Enhanced retention of bacteria by TiO2 nanoparticles in saturated porous media

• Bacterial transport in groundwater was affected by TiO2.
• Retention of bacteria and TiO2 nanoparticles was enhanced when both are present.
• Heteroaggregation and electrostatic interactions controlled the deposition and retention.
• TiO2 attachment to the sand was explained by electrostatic forces. TiO2 acted as bond between bacteria and sand.
• DLVO and classical filtration theories were used to model the interactions between particles and between particles and sand.

The simultaneous transport of TiO2 nanoparticles and bacteria Pseudomonas aeruginosa in saturated porous media was investigated. Nanoparticle and bacterium size and surface charge were measured as a function of electrolyte concentration. Sand column breakthrough curves were obtained for single and combined suspensions, at four different ionic strengths. DLVO and classical filtration theories were employed to model the interactions between particles and between particles and sand grains. Attachment of TiO2 to the sand was explained by electrostatic forces and these nanoparticles acted as bonds between the bacteria and the sand, leading to retention. Presence of TiO2 significantly increased the retention of bacteria in the sand bed, but microorganisms were released when nanomaterial influx ceased. The inclusion of nanomaterials in saturated porous media may have implications for the design and operation of sand filters in water treatment.