Pilot-scale cultivation of the red alga Porphyridium purpureum over a two-year period in a greenhouse

Abstract

Microalgae can form renewable feedstock for many sectors. However, most microalgae commercially cultivated are difficult to grow in colder climates. To overcome this problem one could cultivate cold tolerant algae. One such alga is the red marine alga Porphyridium purpureum. It is currently often cultivated in bag systems in limited volumes. In this study we cultivated P. purpureum at pilot-scale in horizontal tubular reactors in a greenhouse. P. purpureum was grown in batch mode in a total volume of either 350, 500, 1000 or 1500 L. A total of 28 batches, spread over two years, were cultivated reaching a maximum dry weight of 1.94 g L−1. The growth was continuously monitored to calculate the productivities and growth rates. The P and N concentrations were measured frequently during four batches to calculate the P and N usage per gram biomass. To calculate CO2 fixation efficiencies the total CO2 consumption was monitored during 6 of the 28 batches. A maximum productivity and growth rate of respectively 0.195 g L−1 day−1 and 0.233 day−1 were achieved while the P and N usage varied from 3.2–6.19 and 14.5–36.6 mg g−1 biomass for P and N, respectively. Growth was supported between 10 °C and 30 °C, while temperatures above 34—35 °C proved to be detrimental. The CO2 efficiencies differed among the 6 tested periods with the highest utilization efficiency being 13.5% and the lowest a mere 1.5%. Further large-scale, continuous, tests would be needed to fully optimize the cultivation of P. purpureum in larger volumes.