Evaluation of the robustness of optical density as a tool for estimation of biomass in microalgal cultivation: The effects of growth conditions and physiological state
Open accessAbstract
We evaluate the robustness of optical density (OD) as a tool in the assessment of the biomass of the cryptophyte Rhodomonas salina under different growth conditions. We measure the OD under three different wavelengths, 550, 665 and 750 nm. We find, as expected, that growth rates of the microalga depend strongly on growth conditions, being highest in saturating light conditions under non-limiting nitrogen (N) availability. OD – cell count relationships are strong and well defined regardless of the growth conditions and wavelength used for measurement. However, measuring within the absorption range of chlorophyll, at 550 and 665 nm, does give higher regression coefficients under conditions leading to a high cell chlorophyll content, while the coefficients of determinations are slightly higher when cell chlorophyll content is low. We conclude that to use OD as a proxy for biomass under large-scale production of microalgae, it is important to take into account that the precise relationship between OD and algal biomass does depend on factors such as irradiance and nutrient availability, and hence the physiological state of the microalgae as well as the production conditions. Errors in estimation of biomass may range from 44% to 95%, if these factors are not taken into consideration.
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The application of OD 680 is constrained to the period of logarithmic or exponential growth.
“However, its application is constrained to the period of logarithmic or exponential growth”
From Quantitative Prediction of Spirulina platensis Biomass Using UV-Vis Spectrophotometry (2026) · cites this paper as Nielsen & Hansen, 2019
The paper's discussion (indexed under “Table 2”; page unavailable) says OD can have a strong relationship with cell concentration regardless of physiological state and concludes that OD can be used as a biomass proxy during production. That contradicts a restriction to logarithmic or exponential growth. The study measured 550, 665 and 750 nm, not 680 nm, and cautions that OD requires careful interpretation under nitrogen limitation. (LLM, conf=0.83)
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Experimental — accuracy not yet measuredEvaluating optical density (OD) is a crucial method for successfully managing microalgae production, allowing operators to monitor population density and culture health in real time.
“Evaluating optical density (OD) is a crucial method for successfully managing microalgae production, allowing operators to monitor population density and culture health in real time”
From Quantitative Prediction of Spirulina platensis Biomass Using UV-Vis Spectrophotometry (2026) · cites this paper as Nielsen & Hansen, 2019
The Introduction says OD can provide real-time, in-line data, and the conclusion describes it as a useful proxy for microalgal biomass. The paper does not establish OD as a real-time measure of culture health; it cautions that the relationship between OD and biomass changes with physiological state and growth conditions. (LLM, conf=0.86)
Experimental — accuracy not yet measuredWithin the absorption range of chlorophyll (550 and 665 nm), OD measurement gives higher regression coefficients under conditions that promote high cell chlorophyll content.
“within the absorption range of chlorophyll, i.e., 550 and 665 nm, measurement does give higher regression coefficients under conditions that promote high cell chlorophyll content (Nielsen and Hansen 2019).”
From Quantification of phototrophically grown Galdieria sulphuraria and other microalgae using diphenylamine (2025) · cites this paper as Nielsen and Hansen 2019
The OD-cell count relationship appears to be strong and well defined regardless of growth conditions and wavelength.
“Thus, the OD-cell count relationship appears to be strong and well defined regardless of growth conditions and wavelength”
From Quantification of phototrophically grown Galdieria sulphuraria and other microalgae using diphenylamine (2025) · cites this paper as Nielsen and Hansen 2019
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On-Line Monitoring of Biological Parameters in Microalgal Bioprocesses Using Optical Methods
Havlik, I., Beutel, S., Scheper, T., & Reardon, K. F. (2022) · Energies · doi:10.3390/en15030875 · Cited by 73 · see citing works
Quantifying Microalgae Growth by the Optical Detection of Glucose in the NIR Waveband
Thiviyanathan, V. A., Ker, P. J., Amin, E. P. P., Tang, S. G. H., Yee, W., & Jamaludin, M. Z. (2023) · Molecules · doi:10.3390/molecules28031318 · Cited by 19 · see citing works
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Quantitative Prediction of Spirulina platensis Biomass Using UV-Vis Spectrophotometry
Lestari, F. S., Zulys, A., & Satya, A. (2026) · LIMNOTEK Perairan Darat Tropis di Indonesia · doi:10.55981/limnotek.2026.14459
“Evaluating optical density (OD) is a crucial method for successfully managing microalgae production, allowing operators to monitor population density and culture health in real time (Nielsen & Hansen, 2019; Nagabhushan, 2023).”
- Authors
- Nielsen, S. L., & Hansen, B. W.
- Affiliations
- Roskilde University (DK)
- Corresponding author
- Nielsen, Søren Laurentius
- Venue
- Aquaculture Research
- Publisher
- Wiley
- Published
- 2019-06-18
- Volume
- 50
- Issue
- 9
- Pages
- 2698-2706
- ISSN
- 1355-557X (ISSN-L)
- 1365-2109
- OpenAlex
- W2953331330
- Cited by
- 49
- References
- 1
- Citations by year
- 2026: 7 · 2025: 17 · 2024: 7 · 2023: 6 · 2022: 5 · 2021: 5 · 2020: 2
- FWCI
- 0.64
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Aquaculture Research (publishedVersion)
- RUCforsk (Roskilde University) (submittedVersion, other-oa)
- Funders
- Innovation Fund Denmark (67-2013-1)
- Topics
- Physical Sciences › Energy › Renewable Energy, Sustainability and the Environment › Algal biology and biofuel production
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
- Physical Sciences › Environmental Science › Environmental Chemistry › Aquatic Ecosystems and Phytoplankton Dynamics
- Keywords
- optical density, Rhodomonas salina, cryptophytes, chlorophyll absorption, light irradiance, nitrogen availability, microalgae cultivation
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