## 3 Results  
### Conversion of Waste Glycerol with Free and Immobilized Cells of G. oxydans ATCC 621  
Time profiles of glycerol conversion and DHA formation during biotransformation of 30 g:L\({}^{-1}\) of a waste glycerol fraction with the use of free or immobilized _G. oxydans_ cells are depicted in Figures 2 and 3. Conversion of the waste fraction of glycerol (initial concentration 30 g:L\({}^{-1}\)) with the use of free cells caused a rapid depletion of substrate concentration by approximately 19 g:L\({}^{-1}\) within 24 h.  
Figure 3: Time profiles of glycerol conversion and DHA formation during biotransformation of 30 g:L\({}^{-1}\) waste glycerol with immobilized _G. oxydans_ cells. Figure 2: Time profiles of glycerol conversion and dihydroxyacetone (DHA) formation during biotransformation of 30 g:L\({}^{-1}\) waste glycerol with free _G. oxydans_ cells. After another day of the process, the substrate concentration decreased to the final value of 0.9 g\(\cdot\)L\({}^{-1}\) (Figure 2). Extending the conversion time to 96 h had no significant effect on glycerol concentration in the reaction medium (Figure 2). In the reaction with free _G. oxydans_ cells and an initial crude glycerol content of 3%, the concentration of DHA was about 9 g\(\cdot\)L\({}^{-1}\) and 18 g\(\cdot\)L\({}^{-1}\) after 24 and 48 h of biotransformation, respectively (Figure 2). The highest concentration of the expected product was observed after 72 h and was approximately 20 g\(\cdot\)L\({}^{-1}\). Elongation of the bioconversion process to 96 h resulted in a decrease in DHA concentration in the reaction media (Figure 2). During conversion of 30 g\(\cdot\)L\({}^{-1}\) of a crude glycerol fraction with immobilized cells as biocatalysts, the glycerol concentration decrease was slower compared with the same reaction conducted using free cells (Figures 2 and 3). The lowest substrate concentration (0.9 g\(\cdot\)L\({}^{-1}\)) was determined after 72 h of the bioconversion process and it was sustained at the same level until the end of the process (Figure 3). In the medium with 3% initial glycerol concentration and immobilized cells, DHA production was lower than in the same medium but with a different biocatalyst (free cells), regardless of process duration. The maximum concentration of the final product reached after 72 h was about 14.6 g\(\cdot\)L\({}^{-1}\) (Figure 3). Time profiles of glycerol conversion and DHA formation during bioconversion of 50 g\(\cdot\)L\({}^{-1}\) of a waste glycerol fraction with free or immobilized _G. oxydans_ cells are presented in Figures 4 and 5. Figure 4: Time profiles of glycerol conversion and DHA formation during conversion of 50 g\(\cdot\)L\({}^{-1}\) of a waste glycerol fraction with free _G. oxydans_ cells. Figure 5: Time profiles of glycerol conversion and DHA formation during conversion of 50 g\(\cdot\)L\({}^{-1}\) of a waste glycerol fraction with immobilized _G. oxydans_ cells. In the medium with 50 g-L\({}^{-1}\) of waste glycerol and free cells, substrate utilization was observed only for the first 48 h of the bioconversion process (Figure 4). Subsequently, the concentration of glycerol remained steady at about 22.5 g-L\({}^{-1}\) (Figure 4). Concurrently, the DHA concentration in the reaction mixture increased to about 9 g-L\({}^{-1}\) (after 24), 19 g-L\({}^{-1}\) (after 48 h), and 21 g-L\({}^{-1}\) at the end of the process (Figure 4). During the first two days of bioconversion with 5% of the initial waste content, glycerol consumption was slower in the medium with the immobilized cells, however at the 72 nd and 96 th hour it's concentration was lower than in the process with free cells (about 3 and 4 g-L\({}^{-1}\) after 72 and 96 h, respectively) (Figures 4 and 5). The highest concentration of the expected product was approximately 16 g-L\({}^{-1}\) after 96 h of the bioconversion process (Figure 5).