Engineering Chlorella-based consortia for sustainable food wastewater treatment: nutrient recovery, pollutant degradation and advanced harvesting.

Microalgae-based bioremediation of wastewater enables simultaneous nutrient removal and production of value-added biomass. This study systematically evaluated three geographically distinct Chlorella sp. strains for semi-continuous treatment of food wastewater, addressing critical challenges that hinder practical application. All strains demonstrated substantial nutrient removal (NO3--N > 73%, TP > 78%), with film-forming Chlorella sp. CQ uniquely sustaining complete nitrate elimination. This strain simultaneously produced biomass in which essential amino acids accounted for 40% of total amino acids, showing both operational stability and nutraceutical potential. Metagenomic profiling of the associated bacterial community in Chlorella sp. CQ culture revealed complementary contributions to nutrient removal, involving cyanobacterial photosynthetic carbon fixation, nitrogen assimilation and denitrification. To address harvesting challenges, biofilm formation on carriers and hydrogel immobilization strategies were implemented. The Chlorella sp. CQ culture with biofilm carriers achieved near-complete biomass sedimentation within 10 h through induced flocculation, and 1.48-fold increase in maximum biomass accumulation. Notably, both carrier-assisted and hydrogel-based immobilization systems achieved complete degradation of organic pollutants (sodium dodecyl sulfate and organic acids). Transcriptomic analysis of Chlorella sp. CQ under pollutant stress identified upregulation of oxidation-reduction processes, proteasome complex and actin binding as key adaptive responses. This system establishes an integrated approach for sustainable wastewater treatment and resource recovery through microbial consortium selection and advanced harvesting techniques.