted algal lipid were investigated in terms of acid-catalyzed versus alkaline-catalyzed reactions, temperature and reaction time, and the type of catalyst. It was found that acid-catalyzed transesterification at 70 degrees C for 35 h using sulfuric acid as the catalyst is required to achieve the highest percentage of fatty acid methyl esters of 53.9 +/- 9.6% in the end product. This is quite different from reaction conditions recommended for pure microalgal lipid and vegetable oil transesterification. These operating conditions resulted in a dominant fatty acid methyl ester profile of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid in the product that satisfied international standards specified for biodiesel. The results of this study customizes the transesterification reaction conditions for wastewater-adapted algal lipid and is one step forward towards commercial production of clean fuel from microalgae feedstock obtained from wastewater. (C) 2019 Elsevier Ltd. All rights reserved.