Industrial microalgae production for aquaculture hatcheries

In this thesis the cost price of microalgae production in aquaculture hatcheries and the effect of cost reduction strategies on the biomass quality is studied. The cost price of microalgae production in aquaculture hatcheries and cost reduction strategies is described with a techno-economic model using Rhodomonas sp. as an example species for microalgae production in aquaculture. The effect of growth conditions on the biomass yield on light and the biomass quality is studied on both laboratory scale and pilot scale.A techno-economic model to describe the cost price for microalgae cultivation in aquaculture hatcheries was developed. The model is based on inputs from hatcheries in the Dutch aquaculture industry. The calculations compare modular production systems (bubble-columns) and scalable production systems (tubular photobioreactors). On a production scale presently applied in Dutch aquaculture hatcheries (125 kg year-1) the modular reactor systems result in a biomass cost price of €587,- kgDW-1 for production under artificial light and €573,- kgDW-1 using sunlight. The scalable production systems result in lower production costs with €290,- kgDW-1 using artificial light and €329 kgDW-1 with sunlight. The most efficient cost reduction strategies are identified as: 1) increasing biomass yield on light, 2) applying more artificial light and 3) reducing labor requirements. The cost price can be reduced to € 96,- kgDW-1 by implementation of cost reduction strategies at the same scale (20 m2) using scalable production under artificial light conditions. Production of biomass at a larger scale (1500m2) using scalable production systems combined with cost reduction strategies can result in a cost price of €23,47 kgDW-1.Using the algae Rhodomonas sp. as example species for algae in aquaculture, the growth of this strain under continuous cultivation conditions was characterized. The effect of light (60-600 µmol m-2 s-1) and temperature (15-30 °C) on the growth rate, biomass production rate, biomass yield on light and the fatty acid content and composition was studied. Growth rates of > 1.0 d-1, with biomass production rates up to 1.5 g l-1 d-1 are described. The highest biomass yield on light (0.87 g mol-1) is found at a temperature of 22-24 °C and light intensity of 110-220 µmol m-2 s-1. The total fatty acid content fluctuates between 8-10% of the dry-weight with an EPA+DHA concentration of 14-25% of the total fatty acids. The total fatty acid content and EPA and DHA content of the cells was only influenced by the cultivation temperature.The effect of daily oscillations of temperature and light on the biomass yield on light and on the biomass fatty acid content and profile was studied. Under the optimized growth conditions for biomass yield on light for continuous conditions, the oscillations of both light and temperature in a 16:8 day:night cycle did not result in an increase of the biomass yield on light. At higher light conditions (600 µmol m-2 s-1) a 22% increase of the biomass yield on light of was found with a day:night cycle compared to continuous light. In a day:night cycle with daily oscillations for light and temperature the fatty acid content and compositions of the cells varied greatly with the moment of the day. Highest total fatty acid concentrations (91 ± 4 mg gDW-1) were found in the first hours after sunrise whereas the highest EPA+DHA content (16 ± 1 mg gDW-1) is found at the end of the night period.Pilot-scale experiments with Rhodomonas sp. in tubular photobioreactors were performed to test the large scale potential of this algae. Successful cultivation of Rhodomonas sp. at pilot-scale using sunlight conditions is described for the first time in literature. Rhodomonas sp. was produced over a period of 6 months, from February till July representing all sunlight conditions available in the Dutch climate. An average biomass yield on light of 0.29 ± 0.16 g mol-1 was obtained, which is lower that the yields obtained in the laboratory experiments. The biomass production rates obtained (250m2 when using scalable production systems when implementing a day:night cycle. Considering all experimental data and inputs on the techno-economic model it is concluded that the production of microalgae for aquaculture hatcheries should be performed using artificial light and scalable production systems. The implementation of a centralized microalgae production facility will result in a great cost price reduction. A cost reduction of 80% can be achieved if algae production of ten hatcheries is combined in a production facility utilizing scalable production systems, compared to individual hatcheries maintaining a modular microalgae production facility