# Cell Disruption and Hydrolysis of _Microchloropysis salina_ Biomass as a Feedback for Fermentation
## 3 Results and Discussion
### Mechanical Cell Disruption
#### 3.2.2 Bead Beating
(**a**) Stainless steel (5 mm); (**b**) stainless steel (2 mm); (**c**) tungsten carbide (3 mm); (**d**) glass (3.0 mm). Error bars show the standard deviation of duplicate experiments. determined to be more effective for disrupting the dense biomass of _M. salina_. To reduce the energy consumption of the cell disruption process, stainless steel should be preferred over tungsten carbide as a bead material since it allows sufficient disruption of the microalgal cells despite its much lower density. Furthermore, the best-performing beads proved to be the stainless-steel beads with a diameter of 2 mm, achieving the highest disruption efficiency for all biomass concentrations examined. Thus, the results indicate that the optimal bead size to disrupt dense microalgae biomass is around 2 mm. The literature suggests that _Microchloropysis_ species are harder to disrupt than most other microalgae species ([PERSON] et al., 2016; [PERSON] et al., 2017; [PERSON] et al., 2018), and high bead material densities are more effective on microalgal cell disruption by bead milling ([PERSON] et al., 2017; [PERSON] et al., 2018). For instance, [PERSON] et al. (2017) used the same setup as [PERSON] et al. (2018) for the mechanical disruption of _Microchloropysis_ species, with the only difference being the bead material, namely zirconium oxide instead of glass. This resulted in an increase of disruption efficiency by 40% compared to that reported by [PERSON] et al. after one single pass. For _Microchloropysis_ biomass with 1% solids content, [PERSON] et al. (2017) achieved 76-93% cell disruption after milling with zirconium oxide beads (0.4 mm) for 40 min. [PERSON] et al. (2019) reported 85% cell disruption for _Microchloropysis_ species biomass with 15% solids after milling with zirconium oxide beads (0.8-1.0 mm) for 40 min. In this study, disruption efficiency achieved using the same bead size and material after the same milling duration was much lower. However, it must be noted that these studies used agitator bead mills (0.6-1.0 L grinding chamber), while in the current study, a mixer mill (20 mL grinding jars) was used, which is known to be less efficient than agitator mills ([PERSON] et al., 2018). Optimal bead size depends on agitator design and mill geometry and might vary for different bead mills ([PERSON] et al., 2018). In this study, the highest degree of disruption recorded for _M. salina_ biomass with 10% solids was 97%, using 2 mm steel beads after 40 min of treatment. This corresponds to a theoretical maximum of 25.2 g L\({}^{-1}\) final sugar concentration in the biomass hydrolysate, assuming that the sugar concentration achieved was proportional to the degree of cell disruption and 26% (\(w/w\)) carbohydrate fraction in the dry biomass. Even though increasing the initial solids content of the biomass to 20% would decrease the cell disruption efficiency to 87%, it would also increase the theoretical maximum sugar concentration of the hydrolysate to 45.2 g L\({}^{-1}\), which could be a better option considering the main objective of this work.