David E. Leiva-Candia and M. P. Dorado

Abstract The biodiesel industry is gaining interest in the past years due to the depletion of the easily extracted petroleum, the increasing demand to the automotive market, and the environmental damage. It is acknowledged that the main obstacle to biodiesel marketing is the cost of production, which is mostly due to the price of the raw material (usually vegetable oils). In this way, the goal is to provide low-cost raw materials. This may be achieved by feedstocks that do not require arable land, do not depend on growing seasons, and that give added value to waste, helping also to its recycling. In this way, oleaginous organisms may be considered an alternative feedstock for the biodiesel industry, as they meet all the previous requirements. This chapter presents the state of the art and the main characteristics of the oil and bio­diesel provided by macroorganism (insects) and microorganism (bacteria, filamen­tous fungi, and yeasts).

1 Introduction

It is worldwide accepted that biodiesel is an attractive alternative to fossil diesel fuel in terms of exhaust emissions besides its renewable nature (Demirbas 2009). However, the market inclusion of first-generation biodiesel is controversial due to the “food versus fuel” discussion (Pinzi et al. 2009). Moreover, it is not economi­cally viable in the absence of both tax exemption and high petroleum-derived

D. E. Leiva-Candia • M. P. Dorado (H)

Department of Physical Chemistry and Applied Thermodynamics, University of Cordoba, Cordoba, Spain e-mail: pilar. dorado@uco. es

D. E. Leiva-Candia e-mail: z82lecad@uco. es

A. Domingos Padula et al. (eds.), Liquid Biofuels: Emergence, Development and Prospects, Lecture Notes in Energy 27, DOI: 10.1007/978-1-4471-6482-1_11, © Springer-Verlag London 2014

fuel prices (Janda et al. 2012), as a result of the high cost of the raw materials (60-75 % of the total cost of biodiesel) (Dorado et al. 2006; Gui et al. 2008). In this sense, research is focused on new renewable non-edible low-cost raw materi­als that do not need arable land. Second-generation biodiesel, mainly constituted by non-edible oil, waste oil, and animal fat-based biodiesel, partially complies with the above requirements, as in some cases, it requires land to produce the raw materi­als. Third-generation biodiesel uses non-edible oleaginous alternative sources fully independent of climate or availability of land. Among the possibilities, there is a novel source of raw materials composed by macro — and microorganisms that are able to produce oil.

In the category of macroorganisms, insects show a great potential in terms of fat accumulation, in some cases above 25-30 %, especially during the immature stages (larva, pupa, and nymph) (Manzano-Agugliaro et al. 2012). The fat contents of oleaginous insects vary according to the species and location, being Coleoptera and Lepidoptera species the ones that provide the highest amount of fat (Ramos — Elorduy 2008). Insects have shown a high potential to replace oleaginous seeds as raw material for biodiesel production, due to their high food efficiency, high repro­duction rate, and short life cycle (Li et al. 2012). Furthermore, biodiesel derived from insect oil fulfills both ASTM D6751 and EN 14214 standards (Leung et al. 2012; Li et al. 2012).

Microbial oil or single-cell oil proceeds from different oleaginous microorgan­isms, i. e., bacteria, fungi, and microalgae (Li et al. 2008). These microorganisms are able to accumulate intracellular lipids above 20 % of their dry cell weight. Besides, they do not require arable land and allow the recycling of residual bio­mass, as it can be used as a carbon source (Azocar et al. 2010). The accumu­lation of lipids depends on the kind of microorganism, culture conditions, and the relation C/N, as under nitrogen limitation, the accumulation of oil increases. The oleaginous microorganisms are able to consume a variety of carbon sub­strates following different metabolic pathways (Xu et al. 2013). Currently, tech­nologies for the production of microbial oil are still in pilot scale, i. e., Nestea Oil Company uses waste as medium and expects commercial production after 2015 (Neste oil 2012).

The potential use of microbial oil as a feedstock for the biodiesel industry is surrounded by a great expectation, as oleaginous microorganisms can be grown in conventional microbial bioreactors, improving the biomass yield and reduc­ing the cost of produced biomass and oil (Vicente et al. 2009). For the reasons mentioned above, this chapter includes the main characteristics and properties of microbial oil, with special focus on the use of waste as substrate and the sub­sequent biodiesel. Microalgae have been removed from this chapter as the sole explanation of the cultivation technology requires a fully dedicated chapter.