Lab and pilot scale investigations on membrane fouling during the ultrafiltration of surface water

In the combined laboratory and pilot plant investigation powder activated carbon dosing and inline coagulation were investigated for surface water from river Spree. The aim was to understand the fouling behaviour of this raw water and to understand and to identify strategies to minimize the irreversible fouling in this application. Trials with activated carbon showed significant differences in the adsorption of biopolymers on different types of carbon. Whereas the TOC removal was in the same range for both types the coarse carbon type showed very small removal of biopolymers. The effect of different types of coagulants, dosage and pH was investigated in a laboratory filtration set up. Samples were investigated by LC-OCD measurements for fractionation of DOC for raw water, flocculated water and permeate. The removal of biopolymers was possible with iron and alumina salts, however the alumina salts tend to remove humic acids as well and this results in a higher overall DOC removal. In the pilot plant the inline coagulation was investigated under actual site conditions. Whereas the results for the effect of coagulation and DOC removal were confirmed it turned out that aluminium coagulants give a significantly higher increase in differential pressure. The use of ferric coagulants at slightly acidic pH was thus identified as a robust method to achieve a stable performance of the ultrafiltration system at this site.