Nanoflotation – Using EDL Collapse to Increase the Efficiency of Flotation and Submerged Membrane Filtration

With most industrial water and wastewater treatment requirements, the objectives for
treatment are relatively consistent. Typically they are separation and removal of colloidal
particles, removal of free oil and grease and reduction in the parameters that either
cause scaling when water is reused or injected in disposal wells or have an effect when
released to the environment. We will review water treatment challenges for oil and metal
mining industries and provide a case study that deploys flotation followed by
ultrafiltration as a treatment solution. In this case study we demonstrate removal of
suspended and colloidal solids to 0.01 μm in size at efficiencies that are 10-times the
industry norm and at costs that make in-line treatment of tailings economically
achievable. The case study will be used to review the science behind microflocculation
through use of electric double layer (EDL) compression (the DLVO theory) and how this
can enhance traditional coagulation using charge neutralization. Colloidal solids, no
matter their charge, will repel each other because of the EDL on each solid. However
once the solid enters a highly ionized/charged environment, the EDL collapses and van
der waal attraction forces take over such that the solids attach to each other. Individual
charge on the solids, in both cases, has no bearing on whether a solid repels or attracts
one another. The use of microflocculation requires a novel design that can provide fixed
microzones of high ionic charge and a reliable mechanism to capture the small colloids
that are rapidly formed in these microzones; membrane treatment partially provides for
these needs. Loss of flux rates due to fouling, the nemesis of membrane treatment, had
to be solved to take advantage of microflocculation, a challenge overcome by the
Nanoflotation system reviewed in this case study. Solids removed from the water can
immediately be placed as reclamation fill as long as they pass soil criteria.