Diurnal dynamics of green microalga Tetraselmis viridis culture density in open pond monitored by optical density sensor

Outdoor cultivation of microalgae presents a possibility for obtaining biomass and high-value compounds using natural solar energy, but significant diurnal variation of culture density can occur. Therefore, in this research diurnal dynamics of green microalga Tetraselmis viridis culture density was studied using optical density sensor and an Arduino Nano. The proposed method proved to have high accuracy in the range of biomass concentration from 0.37 to 0.78 g·L−1. Average daily productivity reached 0.098 g·L−1·day−1 (or 5.9 g·m−2·day−1). Biomass/cell density ratio decreased almost two-fold during cultivation, not affecting optical density sensor accuracy. Night biomass loss resulting from respiration consisted from 3.5 % to 22 % of biomass and had positive correlation with culture density, daytime production and culture temperature. Hourly productivity and photosynthesis efficiency varied significantly during light period. The results demonstrate that the proposed method of 24-h algal culture monitoring can provide useful data for obtaining the maximum yield. [Display omitted] •Optical density sensor based on Arduino Nano was used for microalgae culture density monitoring.•T. viridis culture density in open pond had significant diurnal variation.•Average productivity reached 5.9 g·m−2·day−1 with daytime production up to 12.4 g·m−2·day−1.•NBL ranged from 3.5 % to 22 % of biomass, correlating with DW, daytime production and temperature.•Hourly productivity and PE varied significantly due to irradiance and other factors.