Rotating algal biofilm reactors retain core microbial communities during scale-up.

backgroundMicroalgae-bacteria biofilm reactors are a promising alternative to conventional wastewater treatment because they can simultaneously remove nitrogen and phosphorus while producing harvestable biomass. Rotating algal biofilm reactors (RABRs) implement this concept by growing attached microalgae–bacteria biofilms on rotating surfaces that alternately contact wastewater and air, which can enhance nutrient uptake and simplify harvesting. However, successful field implementation requires that biological performance observed at lab scale translate to larger systems. Few studies have examined whether microbial community structure is conserved during scale-up. Here, using RABRs as a case study, we tested whether biofilm community composition is preserved during scale-up when all systems are seeded from a common trickling-filter biofilm inoculum.

resultsAcross scales, 16S profiles consistently showed dominance by Proteobacteria and Bacteroidetes, supporting preservation of a core bacterial community. Phototrophic communities (23S) were similarly conserved, with Chlorophyta and Cyanobacteria co-dominant across systems. In contrast, the 18S profiles showed greater variability, with the trickling filter strongly dominated by Opisthokonta, while the pilot-scale system exhibited substantial enrichment of Alveolata. Alpha-diversity patterns indicated that lab-scale reactors supported simpler communities than the trickling filter and pilot system.

conclusionRABR scale-up preserved dominant bacterial and phototrophic taxa when reactors were seeded from a common stable-composition trickling-filter inoculum, while eukaryotic communities showed greater sensitivity to operating context and outdoor exposure. These findings support inoculum sourcing and microbial community profiling as practical tools for scalable RABR design and process evaluation.