Biodesalination of saline aquaculture wastewater with simultaneous nutrient removal and biomass production using the microalgae Arthrospira and Dunaliella in a circular economy approach

Freshwater scarcity is escalating due to factors such as climate change, droughts, increased demand, population growth, and poor water management practices. A promising sustainable solution to this challenge is biodesalination using microalgae. We demonstrate that Arthrospira platensis and Dunaliella salina can thrive in saline aquaculture wastewater, reducing both its salinity and the concentration of nutrients. The salinity removal ability was quantified through measurements of electrical conductivity (EC) and ICP-OES, revealing reductions in EC by up to 45 % (from 31.5 to 17.2 ms/cm) for A. platensis and 35 % (from 31.5 to 20.5 ms/cm) for D. salina. FESEM indicated the formation of a salt layer on the surface of both microalgae, suggesting biosorption and bioaccumulation as likely mechanisms. FTIR spectroscopy analysis demonstrated the binding of functional groups within the cell wall of A. platensis and the cell membrane of D. salina with the ions present in the medium. Scaling up the cultivation of A. platensis in a photobioreactor under non-sterile conditions validated the processes' potential for industrial-scale biodesalination. Although the treated water did not reach the standards for irrigation or potable use, this approach provides a preliminary desalination step, reducing burden on subsequent treatments and simultaneously providing nutrient removal and biomass production.