2 research outputs found
Colloidal Fouling of Ultrafiltration Membranes: Impact of Aggregate Structure and Size
A close coupling between the structure and size of hematite flocs formed in suspension and the
permeability of the cake that accumulates on ultrafiltration membranes is observed. Specific resistances of
cakes formed from flocs generated under diffusion limited aggregation (DLA) conditions are at least an
order of magnitude lower than cakes formed from flocs generated under reaction limited aggregation
(RLA) conditions. Similar effects are observed whether the aggregation regime is controlled by salt
concentration, pH or added organic anions. This dramatic difference in cake resistance is considered to
arise from the size and fractal properties of the hematite assemblages. The ease of fluid flow through these
assemblages will be influenced both by the fractal dimension of the aggregates and by their size relative to
primary particle size (since for fractal aggregates, porosity increases as the size of the aggregate
increases). The size and strength of aggregates are also important determinants of the relative effects of
permeation drag, shear induced diffusion and inertial lift and result, in the studies reported here, in
relatively similar rates of particle deposition for both rapidly and slowly formed aggregates. The results
presented here suggest that control of cake permeability (and mass) via control of aggregate size and
structure is an area with scope for further development though the nature and extent of compaction effects
in modifying the fractal properties of aggregates generated in suspension requires attention