Improving biomass yields of microalgae biofilm by coculturing two microalgae species via forming biofilms with uniform microstructures and small cell-clusters

[Display omitted] •Microalgae biomass of cocultured biofilm (CB) was related to biofilm microstructure.•Biofilm porosity was not the only structural parameter affecting biomass yields (BY).•Biofilm with more uniform structure and fewer cell-clusters contributes to higher BY.•BY of S. obliquus-C. pyrenoidosa CB was 37 % higher tahan uni-species culture.•Spherical cells with fewer surface polymers formed uniform biofilm microstructure. Microalgae coculture has the potential to promote microalgae biofilm growth. Herein, three two-species cocultured biofilms were studied by determining biomass yields and detailed microstructure parameters, including porosity, average pore length, average cluster length, etc. It was found that biomass yields could reduce by 21–53 % when biofilm porosities decreased from about 35 % to 20 %; while at similar porosities (∼20 %), biomass yields of cocultured biofilms increased by 37 % when they possessed uniform microstructure and small cell-clusters (pores and clusters of 1 ∼ 10 μm accounted for 96 % and 68 %, respectively). By analyzing morphologies and surface properties of cells, it was found that cells with small size, spherical shape, and reduced surface polymers could hinder the cell-clusters formation, thereby promoting biomass yields. The study provides new insights into choosing cocultured microalgae species for improving the biomass yield of biofilm via manipulating biofilm microstructures.