Microfiber-flocked surfaces as a novel platform for biofilm and biohydrogen production.

For biohydrogen production, immobilized systems offer the potential for improved growth and productivity. In this study, microfiber-flocked surfaces were used as a novel strategy for Rhodobacter capsulatus biofilm-based photofermentative biohydrogen production. The surfaces were developed using electrostatic flocking by attaching polyamide microfibers to glass and poly methyl methacrylate (PMMA) surfaces. Parameters such as fiber length, density, and adhesive type were optimized to develop shorter, denser, and vertically oriented microfiber structures. This optimized architecture increased the available surface area for bacterial attachment and biofilm formation while maintaining sufficient light transmittance through the flocked layer. The combination of enhanced biofilm development and adequate light availability supported photosynthetic activity, resulting in enhanced cell growth and hydrogen production. For anaerobic cultures, inclined (vertical) photobioreactor provided superior attachment compared to horizontal setups, presumably due to better light exposure and nutrient availability. These enhanced surfaces led to increased cumulative hydrogen production over 21 days during repeated-batch operations with Rhodobacter capsulatus in a novel photobioreactor. This resulted in a stable biofilm (Abs590: 0.65 ± 0.04) and a hydrogen productivity of 0.32 ± 0.05 mmol/L.h. Thick biofilms formed on the microfiber flocks, exhibiting interconnected extracellular matrices and filamentous extracellular structures. In contrast, horizontally oriented surfaces and aerobic conditions were less effective, as sub-optimal light and oxygen atmosphere levels appear to hinder biofilm growth and hydrogen output. Additionally, a combined ultrasonication and Tween surfactant treatment enabled efficient cell removal and biomass recovery, suggesting reusability of the engineered surfaces. These results highlight microfiber-flocked surfaces as a potential platform for enhanced microbial growth and biohydrogen production. The proposed strategy contributes to the development of biofilm-based continuous processes.