Characterization of two microalgae consortia grown in industrial wastewater for biomass valorization

The use of microalgae-bacteria consortium coupled with biomass valorization is promising for environmentally friendly and economical wastewater treatment. However, a significant challenge associated with microalgae consortia grown in wastewater is predicting how different species will grow together and how this will affect both, the composition and the productivity of different batches. Therefore, this study aimed to examine microbiome associated with a green alga consortium versus a cyanobacteria consortium, both evolved from the same initial consortium, to compare their wastewater treatment efficiency as well as the metabolites of interest produced. Cultures of both consortia were conducted in a semi-continuous mode in 2 L photobioreactors for 51 days with standard culture medium with or without wastewater. Analysis of individual OTUs (operational taxonomic units) from the microbial community revealed that 1) Trebouxiophyceae and Gomphosphaeriaceae are the most abundant organisms in the green algae and cyanobacteria consortia respectively; and 2) both consortia shared 28% and 15% of identified prokaryotes and eukaryotes OTUs, respectively. Although the cultures enriched with wastewater did not achieve the yields obtained with a standard medium, growth was observed with a nutrient removal efficiency up to 91% and 63% for total nitrogen and total carbon respectively. The algal biomass as well as the supernatants from the two consortia were analyzed by UPLC-QTOF-MS and GC–MS. Results showed valuable bioactive compounds such as lecanoric acid (antimicrobial, antioxidant and anticancer) and high added-value lipids. Also, polyunsaturated fatty acids were the most abundant fatty acids in our samples (51% to 66%). Results suggest that even though an initial native consortium evolved into two different consortia, both can grow in presence of wastewater. Moreover, both were able to remove a high part of nitrogen and carbon while producing interesting compounds, which paves the way for a potential economically viable wastewater treatment process.