Study on the cleaning of new ultrafiltration spiral-wound modules to prevent membrane fouling (including biological fouling)

A study of cleaning a Bulgarian UF 60 PAN spiral-wound module was carried out on an ultrafiltration unit (Millipore, USA). Chemical cleaning of the membrane with a 0.25% solution of sodium metabisulfite did not prevent biological fouling. When treated with a 1% solution of formaldehyde, membrane fouling was diminished and the ultrafiltrate obtained contained a significantly lower number of microorganisms and colloid formations including iron and humic acids. After treatment with the two cleaning agents, the membrane maintained its flux for the water studied within a range of 1.58 to 1.64 m3/m2/d. The effect on the contaminants to be removed was also found to be comparatively constant. Membrane selectivity remained constant at different permeate yields.

The results obtained showed that, using a Bulgarian UF 60 PAN spiral-wound membrane module, up to 80% extraction of ultrafiltrate can be achieved. The chemical cleaning of this membrane with a 0.25% solution of sodium metabisulfite does not prevent biological fouling, and the total of microbial colonies of the permeate was higher than that of the feed water. When the membranes were regenerated with a 1.0% solution of formaldehyde, the biofouling was reduced and the content of humic acids in the permeate obtained was reduced about 60%, the total iron content up to 90% and content of microorganisms maintained a yield 80% below the requirements for drinking water (<100).