## 1 Introduction  
Oleaginous microorganisms, including several yeast species, have been known to synthesize high amounts of lipids (20-70% \(w/w\) of their cell dry weight) in their cellular compartments [1, 2]. These intracellular lipids are also referred to as single cell oil (SCO), which can have different FA composition depending on the type of microorganism and the cultivation conditions that are used. The potential of certain yeast species as prominent producers of SCO has received a lot of attention for many years. The reason for that is the promising applications of SCOs in the biofuel and biochemical industries [3]. Currently, there is a global need to reduce the world's dependence on fossil fuels, and to meet the production goals for this high demand, we need to find alternative sources of oil to replace the use of vegetable oils and animal fats as the main resources for biodiesel [4]. To this end, the use of oleaginous yeasts as SCO producers has many advantages, as it does not compete with the feed and food industry, is not susceptible to climate conditions, and does not require arable land [5, 6]. Additionally, the cultivation conditions can be modified, or the yeasts can be genetically engineered to optimize the SCO composition for the targeted applications [7, 8]. The reason for the diversity of the SCO applications lies in their varied fatty acid composition [9]. For instance, when aiming for biodiesel, it has been observed that SCOs have many similarities with vegetable oils [10]. Depending on the fatty acid composition of SCOs, the produced biodiesel can have significantly different properties [8; 11; 12]. As an example, high amounts of saturated fatty acids (SFAs) favor a high cetane number (CN) value, which is related to the ignition quality of the biodiesel and better oxidation stability (OS) which results in longer shelf-life and lower NO\({}_{x}\) emissions. Furthermore, when short-chain SFAs are abundant, the long-chain saturated fatty acids (LCSF) are lower and so are the kinematic viscosity (KN) and the cold filter plugging point (CFPP) [11; 13; 14]. On the other hand, high levels of unsaturated fatty acids are related to low OS, but they improve the low-temperature performance [13; 15; 16]. Thus, a good balance between the different types of fatty acids is required to obtain good physicochemical properties of biodiesel [17]. Monounsaturated fatty acids (MUFAs) have been reported to successfully maintain that balance, therefore FAMEs with high MUFA content are beneficial for good OS and low-temperature properties [10]. However, the obtained SCO does not always contain the ideal combination of fatty acids and it remains challenging to produce biodiesel with the optimal properties. Therefore, more studies are needed to elucidate the effect of the fatty acid composition of SCO on the production of biodiesel, especially since there is a knowledge gap regarding the exploration of candidate oleaginous yeast species grown under different cultivation conditions. The goal of most studies has been the optimization of the cultivation aimed at an economically viable and environmentally friendly SCO production [8]. Therefore, the need to find cost-competitive carbon sources that can be used as sustainable substrates is of high importance [18]. The use of renewable sugar-based substrates, like glucose-containing hydrolysates that are derived from lignocellulosic materials such as residual agricultural and forest biomass or municipal solid wastes, has been investigated [10]. However, to obtain a pure sugar stream from lignocellulosic substrates, a pretreatment followed by saccharification is usually needed, due to the rigid structure of lignocellulosic [19]. These extra steps account for an additional cost in the process. Another approach is to employ anaerobic digestion (AD), which is a more cost-effective method compared to enzymatic hydrolysis, to convert organic waste to bioenergy [20].