Physicochemical and Hydrodynamic Effects on Colloidal Fouling Reduction inReverse Osmosis

摘要

An experimental study was carried out on colloidal fouling by iron hydroxide ofreverse osmosis membranes using tubular asymmetric cellulose acetate membranes. The study sought to determine whether there exists in turbulent flow a threshold transmembrane (permeation) velocity below which no colloidal fouling takes place. Experiment established and a simple model confirmed that under stable colloid conditions, where the colloid does not floc or aggregate, that there does exist a threshold velocity in turbulent flow whose value is about the same as in laminar flow. Under unstable conditions, where electrolytes are present, a threshold velocity still exists but its value is greatly reduced. The threshold velocity phenomenon can be used in practice to reduce or eliminate colloid fouling for stable solutions, although it is not useful where electrolytes are present, as in seawater. Importantly it is found that there is no advantage to employing turbulent flow to reduce fouling when operating at threshold conditions, as the threshold velocity value was found to be independent of the axial flow Reynolds number up to a value of 26,300.