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

Abstract

Microalgae, a renewable bio-resource, are considered a potential value-added commodity and a tool to combat climate change. Microalgal research has received worldwide attention recently. Different perspectives have been explored, but cultivation in outdoor photobioreactors (PBRs) is still a less explored field. This review summarizes the studies conducted on the microalgae cultivated in outdoor PBRs only. The locations, algal strains, PBRs, and cultivation media used in these studies were identified and tabulated. Different aspects of outdoor algal cultivation in PBRs, such as temperature control, light intensity control, photosynthetic efficiency (PE), the outdoor adaptation of strains, PBR designs, and algal growth and biochemical composition variation from the weather, were studied and reviewed. A brief review of downstream processes and environmental and economic impacts was also conducted. This review summarizes what has been carried out in this field so far and will help researchers to determine what further work needs to be conducted and in which direction to proceed.

Applications of Microalgae in Foods, Pharma and Feeds and Their Use as Fertilizers and Biostimulants: Legislation and Regulatory Aspects for Consideration

“…Microalgal production is still a small-scale activity because the high growth rate and productivity often observed at the laboratory scale is difficult to replicate at an industrial scale. Using outdoor cultivation conditions, the duplication time for microalga and the biomass productivity decreases (by as much as 40 t ha −1 per year) [43][44][45][46] compared to what is observed in the laboratory. Productivity of algae in terms of growth is usually lower in outdoor environments compared to laboratory environments because the temperature and light intensities outdoors are more variable and extreme [47].…”

“…The initial growth environment can therefore limit use of algae especially for feed, food and pharmaceutical purposes. Growth conditions also impact the potential to use algae as fertilizers and even their potential to be used as fuel feedstock as heavy-metal bioaccumulations could affect fuel properties and the composition of emissions [46].…”

“…In addition, there is the possibility of biomass contamination with pathogens present in harvested biomass or in the final process effluent when microalgae are cultivated with wastewater sources. This may present a potential health risk [46]. In addition, microalgae producers must become knowledgeable on the legislation governing the use of microalgae as/or in food and feeds, and they must be compliant with what is required to obtain an ecological footprint certification, and the Nagoya Protocol.…”

A Green Revolution in Antioxidant Research: Harnessing Microalgae for Wellness and Longevity

“…The sustainable production and cultivation of microalgae involve the use of various cultivation systems, with photobioreactors and open ponds being the two primary methods for large-scale production [97].…”

“…These closed cultivation systems offer several advantages. Photobioreactors allow precise control of temperature, light intensity, pH, and nutrient concentration, which helps maximize microalgae growth and productivity [97,98]. The closed nature of photobioreactors minimizes the risk of contamination from external sources, such as competing microorganisms or pollutants.…”