In aquaculture, specifically for hatcheries or copepod production, the use of the microalga Rhodomonas sp. has increasingly gained research interest over the past few years. While efforts to optimize the cultivation of the strain have been studied in detail under laboratory conditions, it has never been grown in photobioreactors at large scale under outdoor light conditions due to its difficulty to grow in mass-culture.
The growth of Rhodomonas sp. using only sunlight conditions has never been shown before and the behavior of this strain in tubular reactors has not been described with enough detail to allow scale-up to industrial processes. To study the industrial potential of this strain, a team of researchers cultivated Rhodomonas sp. in three identical tubular photobioreactors with 200 liters working volume each, located in a greenhouse using sunlight conditions only. Growth experiments were performed from February with winter light conditions (−2 d−1) up to high light conditions of summer (>50 mol m−2 d−1) in July, representing all sunlight conditions in the Netherlands. All nutrients were supplied in surplus and temperature and pH were maintained at optimum values for growth based on lab data.
Researchers found that biomass productivities increased with increasing light from 0.09 ± 0.04 g l−1 d−1 to 0.19 ± 0.06 g l−1 d−1, for 0–10 and 30–40 molph m−2 d−1. A two to five-fold increase in biomass productivity was obtained compared to previous reports on Rhodomonas sp. cultivation using artificial light at a large scale.
Rhodomonas sp. was successfully cultivated at pilot-scale utilizing the sunlight conditions of the Dutch climate from February until July. This is the first reported cultivation of this microalgae at a pilot-scale utilizing natural sunlight conditions. Based on the literature of Rhodomonas sp. production at lab scale and in comparison to the cultivation of other algae species at pilot-scale outdoors, a large potential for future improvement is still possible. Lab-scale studies of Rhodomonas sp. with high light levels should determine the further possible improvements of Rhodomonas sp. as an industrial production strain for aquaculture using sunlight conditions.
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