Treatment of highly saline RO concentrate using Scenedesmus quadricauda for enhanced removal of refractory organic matter

This study achieves a better understanding how Scenedesmus quadricauda microalgae participate in the phycoremediation of a reverse osmosis (RO) concentrate at a high salinity (8000 mg Cl⁻ L^{− 1}). Algal treatment of the RO concentrate under continuous illumination resulted in a notable increase in the biodegradability of dissolved organic matter, subsequent removal of biodegradable fractions, and simultaneous removal of nutrients (N and P). This is the first time that S. quadricauda is shown to induce the degradation of polymeric organic matter in the RO concentrate, which is typically refractory to microbial decomposition. In this study, the mechanisms for algae-induced degradation were investigated by measuring the hydrogen peroxide (H₂O₂) released out of algal cells and dispersed in the aqueous phase. The algae-induced biodegradation process has an advantage over typical electrochemical oxidation technologies in that photo-sensitive living organisms are capable of self-repair, reproduction, and nutrient uptake. Our results indicate that the use of algae-induced oxidation is highly feasible as a safe, inexpensive technology to pre-treat non- or slowly-biodegradable organic matter in wastewater prior to downstream biological processing.