Monitoring of Algae Growth by TOC Measurement

Importance of the Topic

The global search for sustainable energy sources has highlighted microalgae as a promising biomass fuel. Microalgae can produce high oil yields without competing with food crops and can be cultivated on non-arable land. Monitoring the growth and metabolic state of microalgae is essential to optimize cultivation conditions and maximize biofuel productivity. Total organic carbon (TOC) analysis provides a rapid, direct measure of biomass accumulation and carbon balance during culture, facilitating informed decisions in research and industrial applications.

Study Objectives and Overview

This application example, conducted by the University of Tsukuba Shiraiwa laboratory in collaboration with Shimadzu, demonstrates the use of the Shimadzu TOC-L CPH analyzer to track microalgal growth. The main goals were to measure suspended-cell TOC directly without sample pretreatment, differentiate organic and inorganic carbon fractions, and correlate carbon metrics with biomass indicators over an eight-day culture period.

Methodology

• Microalgae cultivation: Cells were grown in suspension over eight days.
• Sample preparation: Two daily samples were taken—Sample 1 containing cells in suspension and Sample 2 after cell removal by centrifugation.
• TOC determination: TOC was calculated as the difference between total carbon (TC) and inorganic carbon (IC) for each sample.
• Biomass index: Turbidity of Sample 1 served as a proxy for cell mass.
• Data collection: Daily measurements of TC, TOC, IC, and turbidity were recorded to observe growth dynamics.

Instrumentation

• Analyzer: Shimadzu TOC-L CPH combustion-type total organic carbon analyzer.
• Catalyst: Standard platinum catalyst for complete oxidation of organics.
• Calibration: One-point calibration using 1000 mg/L potassium hydrogen phthalate solution.
• Sample volume: 10–20 mL per measurement, sampled under magnetic stirring.

Main Results and Discussion

During the culture period, TC and TOC values associated with the microalgal cells increased in parallel with turbidity, reflecting biomass accumulation. IC also rose but at a lower rate. The TOC/TC ratio peaked mid-cycle, indicating maximum organic carbon incorporation. Later, a slight decline in TOC/TC suggested onset of stationary phase or metabolic shifts. These trends demonstrate that direct TOC monitoring can reveal carbon allocation patterns and physiological status without sample pretreatment.

Benefits and Practical Applications

• Rapid, direct measurement of organic carbon in cell suspensions accelerates process monitoring.
• No filtration or chemical pretreatment simplifies workflow and reduces potential sample alteration.
• Quantitative carbon balance data support optimization of culture conditions and scale-up strategies.
• Small sample volume requirements make the method suitable for laboratory-scale experiments.

Future Trends and Applications

• Integration of the TNM-L Total Nitrogen Unit to assess carbon–nitrogen balance in real time.
• Development of on-line, automated monitoring systems for industrial microalgae bioreactors.
• Extension of TOC analysis to other biomass processes, including wastewater treatment and fermentation.
• Combining TOC data with optical density and fluorescence sensors for multi-parameter control.

Conclusion

The Shimadzu TOC-L CPH analyzer provides a robust, pretreatment-free approach to monitor microalgal growth via direct TOC measurement. The technique yields valuable insights into carbon dynamics, supports efficient culture optimization, and offers a foundation for advanced process control in biofuel research and production.

References

No explicit literature references were provided in the original text.