| Colloid filtration experiments were performed using latex particles (50 nm, 110 nm and 1500 nm) in both the presence and absence of 5.0 mg/L humic acid (HAs). At low ionic strengths (1 -- 10 mM KCl), an increase in attachment efficiency (alpha) with increasing particle size was observed, which contrasts with predictions based on DLVO theory. The presence of HAs generally resulted in a decrease in alpha. Characterization experiments to better understand this behaviour included particle sizing using dynamic light scattering (DLS) and zeta potential using laser Doppler velocimetry (LDV). The particles' hydrodynamic diameters were unchanged in the presence of HAs. HAs lead to an increase in absolute zeta potential for the 50 nm and 110 nm colloids and a decrease in zeta potential for the 1500 nm particles. A discussion of the apparent deviations from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and explanations for the observed behaviour are provided. |
