Evaporation reduction and salinity control in microalgae production ponds using chemical monolayers

Abstract

Algae have great potential as a hyper-productive crop to produce food, fuels, and chemicals. However, freshwater availability limits their widespread application. Here we investigate whether chemical monolayers can reduce evaporation in microalgae cultures, and whether algal growth is affected. Thin-film monolayers were formed on the surface of freshwater (Chlorella vulgaris) and marine (Nannochloropsis salina) algae cultures using ethylene glycol monooctadecyl ether. Monolayers applied daily reduced evaporation in both cultures by 70 % on the first day, and ~50 % by day 3. The cause of the reduced performance was investigated but could not be directly attributed to any particular cellular activity or chemical change. Nannochloropsis was uninhibited by the monolayer, while the growth of Chlorella decreased by 38 % over 3 days. There was no evidence that the monolayer reduced gas exchange (CO2/O2), but the reduced growth of Chlorella could have been caused by direct chemical inhibition by the monolayer or the slightly elevated temperature (1–2 °C) resulting from the reduction in evaporative cooling. A techno-economic analysis indicated that water savings could make monolayers economically beneficial, especially in arid climates suited to algae production. In addition, monolayers enable control of salinity in marine production systems. Overall, the application of monolayers to reduce evaporation from outdoor algae cultures has great promise, with testing in outdoor trials an obvious next step.