Biomass waste

Legend:

Long Chain Fatty Acids (LCFA)

Linoleic Acid (LA)

Arachidonic Acid (ARA)

Eicosapentaenoic acid (EPA)

Docosahexaenoic acid (DHA)

Fish Oil (FO)

Vegetable Oil (VO)

Microbial Oil (MO)

Edible biomasses are not sustainable as substrates for biotechnological use, since their high economic, environmental and social costs are unbearable. For this reason, despite the presence of inhibitory compounds for microbial cell growth, the use of raw materials and by-products is highly desirable.

Glycerol can be considered as a by-product mainly deriving from biodiesel production. Indeed, the triglyceride trans-esterification releases glycerol at the end of the process. It is estimated that for every 100 kg of biodiesel produced, 10 to 11 kg of crude glycerol are generated. Because of the rapid growth of biodiesel industry, a large surplus of glycerol has been generated. This in turn affects the market value: even if the prices are quite volatile, glycerol can be considered as a cheap carbon source, and crude glycerol is even cheaper. An efficient valorization of crude glycerol is difficult to achieve, despite this would help significantly in reducing the costs of the overall biodiesel production. The problematic in using this industrial by-product as such is mainly related to the impurities present therein: residual methanol, sodium hydroxide, some esters and low amounts of proteins and minerals. These contaminants strongly limit crude glycerol application in chemistry or pharmaceuticals without a purification step, which is costly and energy-intensive. However, microbial ability to transform an excess of carbon source into polymeric reservoirs -up to 70% of their dry weight- is well known. For these reasons, the microbial conversion of crude glycerol into value added compounds attracts increasing interest and represents an alternative and environmentally friendly strategy.