## 1 Introduction  
The constant and continuous decrease in non-renewable energy feedstocks and the concomitant rise in the price of crude oil have resulted in the increment of scientific interest concerning the discovery and study of \"renewable\" types of energy sources. Biodiesel (_viz._ alky-esters of fatty acids esterified with low-molecular weight alcohols) and bioethanol are considered as the most important and interesting types of biofuels [1; 2; 3; 4; 5]. The synthesis of the above-mentioned biofuels is connected with the production of concentrated glycerol-containing waters, which are the principal side-products of these processes. Moreover, besides bioethanol production, important quantities of glycerol-containingwater can also be generated as side products in various alcoholic beverages' production facilities; for instance, during the typical ethanol fermentation process, ethanol is separated via distillation. The liquid fraction of the remaining material (the so-called \"thin stillage\") contains _c._ 2% _w/o_ of glycerol [6]. Additionally, liquid waste streams containing relatively elevated levels of glycerol are generated in the various oelectrochemical facilities employing transformations of vegetable or animal fats (i.e., soap-production facilities) [2; 3]. Finally, even larger quantities of glycerol-containing water can be envisaged to be generated into the near future, due to the very high intra-cellular accumulation of glycerol as a storage material (in quantities up to _c._ 85% _w/w_) in several algal species like _Dunaliella_ sp. In some of the above-mentioned cases, quantities of glycerol in water reaching levels up to 7.8 M (equivalent to _c._ 720 g of glycerol per L of water) may be generated [7]. This entire situation has inevitably negatively affected the price of glycerol feedstocks in the market volume, which presents a constant decrease. In 2007, a landmark year for the process of biodiesel production, in several EU countries including but not limited to Germany, concentrated glycerol-containing water derived from the biodiesel manufacture process, was considered as a \"typical industrial waste-water\". Its price was _c._ 0.0 USD/kg (as opposed to pure glycerol which presented a price of _c._ 1.20 USD/kg that year). Thus, crude glycerol was employed only for biogas production [8]. In the years that followed, the situation has been relatively ameliorated by taking into consideration both the price and the processes of the purification of glycerol; especially in countries with an advanced technological and scientific level, the industrial production of biodiesel was accompanied (and is currently accompanied) by the side production of relatively highly purified industrial glycerol feedstocks (e.g., purity of \(\approx\)85-90% _w/w_, sometimes \(>\)90% _w/w_). This feedstock can be used directly as the starting material for the chemical synthesis of epichlorohydrin or it can be used in various pharmaceutical applications after further purification processes are carried out [1; 4]. In any case though, the appearance of glycerol as a side-product in the various agro-food, biofuel and industrial activities mentioned above, is constantly rising. Therefore, the conversion of this low-value compound into several types of biotechnological products currently attracts enormous attention [3; 4; 5; 9; 10]. Wild-type, mutant (i.e., acetate negative ones) and genetically engineered strains of the non-conventional polymorphic yeast _Yarrowia_ (synonyms: _Candidia--Saccharomyces-Endomycopsis) _lipolytica_ have been successfully used in recent years as microbial cell factories, amenable to convert glycerol into a plethora of valuable interesting compounds, including but not limited to microbial oils, organic acids (i.e., citric acid, succinic acid, acetic acid), yeast mass, sugar alcohols (i.e., mannitol, erythritol, arabitol), etc. [3; 10; 11; 12; 13; 14; 15].