Colloidal particles, such as pathogens or microplastics, contaminate urban stormwater runoff, prevent non-potable reuse and threaten public health. Engineered infiltration systems (EIS) designed with sand media are one of the most popular green infrastructure technologies used to treat stormwater. EIS deployed in the field have variable efficiencies in removing colloidal particles, potentially due to variable characteristics of biofilms fouling the sand media surface during normal operation. Little is known about how surface properties and total biomass of the biofilm within the EIS affects colloidal removal. The present study investigates the impact of biofilms of four bacterial species isolated from EIS and a model biofilm forming isolate (<i>Pseudomonas aeruginosa)</i> on the retention of a model colloidal particle, carboxyl-modified-latex beads (CML), in EIS sand columns. Comparing to the retention of CML in clean bed sand columns (attachment efficiency (alpha) = 0.56), all four EIS isolates inhibited CML retention (alpha ranges from 0.02 to 0.39), while <i>P. aeruginosa </i>biofilm enhanced retention (alpha = 1.05). Varying the amount of biomass of each isolate in the column did not explain strain-specific variation in CML retention. To determine how surface properties of the biofilm affect CML retention, repulsive energy upon approach, adhesive force during separation after contact and indentation length to determine biofilm thickness was measured with atomic force microscopy (AFM). The results demonstrate that each isolate has unique surface profiles, even given extensive measurement heterogeneity. Many isolates had high adhesion and repulsion presenting at low indentation length, suggesting that extra-cellular polymeric substances influences repulsive and adhesive characteristics of biofilm. The adhesive force is likely to be induced by the stretching of polymers on biofilm that formed bonds with CML bead surface during contact, as suggested by the force-distance curves. The retention of CML by biofilms cannot be explained by a simple combination of repulsive and adhesive forces. However, the data suggest alpha is related to adhesion between biofilm and CML after contact but larger repulsive forces prevent contact. This is the first study that investigated the impact of colloid-biofilm interfacial force and biomass on colloidal retention in EIS fouled with natural isolates.

Impact of biofouling on the retention of stormwater colloidal contaminants in engineered infiltration system (EIS)

2019 Fall National Meeting

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