Biofilm Effect on Capture and Retention of Colloids : Direct Observation and Analysis Using Microfluidics

Fate and transport of colloids such as pathogenic microorganisms and the processes affecting their transport behavior in subsurface environment is crucial to protect public health from waterborne diseases. Parameters like biofilm growth in aquatic environments can influence colloid transport and retention processes by modifying collector surface properties, porosity, and permeability of the media. In this study, microfluidic experiments using 1.5 μm fluorescent colloids were conducted to directly observe the impact of biofilm age/maturity on porous media properties, colloid removal, and transport mechanisms. Advanced fluorescent and confocal laser scanning microscopies together with image analysis provided accurate colloid trajectory data. Results demonstrated that as biofilm matured, media porosity and hydraulic conductivity decreased, while colloid removal efficiency and tortuosity increased. Biofilm development altered pore size distribution, created preferential flow paths, and contributed to different removal mechanisms like collision and straining. Micro scale experiments can help to understand removal mechanisms which can be used to interpret macroscale observations. While this study broadly investigated the impact of biofilms on colloid transport and removal, the primary focus was on the role of the bioactive layer, known as the Schmutzdecke, in functioning of slow sand filters