Assessment of key biological and engineering design parameters for production of Chlorella zofingiensis (Chlorophyceae) in outdoor photobioreactors

Abstract

For the design of a large field of vertical flat plate photobioreactors (PBRs), the effect of four design parameters-initial biomass concentration, optical path length, spacing, and orientation of PBRs-on the biochemical composition and productivity of Chlorella zofingiensis was investigated. A two-stage batch process was assumed in which inoculum is generated under nitrogen-sufficient conditions, followed by accumulation of lipids and carbohydrates in nitrogen-deplete conditions. For nitrogen-deplete conditions, productivity was the most sensitive to initial biomass concentration, as it affects the light availability to individual cells in the culture. An initial areal cell concentration of 50 g m(-2) inoculated into 3.8-cm optical path PBR resulted in the maximum production of lipids (2.42 ± 0.02 g m(-2) day(-1)) and carbohydrates (3.23 ± 0.21 g m(-2) day(-1)). Productivity was less sensitive to optical path length. Optical path lengths of 4.8 and 8.4 cm resulted in similar areal productivities (biomass, carbohydrate, and lipid) that were 20 % higher than a 2.4-cm optical path length. Under nitrogen-sufficient conditions, biomass productivity was 48 % higher in PBRs facing north-south during the winter compared to east-west, but orientation had little influence on biomass productivity during the spring and summer despite large differences in insolation. An optimal spacing could not be determined based on growth alone because a tradeoff was observed in which volumetric and PBR productivity increased as space between PBRs increased, but land productivity decreased.

Opportunities to improve the areal oil productivity of microalgae

“…Although solar irradiation provides a given incident light intensity to a certain ground area, smart use of refraction and reflections at the reactor surface can distribute this incident light over a larger reactor area without reducing the total amount of light provided to the culture; a principle called light dilution (Slegers et al, 2011;Wijffels and Barbosa, 2010;Zemke et al, 2013) (Supplementary Fig. 6).…”

Cytotoxic effect of extract from Dunaliella salina against SH-SY5Y neuroblastoma cells

“…It has been shown that the potential of biotechnological use of Chlorophyceae family members is becoming more important especially in the field of sustainable and recyclable, clean energy production (Li et al 2011). For this reason, large-scale production processes have been successfully optimized in both open and closed production systems, particularly for Dunaliella, Spirullina, Chlorella, Scenedesmus algae species (Rastogi and Incharoensakdi 2013;Zemke et al 2013;Fu et al 2014).Therefore, it is hypothesized that the production of potential drug molecules from algae species via using already well-optimized large-scale production systems is highly possible.…”

Antenna size reduction in microalgae mass culture

“…Technical solutions to improve the light intensity distribution in the photobioreactor are at hand, but this principle of light dilution (Tredici et al 1998, Dye et al 2011, Zemke et al 2013) often leads to high material costs while in the end, the surplus of light absorption should be regarded as a problem of biological origin. …”

“…By improving the light energy distribution within the reactor, the effects of oversaturation are alleviated. To date, the concept of light dilution is a frequently employed approach to optimize photobioreactor performance by increasing its surface area per unit of reactor (Tredici et al 1998, Dye 2010, Zemke et al 2013) whereby the light use efficiency can be increased. However, physical and economic limits are being reached in the context of the hardware while there continues to be opportunities for improvement in relationship to biology.…”

“…In addition, microalgae have a high pigment content to be able to survive under low light conditions. Technical solutions to minimize light absorption per cell and provide a better light distribution in the photobioreactor are at hand, but this principle of light dilution (Tredici et al 1998, Dye et al 2011, Zemke et al 2013 often results in high photobioreactor material costs. Photosystem oversaturation is a biological problem and the most effective solution would therefore be to prevent that oversaturation occurs by means of genetic engineering (Chisti 2007).…”