Microalgae-bacteria consortia for the treatment of raw dairy manure wastewater using a novel two-stage process: Process optimization and bacterial community analysis

The major objective of this study was to develop a functional microalgae-bacteria consortium for the treatment of dairy manure wastewater (DMW). Chlorella sorokiniana AK-1 was selected as the proficient microalgal strain for treating unsterilized DMW. AK-1 was directly grown in 50% raw DMW, and the addition of an acclimated mixed bacterial culture enriched from dairy manure improved treatment efficiency. Culture conditions for DMW treatment using the AK-1 mixed bacterial consortium were optimized as follows: 50% raw DMW, 0.4 g/L mixed bacterial inoculum on day 1, followed by 0.1 g/L AK-1 inoculum on day 3, and further incubation for 3 days. The achieved removal efficiencies for COD, BOD, TN, NH3-N, and TP were 84.3%, 97.8%, 90.2%, 99.1%, and 100%, respectively. Bacterial 16S rDNA sequencing was conducted to analyze the shift in the bacterial community during wastewater treatment. In DMW, Firmicutes emerged as the dominant phylum, whereas Proteobacteria took over after microalgal inoculation. Additionally, Actinobacteria and Bacteroidetes were consistently present in all samples. Interestingly, Patescibacteria and Planctomycetes were found in varying proportions. At the species level, the predominant bacteria identified during the treatment process were Rhizobiaceae, Sericytochromatia_unclassified, Pirellula_sp, Owenweeksia, Devosia_unclassified, Acinetobacter_towneri, and Acinetobacter_unclassified. Despite the significant diversity of the microbial community among the different processes, optimal microalgal biomass production and maximum nutrient removal efficiencies were achieved using this designer microalgae-bacteria consortium.