Raceway cultivation of Dunaliella as practiced by Monzon Biotech is highly suitable for high yields of carotenogenic biomass and readily scalable to 50 tonnes y-1 or more. At the cultivation site in Monzon, Spain, the halophytic Dunaliella algal strains are cultivated in brine, which is sourced from shallow underground salt deposits infused with freshwater. During summer, fresh water is added with the brine to balance the evaporation losses and maintain 15-25% salinity throughout the year. There are few predators because the brine comes from inland sources of salt. The raceways are lined and fitted with paddlewheels, and also have a heating system for temperature control in winter, established with excess low grade heat from a 14MW CHP plant. Flue gas CO2 from natural gas combustion by the CHP plant (up to 7% CO2) is bubbled in for carbonation for algal growth and smaller raceways ae used for inoculation and scale-up purposes. Algae are harvested by partially or completely draining the raceways using centrifuges and stabilised by freeze-drying techniques. Treated wastewater is injected back into empty underground salt caverns. Freshly harvested wet biomass is highly susceptible to deterioration after harvest and is therefore normally shipped under vacuum after freeze-drying to a powder. Raceways are operated for 300 days per year, in winter (5⁰C - 15 ⁰C) and summer (>40⁰C) and current biomass productivity ranges have been calculated to lie between 0.75 g m-2 d-1 and 3.0 g m-2 d-1 depending on seasonality and other factors. The Technology Readiness Level (TRL) is at 9.
In the D-Factory project the pilot Open Pond Raceways at Monzon were optimised for temperature and algal CO2 capture from flue gas and operated to provide freeze-dried Dunaliella biomass for downstream processing as well as data for sustainability assessment and business planning purposes. The raceways also supported harvesting trials using Evodos T10 technology and investigation of the utility of using PBRs supplied by A4F as an inoculation system. The algal strains were shown to be related to D. salina bardawil and some of these e.g. DF40 are now cryopreserved and held at the Marine Biological Association Culture Collection. An Integrated Assessment of Sustainability of a CO2 Microalgal Biorefinery recommended the practice of integrating algal cultivation with salt activities; using flue gas and waste heat from a power plant; avoiding using arable land and guaranteeing sufficient availability of freshwater and this know-how is now demonstrated at the Monzon pilot facility in Spain.
You can view more details in the poster "Sustainable Cultivation of Dunaniella salina in an Industrial-scale D-Factory Biorefinery".
For more details on integrated life cycle sustainability assessments contact: Carlos Casanovas