Effect of Fed-batch Culturing on the Growth and Lipid Production of Chlorella vulgaris fo. tertia Applying pH-auxostat Acetic Acid and Predefined Exponential Glucose Feeding
The techniques of heterotrophic microalgae cultivation used to be resulting in higher productivity and better yield than autotrophic culturing. Batch cultivation strategy is commonly used with high glucose concentration, but its potential is limited for biomass production at an industrial scale. Usually, the best productivity can obtain at lower glucose concentration. Moreover, other carbon sources can cause inhibition at higher concentrations. Therefore, the fed-batch cultivation strategy is an obvious choice, as it can maintain the optimal amount of carbon source can be maintained throughout the fermentation by automating the feeding. Such self-regulatory automation is provided by the pH-auxostat addition of acetic acid, which was investigated in this study for Chlorella vulgaris fo. tertia. The pH-auxostat fermentation was upscaled, then the feeding profile was modelled and transformed to another fermentation where glucose was used as a carbon source instead of acetic acid. Thus, the preferred carbon sources were compared under the same circumstances. It was found that the tested strain consumes dissolved oxygen very fast on both carbon substrates. It favored the acetic acid at high nitrogen and phosphorus concentrations. The final biomass concentration was 29.2 g/L under pH-auxostat fed-batch strategy with acetic acid and 18.8 g/L with glucose, respectively. The highest lipid content (393 mg/g) was measured from the biomass in the case of acetic acid. The fermentation settings need further optimization, but the results concluded that pH-auxostat acetic acid feeding has a great potential for scale-up of Chlorella fermentation.