A Biosorption Study of Triclosan and Benzalkonium Chloride: Exploring the Role of Biofilm and Soil Grain Surface Chemistry in Drainfields

Although sorption is crucial for removing contaminants
of emerging
concern (CECs) in on-site wastewater treatment systems (OWTS), and
biofilms develop extensively within drainfields, little is known about
the effects of sorption and biosorption (with biofilm) on contaminant
fate. To gain insights, the transport of triclosan (TCS) and benzalkonium
chloride (BAC) (hydrophobic and amphiphilic antimicrobials, respectively)
was studied in saturated sand columns with and without 1-day-old and
3-day-old biofilms. Triclosan S-shaped breakthrough curves (BTCs)
indicated cooperative sorption, and BAC two-step BTCs suggested irreversible
sorption with a maximum capacity. One-day-old biofilms increased TCS
retardation while showing no effect for BAC. The 3-day-old biofilms
further increased TCS retardation and decreased BAC retardation. Therefore,
early stage biofilms can affect contaminant sorption in as little
as 1 day and add new TCS sorption sites, whereas hindering BAC sorption.
Quartz crystal microbalance with dissipation (QCM-D) using SiO2 and Fe2O3 sensors showed higher protein
deposition than humic acids and polysaccharides at pH 7, suggesting
that proteins drive extracellular polymeric substance (EPS) deposition.
Higher BAC deposition on the clean SiO2 sensor than on
the EPS-coated sensor revealed that EPS likely impaired BAC electrostatic
interactions with the surface. These findings support that biofilms
affect contaminant mobility and highlight the need for considering
biosorption in optimizing OWTS design.