Distinct interactions of pig and cow manure-derived colloids with TiO2 nanoparticles and their impact on stability and transport

The application of livestock manure and aquaculture wastewater into agricultural soil introduces animal manurederived colloids into the environment. These manure-derived colloids generally contain different organic matter components and may facilitate nanoparticle transport to the subsurface. This study investigated the interaction between manure-derived colloids (cow and pig manures) and titanium dioxide (TiO2) nanoparticles at neutral pH. The effect of this interaction on the stability, aggregation, and transport of TiO2 in a saturated porous media was studied. Our study found that cow manure-derived colloids have many humic-like substances, and pig manure-derived colloids contain many protein components and some humic-like substances. The interactions of different manure-derived colloids with TiO2 can affect the zeta-potential and aggregation status of TiO2 in the aqueous system. The results showed that cow manure-derived colloids slightly increased the TiO2 transport due to electrostatic repulsion, while pig manure-derived colloids substantially increased the TiO2 mobility in porous media because of both electrostatic repulsion and steric hindrance. Since both animal manure and TiO2 are ubiquitously present in the natural environment, manure-derived colloids can change the surface properties of TiO2 and facilitate TiO2 transport in the subsurface.