# Cell Disruption and Hydrolysis of _Microchloropysis salina_ Biomass as a Feedback for Fermentation
## 3 Results and Discussion
### Mechanical Cell Disruption
#### 3.2.3 High-Pressure Homogenization  
High-pressure homogenization for the disruption of _M. salina_ cells was examined first on a laboratory scale using a bench-top HPH, followed by a scale-up to 200 L using an industrial HPH. On the laboratory scale, microalgal biomass with solids content varying between 10 and 25% was homogenized for up to 10 passes through the HPH. Figure 5 shows the results of cell disruption using the bench-top HPH at two different exit pressures. At a pressure of 1500 bar, for all CDW concentrations, disruption efficiency kept increasing with each pass through the HPH, reaching a final value between 40 and 63% after 10 passes (Figure 5a). At a pressure of 3000 bar, a higher disruption degree between 56 and 78% was achieved for all CDW concentrations after 10 passes (Figure 5b). However, the difference between various solids contents was more apparent at 3000 bar. With 10% solids content, a cell disruption degree of 75% was achieved already after four passes, while this took eight passes with a solids content of 15%. Still, disruption efficiency stayed below 80% in both cases despite further treatment. For biomass with 20-25% solids content, maximum disruption efficiency reached only 56-60%. Figure 6 shows the results of the scale-up experiments to 200 L using an industrial HPH. Microalgal biomass with a solids content of 15% was homogenized with up to five passes at 1000 bar. The degree of cell disruption is plotted with respect to the number of equivalent passes, which is the time equivalent of a single pass when the biomass is circulated in an agitated tank during homogenization. On the 30 L scale, cell disruption efficiency reached 94% after 4.5 equivalent passes. In contrast, on 60 L and 200 L scales, cell disruption efficiency reached around 80% after 2-3 passes and did not increase afterward despite further homogenization. Nevertheless, the industrial HPH was more effective than the bench-top HPH, achieving over 70% cell disruption of biomass with 15% solids after two passes at 1000 bar, whereas this required six passes at 3000 bar with the bench-top HPH (Figures 5b and 6b). In this study, the industrial HPH proved more effective than the bench-top HPH, achieving a higher degree of cell disruption after fewer passes at a lower pressure. This is not surprising since the efficacy of HPH depends highly on the material and design of its  
Figure 5: Disruption of _M. salina_ biomass with HPH on a 200 mL scale. Microalgal biomass with various solids content ranging between 10 and 25%, as indicated by the legend, was homogenized for up to 10 passes. (**a**) Exit pressure of 1500 bar; (**b**) exit pressure of 3000 bar. Error bars show the standard deviation of triplicate experiments. Figure 6: Disruption of _M. salina_ biomass with HPH at 1000 bar exit pressure on 30 L (), 60 L (), and 200 L () scales. Microalgal biomass with a solids content of 15% was homogenized for up to 5 passes. The degree of cell disruption is plotted with respect to the number of equivalent passes (N\({}_{\rm E}\)), which is the time equivalent of a single pass when the biomass is circulated in an agitated tank during homogenization. (**a**) Degree of cell disruption on different scales; (**b**) mean value of disruption degree on different scales. Error bars show the standard deviation between different experiments. mechanical parts, especially of the homogenizing valve [19]. In general, HPH has proved to be an effective method for disrupting _M. salina_ cells, even though the maximum disruption efficiency (86%) achieved with 15% solids content remained below the efficiency recorded for bead milling with 2 mm stainless-steel beads (90%). The literature describes the best method of cell disruption as dependent on the microalgae strain. [PERSON] et al. [42] stated that the most effective mechanical disruption method for _Chlorococcum_ sp. cells is HPH, whereas [PERSON] et al. [43] demonstrated that bead milling was significantly more efficient than HPH for disrupting _Botryococcus braunii_ cells.