Raceway cultivation of Dunaliella as practiced by NBT Ltd is highly suitable for high yields of carotenogenic biomass and readily scalable to 50 tonnes y-1 or more. The cultivation site in Eilat has lined raceways fitted with paddlewheels and these hold sea- and salt-water maintained at 10-15% salinity to cultivate the halophytic algae. Liquid pressurised CO2 is bubbled in for carbonation for algal growth. Inoculation and scale-up are with smaller raceways. Algae are harvested by partially or completely draining the raceways using centrifuges and stabilised to a powder by spray-drying techniques. Fresh biomass is highly susceptible to deterioration after harvest and not normally shipped. Predators such as Artemia are controlled with traps and filters and with modulation of environmental parameters including increase in salinity. Protozoa infestation is not as easily controlled; protozoa are common in all marine salts and in all ocean or marine waters. They come as cysts and are difficult to eliminate.
Raceways are operated for 300 days per year, in winter (5⁰C - 15 ⁰C) and summer (>40⁰C). Wastewater contains high salt and organic loads and is treated in aeration and settlement ponds then filtered before reuse or discharge to the sea. Spent water cannot be discharged to sea without strict legislative control of the BOD and COD. The Technology Readiness Level (TRL) is at 9.
These raceways have been constructed using ideal materials and a cost-efficient design, and have served as a benchmark for Open Pond Raceway production of Dunaliella. In spring, typical yields are ~300 mg carotene m-2 d-1, (carotenoid : chlorophyll ratio ~10), which at ~8% AFDW carotene content amounts to approx. 4 g AFDW biomass m-2 d-1. The pilot has also supported harvesting trials using Evodos T50 technology and has provided data to inform development and optimisation of the Monzon demo OPR.
You can view more details in the poster.
There is also a full description of the work in this presentation.
For more details contact: Ami Ben-Amotz.