Natural and engineered filtration can be very effective at removing colloids, nanoparticles, and waterborne pathogens from water. Classic filtration theory was developed based on numerical solutions from Convective-Diffusion models or trajectory analysis when 1) particle and collector surfaces are oppositely charged with no interaction energy barrier and 2) both contact surfaces are smooth. However, in most environmental systems, surface roughness is generally present on collector surfaces and depositing particles and collectors are negatively charged. Not surprisingly, significant discrepancies between theoretical predictions and experimental observations have been commonly reported when surface roughness is present on collector surfaces.<br/><br/>Here, bench-scale experiments were conducted to assess the impacts of collector roughness on particle deposition in a packed column at favorable and unfavorable conditions for particle deposition at a variety of ionic strengths. Two sizes of fluorescent microspheres, two sizes of glass beads, four environmentally relevant levels of suspension fluid ionic strength, and three levels of surface roughness were utilized. These suspensions were fed into the columns at a loading rate of 1.5 m/h. Normalized column effluent concentrations, retained particle distribution profiles, and total mass recovery ratios were utilized to evaluate the impacts of media/collector surface roughness on particle deposition in packed media.<br/><br/>This work systematically demonstrates that collector surface roughness consistently influences particle deposition in a non-linear, non-monotonic manner, irrespective of the presence of an energy barrier. Critically, the differences in particle deposition that were observed on media with different levels of collector surface roughness could not be solely explained by ionic strength-associated changes in DLVO interaction energy. Moreover, surface roughness and ionic strength concurrently affected particle deposition in a manner that is not simply additive. The secondary energy minimum alone appeared inadequate for explaining the observed particle deposition behavior, however, particle deposition rates were highly correlated with inverse Debye-Hückel length using second-order polynomial functions. These relationships may provide insight for further development of physico-chemical filtration models for describing particle deposition on surfaces.

Advancing filtration theory: Concurrent contributions of media surface roughness and ionic strength on particle deposition

255th National Meeting (2018)

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