Evaluation of PAC behavior and fouling formation in an integrated PAC–UF membrane for surface water treatment

This study was conducted to understand fouling formation and effect of PAC addition in a hollow-fiber ultrafiltration membrane integrated with adsorption. Daily carbon accumulation rate and carbon mass load to UF module were estimated to be about 10 mg/L and 117 g/m2·d, respectively, however carbon build-up within the PAC–UF membrane was not so significant during 76 days operation and was locally limited to inlet and outlet of module, which were vertical to direction of linear velocity. Carbon addition had scouring effect on large particles and could prevent particles larger than 6 µm from depositing on the hollow fibers. Organic amount extracted from the PAC–UF was almost half that from the UF, due to reduction of organic load by carbon adsorption. PAC addition also imparted an entrapping effect on metal ions within PAC, however PAC remained from incomplete backwash increased amount of inorganic foulant extracted from the PAC–UF. Reversible resistance by particles and carbons was the greatest by 54% of total reversible resistance, followed by inorganic (33%) and organic foulants (13%). More deliberate strategies such as sufficient backwashing pressure, greater linear velocity, feed water direction and module design can be expected to alleviate cake formation through this investigation.

Carbon behavior in the PAC–UF membrane was investigated by continuous turbidity and particle measurements of feed water, carbon treated water and circulated water. PAC accumulation rate could be estimated by 10 mg/L·d per hollow-fiber module and carbon load to the membrane surface, by 117 g/m2·d. However the carbon build-up was not so significant for this operation period and localized mainly in the inlet and outlet parts of the module, which were perpendicular to the direction of linear velocity and zone of stagnant flow. Added carbon provided scouring effect on large particles from the membrane module, resulting in a decrease of their deposit in the hollow fibers. Organic foulant amount extracted from the PAC– UF membrane was significantly lower than that from the UF membrane (almost less than half), due to carbon adsorption of the organic foulant before the PAC–UF membrane. PAC addition played a role to entrap metal ions within PAC, however PAC remained even after backwash and extracted amount of inorganic foulant from the PAC–UF membrane increased. Particle resistance caused by carbons and natural particles could be recovered by physical cleaning up to 54% of total reversible resistance, and more reversible resistances composed of inorganic matter (33%) and organic matters (13%). Finally, the increase of backwashing pressure, greater linear velocity, system design such as feed water direction and proper module design will be required to be deliberated suitable for this integrated PAC–UF membrane.