The desalination of an Arthrospira platensis feed solution byelectrodialysis and reverse osmosis

For long-term space missions, the algae Arthrospira platensis (previously Spirulina platensis) can be used as a foodcomponent. A. platensis can be cultured in a Zarrouk medium (further called “medium”) which contains several salts. As a result, the cultured cells have to be washed to make them edible. In space these salts have to be recovered to maintain the medium and consequently reduce the uploaded mass. Reverse osmosis (RO) and electrodialysis (ED) were tested for me desalination of the pure medium as me worst-case scenario. Separation performance, energy requirements and potential for application in space were compared for both processes. Three RO membranes were tested while ED tests were performed at different voltages and at varying diluate/concentrate ratios. Energy calculations for the ED revealed the effects of voltage levels and processing time required for desalination. The energy requirement was calculated to be slightly higher for ED than for RO; however, the performance of both techniques is comparable. For space applications other system aspects such as weight and footprint have to be taken into account. When RO and ED are tested, ED is a better candidate for this application since RO needs a heavy, high-pressure pump (weight disadvantage). Moreover, the pump might cause vibrations which should certainly be avoided for space applications. Another advantage of ED is that the final salinity of the diluate can be adjusted if required.