Validating Spectrophotometry and Aquapen for Microalgae Density Assessment

Abstract

Estimation of algae density during water quality assessment and laboratory or industrial processes requires a simple, sensitive, and accurate method. Two widely used techniques for this purpose are spectrophotometry and the AquaPen fluorometer. This work outlines and validates the laboratory protocols for quantifying algal density in freshwater samples, an essential step in assessing water quality. A UV-Visible spectrophotometer was employed to determine absorbance or the optical density (OD) and infer Chlorophyll-a (Chla) concentration, while the AquaPen fluorometer assessed chlorophyll fluorescence (Fv/Fm) parameters indicative of algal (Nitzschia palea) photosynthetic activity during a culturing period of 14 days. Additionally, nutrient levels, including nitrogen and phosphorus were also analyzed using a spectrophotometer to correlate with algal biomass. The highest OD was recorded on day 8 and 14, corresponding to the highest cell density recorded (7.6 x 107cells/L). The highest concentration of chlorophyll- a was also recorded on day 14 (1253.8 mg/L). PCA-Biplot analysis show that there is a positive correlation between OD, cell density, chlorophyll-a, nitrogen and phosphate. The integrated use of these instruments provides a robust framework for monitoring phytoplankton dynamics in aquatic ecosystems.