## 4 Discussion
### Application Prospects of Electrical Stimulation in Practical Production  
_N. closterium_ f. _minutissima_ is widely used in aquaculture, and establishing an optimized cultivation system can enhance feed production efficiency and nutritional value, thereby promoting the development of the aquaculture industry. This chapter presents electrical stimulation experiments conducted in a workshop photobioreactor to explore the potential application and ecological effects of electrical stimulation in practical production settings. Overall, appropriate electrical stimulation has shown promising results in promoting microalgal growth within photobioreactor systems and holds significant potential. The ecological significance of electrical stimulation primarily includes the following: (1) enhancing microalgal growth and biomass accumulation, thereby increasing ecosystem productivity; and (2) promoting the consumption of nitrogen and phosphorus, which maintains a favorable growth state for microalgae and stabilizes environmental pH. According to experimental results, under 1 V electrical stimulation, the maximum cell density and biomass dry weight of _N. clostrium f. minutissima_ significantly increased by 9.97% and 5.00%, respectively, compared to the control group, with a 12 h advancement into the stationary phase. This initial practical application in production settings represents a successful achievement. In contrast, under 3 V electrical stimulation, both the maximum cell density and biomass significantly decreased by 20.37% and 9.50%, respectively. These findings corroborate the dual effect of electrical stimulation: it can promote microalgal growth within a certain range but inhibit it at higher voltages. There may be an optimal voltage for promoting microalgal growth between 1 V and 3 V that requires further investigation. Notably, this study selected the optimal voltage of 1 V for promoting cell density and 3 V for nutrient accumulation from the transient stimulation experiment, as well as 0.5 V as the overall optimal voltage from the continuous stimulation experiment. It was found that under modified photobioreactor production conditions, 1 V served as the optimal voltage, while 3 V inhibited microalgal growth, and the effects of 0.5 V were not significant. This indicates that the effects of electrical stimulation can vary under different application scenarios, suggesting that the optimal voltage for promoting microalgal growth is influenced by multiple factors and must be explored in specific contexts and conditions. In laboratory results, notable inflections in growth curves were observed for the D-3 V and D-5 V groups, coupled with high growth rates, likely due to nutrient depletion in the culture medium. To prevent nutrient deficiency from limiting microalgal growth during production applications in the photobioreactor, an additional nutrient feed was introduced after 48 h. The growth curves indicate that this feeding allows microalgae to re-enter the logarithmic phase, achieving higher stationary phase densities, with the 1 V + feeding group reaching a cell density of 12.17 \(\pm\) 0.49 \(\times\) 10\({}^{6}\) cell/mL, significantly surpassing previous limitations, while the 0 V + feeding group also achieved 11.10 \(\pm\) 0.53 \(\times\) 10\({}^{6}\) cell/mL. These findings hold important guidance for optimizing microalgal cultivation in workshop photobioreactors. The pH levels and nitrogen and phosphorus consumption by microalgae within the photobioreactor support the promoting effect of 1 V electrical stimulation on microalgal growth and the inhibitory effect of 3 V stimulation. They also highlight the potential of combining electrical stimulation with marine microalgae for water treatment applications. Recent studies have demonstrated that the combination of microalgae and electrical stimulation has considerable capacity for the removal of nitrogen and phosphorus from the environment, suggesting that bacteria may synergistically contribute to water purification alongside microalgae [21; 31; 34; 35].