Revisiting the Microscopic Processes of Biofilm Formation on Organic Carriers: A Study under Variational Shear Stresses.

The microscopic process of biofilm development on carriers is critical for interfacial regulation of biofilms in attached-growth wastewater treatment. However, the process under shear stress has not been well understood. The study purposed to revisit the processes of biofilm formation on organic carriers under different shear stresses with special highlights on bacterial reversible adhesion and pioneers in the microbial community. Biofilm formation on high-density polyethylene, polyamide, acrylonitrile butadiene styrene plastic, polyvinyl chloride, and polycarbonate carriers under shear stresses ranging from 1.0 to 2.5 Pa was investigated using Couette-Taylor reactors. Employing extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the bacterial reversible adhesion regions ranging from 3.74 ± 0.20 to 5.51 ± 0.24 nm on an organic carrier were quantified for the first time, elucidating significant differences among different carriers ( p < 0.01). The colonization of pioneers in the microbial community was significantly altered by shear stress rather than carrier properties ( p < 0.01). In particular, the diversity of the biofilm microbial community was pronouncedly enhanced by a higher shear stress ( p < 0.01). XDLVO analysis suggested that extracellular polymeric substances had a negative feedback on subsequent microbial adhesion and biofilm development, especially the transition from reversible to irreversible bacterial adhesion. This study contributed to a better understanding of the biofilm formation process at the microscopic scale and shed light on micro-interfacial manipulation for biofilm accumulation or renewal.