Promoting algae separation of forward osmosis by peracetic acid and chitosan quaternary ammonium salt: Purification efficiency, membrane fouling alleviation, and lipid production

Forward osmosis (FO) is a prospective technology for microalgae biomass recovery, whereas severe membrane fouling still limits its application. To improve the separation efficiency of FO, peracetic acid (PAA) oxidation followed by chitosan quaternary ammonium salt (HTCC) coagulation was proposed. The synergistic effect of PAA-HTCC on the characteristics of Chlorella vulgaris and the separation performance of FO were systematically studied, and the mechanism was revealed. With PAA-HTCC treatment, the harvesting efficiency of algal cells was increased to 88.5 %, and algal aggregates with sizes of 100–300 μm were formed while maintaining excellent cell viability. Membrane fouling caused by microalgae was mitigated, with the water flux increased from 15.0 to 19.2 L/(m²·h), and the recovery flux increased to 90.0 %. The lipid production capacity of microalgae was significantly promoted, with the lipid productivity increased from 10.5 to 27.9 mg·L⁻¹·d⁻¹. During PAA oxidation, ^•OH and ^•CH₃ were the major reactive species, which could remove electronegative organics coated on algal cells, contributing to the aggregation of microalgae in the coagulation by HTCC. Moreover, PAA-HTCC could also provide carbon sources for microalgae growth, thus the water purification efficiency of FO and the lipid production of concentrated microalgae were simultaneously promoted. The proposed strategy has certain significance for water purification and resource utilization of algae.