Effect of powdered activated carbon on immersed hollow fiber ultrafiltration membrane fouling caused by particles and natural organic matter

Membrane fouling is one of the primary concerns on ultrafiltration (UF) application in drinking water treatment. There is a dispute about whether or not powdered activated carbon (PAC) addition is able to alleviate the membrane fouling. This investigation was conducted to further understand the effect of PAC addition on UF membrane fouling. Immersed polyvinylidene fluoride (PVDF) hollow fiber membrane was utilized in the experiment. Kaolinite and humic acid (HA) were added in tap water to simulate the particles and natural organic matters (NOM) in raw water. The results verified that PAC addition could mitigate the total membrane fouling effectively by HA, while has little effectiveness on that by kaolinite and HA-kaolinite. This effect was attributed to the enhancement of organic matter removal and the reduction in irreversible fouling by HA in PAC-UF process. Results of molecular weight (MW) distribution and XAD fractionation indicated that PAC addition was mainly responsible for the removal of HPI fraction and organic matters with MW lower than 1 kDa. SEM images illustrated that the PAC cake layer on the membrane surface partially protects NOM from adsorption into the membrane pores, decreasing irreversible membrane fouling and resulting in significantly higher membrane specific flux recovery by water backwashing. But the PAC-contained cake layer increases the reversible resistance. Batch dosing was recommended for its simplicity and higher effectiveness over continuous dosing.