Exploiting desalination brine for microalgal biomass production and sustainable brine valorization

To reduce the environmental footprint of desalination brines, modern research focuses on valorization, transforming brine from waste to a resource. Our study is the first in Qatar on the use of cultivating microalgae directly in desalination brine from the region, highlighting its potential as a sustainable and low-cost medium for biomass production and brine valorization. The chemical composition of seawater desalination brine includes essential microelements to support the microalgal growth. Our study investigated crude reverse osmosis (brine RO; 74 ppt), multi-stage flash (MSF; 68 ppt), and diluted OUTPUT brine (a mixture of RO, MSF, and seawater; 50 ppt) for the potential cultivation of Chlorocystis sp. and Halospira sp. Our results revealed the positive influence of nitrate supplementation, with OUTPUT brine yielding the highest biomass productivity in both strains, respectively (0.092 and 0.22 g/L/day) and increased protein content (9 and 64%) compared with controls. High salinity (RO brine) was detrimental to algae growth and resulted in lower productivity in both strains. Halospira sp. cultivated in OUTPUT brine also demonstrated elevated phycocyanin content (29 mg/g). A sequencing batch raceway cultivation strategy was implemented in outdoor raceway ponds, which enhanced the biomass productivity (0.14 g/L/day).