Effect of Strain-Specific Biofilm Properties on the Retention of Colloids in Saturated Porous Media under Conditions of Stormwater Biofiltration

Abstract

Filter performance can be affected by bacterial colonization of the filtration media, yet little is known about how naturally occurring bacteria modify the surface properties of filtration media to affect colloidal removal. We used sand columns and simulated stormwater conditions to study the retention of model colloidal particles, carboxyl-modified-latex (CML) beads, in porous media colonized by naturally occurring bacterial strains. Colloid retention varied substantially across identical columns colonized by different, in some cases closely related, bacterial strains in a cell density independent manner. Atomic force microscopy was applied to quantify the interaction energy between CML beads and each bacterial strain’s biofilm surface. We found interaction energy between CML and each strain was significantly different, with adhesive energies between the biofilm and CML, presumed to be associated with polymer-surface bonding, a better predictor of CML retention than other strain characteristics. Overall, the findings suggest that interactions with biopolymers in naturally occurring bacterial biofilms strongly influence colloid retention in porous media. This work highlights the need for more investigation into the role of biofilm microbial community composition on colloid removal in porous media to improve biofilter design and operation.

Influence of Simplified Microbial Community Biofilms on Bacterial Retention in Porous Media under Conditions of Stormwater Biofiltration

“…A substantial amount of variability in colloid retention in that study could be explained by strain-specific differences in adhesive forces between the biofilm and particle, measured by atomic force microscopy, which was assumed to be related to strain-specific surface characteristics such as the length and composition of biopolymers on biofilm surface ( 33 ). However, it is not clear if the findings are applicable to bacterial retention because of the differences in surface characteristics ( 33 – 35 ), shapes, and sizes between the model colloid and bacterial cells ( 36 ). Previous studies ( 37 , 38 ) have also demonstrated that biofilms formed by model laboratory strains, such as Pseudomonas aeruginosa PAO1 and PDO300, have different bacterial retention efficiencies, attributable to their variation in surface characteristics (e.g., biofilm surface charge, hydrophobicity, and biopolymer properties).…”

“…The variation in bacterial retention induced by biofilms might be attributable to the high variability in strain-specific characteristics of biofilm-forming bacteria, but the extent to which environmental bacteria can influence bacterial retention is unknown. Our previous study investigating the impact of biofilm formation by four bacterial strains isolated from stormwater on the retention of a model colloid (carboxyl-modified-latex beads) in porous media showed that interstrain variation in colloid retention efficiency was as high as 80% ( 33 ). A substantial amount of variability in colloid retention in that study could be explained by strain-specific differences in adhesive forces between the biofilm and particle, measured by atomic force microscopy, which was assumed to be related to strain-specific surface characteristics such as the length and composition of biopolymers on biofilm surface ( 33 ).…”

“…Our previous study investigating the impact of biofilm formation by four bacterial strains isolated from stormwater on the retention of a model colloid (carboxyl-modified-latex beads) in porous media showed that interstrain variation in colloid retention efficiency was as high as 80% ( 33 ). A substantial amount of variability in colloid retention in that study could be explained by strain-specific differences in adhesive forces between the biofilm and particle, measured by atomic force microscopy, which was assumed to be related to strain-specific surface characteristics such as the length and composition of biopolymers on biofilm surface ( 33 ). However, it is not clear if the findings are applicable to bacterial retention because of the differences in surface characteristics ( 33 – 35 ), shapes, and sizes between the model colloid and bacterial cells ( 36 ).…”

“…Hydrophobic biofilm surfaces remove water molecules from the surface and hence facilitate the adhesion to apolar surface sites of particulates ( 41 , 42 ). Additionally, long biopolymers protruding from biofilm surface might also extend beyond the range of electric-double-layer force and hence interact with particulates by themselves ( 33 , 37 , 40 ). However, because laboratory strains usually have a prolonged history of laboratory cultivation or genetically modified traits, it is not clear if the findings with laboratory strains can be applied broadly to environmental biofilms ( 43 – 45 ).…”

“…Biofilms in the environment are composed of complex microbial communities, but it is not clear how biofilm microbial community composition influences bacterial retention in filters. By testing the retention of various types of particles in single-strain biofilm-colonized filters, previous studies ( 27 , 33 , 38 , 46 , 47 ) have demonstrated that biofilms influence the retention of particles by covering and modifying porous media surfaces with their own specific surface characteristics. If the relative abundance of a population in a biofilm microbial community relates to the proportion of porous media surface area covered by that population, the impact of biofilms of complex microbial communities on bacterial retention will be closely related to the physicochemical characteristics of all constituent populations and their relative abundance.…”