Outdoor Cultivation of the Microalga Chlorella vulgaris in a New Photobioreactor Configuration: The Effect of Ultraviolet and Visible Radiation

Abstract

Microalgae can be a future source of biomass with a wide range of applications, including its use to solve current environmental issues. One of the main variables for microalgal cultivation is the light supply: (i) its intensity that often does not present a uniform spatial distribution inside the culture; (ii) photoperiod; and (iii) spectrum. Therefore, this study aims to evaluate the growth of the microalgae Chlorella vulgaris in a tubular photobioreactor with compound parabolic collectors (CPCs) under outdoor conditions. The effect of ultraviolet and visible radiation on biomass productivity and nutrients (nitrogen and phosphorus) uptake was assessed. The maximum biomass productivity was (5 ± 1) × 10−3 g·L−1·h−1, and the specific growth rates ranged from (1.1 ± 0.3) × 10−2 to (2.0 ± 0.6) × 10−2 h−1. Regarding nutrient uptake, initial removal rates of (0.9 ± 0.4) mg N·L−1·h−1 for nitrogen and (0.17 ± 0.04) mg P·L−1·h−1 for phosphorus were reached. These values increased with visible and ultraviolet irradiance until certain values (143 WVIS·m−2 and 9 WUV·m−2 for biomass productivity; 101 WVIS·m−2 and 6 WUV·m−2 for nutrient removal) and then decreased for higher ones due to the photoinhibition phenomenon. Therefore, the application of CPCs to photobioreactors (PBRs) may be beneficial for microalgal culture in countries with higher latitude (with lower solar irradiance levels).

Microalgae Production on Biogas Digestate in Sub-Alpine Region of Europe—Development of Simple Management Decision Support Tool

“…For example, Figler et al [80] conducted experiments cultivating microalgae in different NaCl concentrations (from 500 to 20,000 mg L −1 , corresponding to 800-36,000 µS cm −1 ) and successfully grew Scenedesmus obliquus and S. obtusus even at very high Na + concentrations. The growth inhibition of microalgae when using high EC substrates rich in ammonia-nitrogen (e.g., biogas digestate) is primarily due to the toxic effects of ammonia or other inhibitory substances rather than the salts themselves [81,82], so the dilution of these feedstocks is necessary to reduce the inhibitory effect, which also reduces EC [83].…”

“…The nitrogen removal capacity by assimilation with the microalgae biomass is limited by the maximal productivity in the system, which is determined by the available solar radiation [83,84]. In temperate climates, a maximum of 3.5 g N m −2 day −1 could have been removed if the maximum mean productivity of 50 g m −2 day −1 had been achieved [84].…”

A Critical Review on the Status and Progress of Microalgae Cultivation in Outdoor Photobioreactors Conducted over 35 Years (1986–2021)

“…Solar radiation with different frequencies may have a different impact on a specific algal strain. For example, UV-A radiation does not affect the growth of C. vulgaris but UV-B radiation hurts its growth [61].…”