Characteristics of fast-sedimenting, floc-forming microalgae-bacteria consortia used for bioremediation.

The microalgae-bacteria consortia (MBC) described here can be used for the cost-efficient and continuous production of biomass in photosynthetic, chemostatic bioreactors. In order to obtain its characteristic sedimentation behavior by passive gravitation, it is necessary to repeatedly select environmental samples for floc-forming and fast-sedimenting structures. After selection, these floc cluster mainly contain microalgae, cyanobacteria and other bacterial species. Comparative studies with unialgal cultures have been conducted, which have revealed exceptional sinking properties of the acquired MBC cultures (recovery rate: 97.48 ± 2.30%; mean sinking velocity: 4.16 ± 0.52 m h ^− 1 ; mean particle size: 417.59 ± 21.82 µm). Furthermore, experiments with the MBC adapted to three different types of substrate (sewage, artificial medium and fish sewage) revealed the substantial dependency of the applied substrate and the floc morphology as well as the involved species. Metagenomic sequencing showed that only few different species were predominant in each sample type. However, the sinking properties remained useful for bioreactor application under all applied conditions. Despite the identification of methodological and technical challenges concerning the investigation of complex samples, this work provides new insights into the characteristics and internal drift of MBC cultures and their biotechnological potential in water treatment.