Effect of Illumination Colour on the Growth and Energetic Properties of Chlorella vulgaris for Bioenergy Applications

Microalgae are a promising third-generation biomass resource due to their high photosynthetic efficiency, rapid growth rates, capacity to accumulate energy-rich biochemical fractions, and efficient utilisation of carbon dioxide (CO2). In this study, the effect of illumination colour on the growth and energetic properties of Chlorella vulgaris cultivated in laboratory-scale photobioreactors was investigated. Four independent cultivation cycles were conducted under controlled conditions using a 16 h light/8 h dark photoperiod, temperatures of 20–30 °C, and aeration with air enriched with 10% CO2. Cultures were illuminated using six light colours: plant-specific, white, green, red, blue, and ultraviolet. Biomass productivity was quantified, and the higher heating value (HHV) of the produced biomass was determined by bomb calorimetry. In addition, proximate (technical) analysis was performed for Chlorella vulgaris and compared with Chlorella pyrenoidosa, Spirulina, and Fucus vesiculosus (bladderwrack). The results showed that white illumination promoted both the highest biomass growth and the highest HHV for Chlorella vulgaris (15.08 MJ·kg−1), while ultraviolet illumination had a disruptive effect, leading to the lowest growth and calorific value (11.49 MJ·kg−1). Comparative analysis revealed that Chlorella pyrenoidosa exhibited the most favourable energetic properties; however, Chlorella vulgaris remains attractive for cultivation due to its robustness and broad tolerance to operating conditions.