Functionalized polystyrene microspheres as Cryptosporidium surrogates.

Cryptosporidium, a waterborne protozoan pathogen that can cause gastrointestinal illness, is often found in surface waters that are used to supply drinking water. Filtration is a major process to remove Cryptosporidium in drinking water treatment. However, interactions between oocysts and filter media are still unclear and no satisfactory surrogates have been identified for quantifying their filtration removal in porous media. In the present study, polystyrene microsphere with a size, density, and shape similar to Cryptosporidium was modified with glycoprotein or synthesized biomolecules to mimic the surface properties of live Cryptosporidium oocyst. Deposition kinetics between live Cryptosporidium/modified microspheres and filter media were studied at the molecular scale using a quartz crystal microbalance with dissipation monitoring (QCM-D) and at the laboratory-scale using sand-packed columns. Both QCM-D and column experiments underlined the importance of Cryptosporidium surface charge and hydrophobicity on their attenuation and transport in porous media. As compared to live Cryptosporidium, glycopolymer and zwitterionic polymer co- odified polystyrene microspheres (later called copolymers-modified microspheres) represent comparable surface properties, adsorption kinetics on filter surfaces, and transport and deposition behaviors in filter columns; hence were selected as appropriate Cryptosporidium surrogates. This study improves our understanding on how surface characteristics impact Cryptosporidium transport behaviors in porous media and contributes to our capacity to evaluate the attenuation of Cryptosporidium in natural and engineered aquatic environments.