Simplified and cost-effective modulatory photobioreactor setup for upscaling microalgal culture for research and semi-industrial purposes

Abstract

Algal biomass and algal substances attract much interest from researchers, entrepreneurs, and farmers. Macroalgal biomass can be collected from the wild or cultivated in open tanks with a relatively low risk of contamination; however, achieving a sufficient amount of microalgal biomass is much more challenging, as the study of algal substances requires rather large amounts of biomass for extraction procedures and analyses. Due to budgetary constraints, most research institutes cannot afford to purchase large-scale ready-for-use photobioreactors, and knowledge regarding the self-construction and operation of such systems is not commonly shared. For this purpose, we present a straightforward, cost-effective methodology for modulatory mid-scale microalgal cultivation, using low-cost materials and instruments existing in most laboratories. We purchased a long polyethylene sleeve roll to assemble the photobioreactors and trimmed it to individual sleeves containing up to 20 L of culture medium each. A large medium volume was sterilized using commercial bleach (sodium hypochlorite), followed by dechlorination with thiosulfate. After a cultivation period of 7–14 days, flocculation induction was achieved by adding calcium hydroxide to facilitate an efficient harvest process. Cultures were enriched with CO2 in response to increasing pH throughout the cultivation process using a simple controller. Using an isolate of one of our species of interest, Mucidosphaerium pulchellum, we demonstrated how using one pH regulatory system can regulate a set of cultures (each in a different sleeve) to remain in the pH range 7.4–8.1 while saving CO2. This economical CO2-enrichment method increased algal growth rates by 23 %, reaching ca. 20 % higher total suspended solids compared to air-supplemented cultures. Such a cultivation system can be implemented with a surprisingly low budget of only USD800, efficiently producing hundreds of grams of biomass per cultivation period to support research on highly nutritious substances production and bioactive compounds discovery.