Optimization of Ultrasonication for Chlorella sp. Growth: Impacts on Biomass Productivity and Nutrient Utilization

Aims: This study aimed to investigate the effect of ultrasonic treatment of different durations on Chlorella sp. culture to analyze biomass concentration, biomass productivity and chlorophyll and macronutrients, such as nitrate and phosphate, which were added to the Chlorella sp. culture.

Study Design: This investigation sought to optimize the duration of exposure of live microalgal culture to ultrasonic treatment to estimate economically significant biomass and pigments. Microalgal biomass has potential applications in biofuels, pharmaceuticals, and nutraceuticals, and is highly sought after by industry. Consequently, it is imperative to optimize this process for large-scale production. Chlorophyll pigment is not only crucial in the photosynthesis process but also serves as a high-value component in the food, cosmetic, and health industries. Furthermore, utilizing the optimized duration of ultrasonication treatment, residual nitrate and phosphate in the medium were analyzed, providing key insights into the nutrient consumption of Chlorella sp. under ultrasonication stress.

Place and Duration of Study: The present investigation was conducted over 36 days to estimate the effect of ultrasonication on biomass, chlorophyll, nitrate and phosphorus concentration in Chlorella culture at the laboratory of Synthetic Ecology and Environment Biotechnology, Department of Environmental Science, School of Earth Sciences, Central University of Rajasthan, Bandarsindri, Ajmer.

Methodology: In this study, the effects of ultrasonication on biomass and chlorophyll content were evaluated by treating Chlorella sp. cultures for 5, 10, and 15 min in addition to an untreated control group. Based on these results, an optimized ultrasonication duration of 5 min was selected for further analysis. During this phase, the nitrate and phosphorus contents in the culture medium were measured to investigate the influence of ultrasonication on these nutrient levels. All treatments were conducted in triplicate to ensure reproducibility of the results, with the mean and standard deviation calculated as measures of statistical reliability. The use of mean and standard deviation in triplicate tests ensure that the results are consistent and reproducible, hence providing a measure of statistical dependability.

Results: The biomass concentration and biomass productivity concentration increased from 29.9 ± 0.00240 mg/L (control) to 66.8 ± 0.01485 mg/L, 1.275 ± 0.5033 (control) to 3.71 ± 0.4163 mg/L/day respectively. The highest total chlorophyll concentration was observed in the exponential phase (9 days of culture) which was 3.7772 ± 0.0500. There was a decrease in the concentrations of nitrate and phosphate throughout the culture period, with a total nitrate consumption of 38.5% and total phosphate consumption of 24%.

Conclusion: Chlorophyll and biomass concentrations were maximized after 5 min of ultrasonic treatment, but declined with longer exposure. Nutrient analysis revealed a significant decrease in nitrate and phosphate concentrations over time, consistent with nutrient uptake by the growing cells and the subsequent accumulation of metabolites.