Abstract
Used kitchen oil represents a feasible and renewable biomass to produce green biofuels such as biodiesel. Biodiesel production generates large amounts of by-products such as the crude glycerol fraction, which can be further used biotechnologically as a valuable nutrient for many microorganisms. In this study, we transesterified used kitchen oil with methanol and sodium hydroxide in order to obtain biodiesel and crude glycerol fractions. The crude glycerol fraction consisting of 30% glycerol was integrated into a bioreactor cultivation process as a nutrient source for the growth of Candida zeylanoides ATCC 20367. Cell viability and biomass production were similar to those obtained with batch cultivations on pure glycerol or glucose as the main nutrient substrates. However, the biosynthesis of organic acids (e.g., citric and succinic) was significantly different compared to pure glycerol and glucose used as main carbon sources.
Highlights
Green biofuels have gained the attention of researchers in the last decades, because of the imminent exhaustion of the fossil fuels, and due to the renewable biomass’ potential to be converted into bio-combustibles with high efficiency [1,2]
Biomass is presented as a renewable resource for bioenergy and biochemical production [9,10]. It mostly consists of wood wastes, agricultural crops and their waste derivatives, municipal solid wastes, animal wastes, and residues deriving from food and aquatic plant processing industries; all these can be sources of biogenic and renewable biomaterials and biofuels [9,11,12,13,14,15,16]
Before the addition to fermentation medium, Microorganisms 2019, 7, 265 the pH of the crude glycerol fraction was adjusted to 7 by adding a few drops of 2M HCl, and it was measured with a laboratory pH meter, model InoLab
Summary
Green biofuels have gained the attention of researchers in the last decades, because of the imminent exhaustion of the fossil fuels, and due to the renewable biomass’ potential to be converted into bio-combustibles with high efficiency [1,2]. Biomass is presented as a renewable resource for bioenergy and biochemical production [9,10] It mostly consists of wood wastes, agricultural crops and their waste derivatives, municipal solid wastes, animal wastes, and residues deriving from food and aquatic plant processing industries; all these can be sources of biogenic and renewable biomaterials and biofuels [9,11,12,13,14,15,16]. From the economical point of view, recycled oils and greases resulting from the food sector represent a feasible alternative source of renewable biomass for the biodiesel industry [9,17]. Reusing the used kitchen oils via biotechnological processes with the purpose of producing biofuels, biomaterials, and biochemicals is a step forward in the reduction of environmental pollution caused by their random discharge [19]. Using recycled kitchen oils in the biofuels industry as feedstock material instead of edible oils (e.g., canola, soybean, sunflower, palm oils) might avoid the competition between the exploitation of lands for food versus energy [19,20,21,22]
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