Enhancing resource recovery and biomass production through microalgae-cyanobacteria binary culture for establishing wastewater-driven peri-urban biorefinery

Abstract

Maintaining monocultures in microalgae cultivation poses operational challenges and increases the financial burden. These challenges can be mitigated by adopting microalgae-cyanobacteria binary cultures. Here, the binary culture of a microalgae Asterarcys sp. BERC16 and cyanobacterium Lyngbya birgei BERC18 were tested against various growth factors, including inoculum ratio, aeration, sterilization, higher N/P ratios, and microbial community for improved resource recovery and biomass production in unsterilized primary-treated urban wastewater. The binary culture demonstrated remarkable efficiency, achieving 97–99 % nitrate removal, reducing its concentration from 210 mg/L to 4.6 mg/L, along with 66 % phosphate removal and a 78 % reduction in chemical oxygen demand. It tolerated up to three times higher N/P concentrations and yielded up to 2.18-fold more biomass compared to monocultures. Notably, cultivating the binary culture in unsterilized primary-treated wastewater enhanced biomass harvesting efficiency to 71 %, attributed to the production of carbohydrate-rich exopolysaccharides. Additionally, binary cultivation significantly reduced bacterial colonies from day zero to harvesting. Preliminary characterization of the harvested biomass revealed a lipid content of 45–53 % and a protein content of 40 %, underscoring its potential for biochemical and biofuel production. This approach offers a promising pathway toward developing a cost-effective and technically viable wastewater-powered biorefinery.