Understanding and Control of Biopolymer Fouling in Ultrafiltration of Different Water Types

The present work focuses on understanding and control of biopolymer fouling in ultrafiltration of a typical surface water and nearby secondary effluent for direct and indirect portable use. Characterization results show that both kinds of biopolymers are of similar molecular weight. Longer than one year water quality monitoring results show that the C/N ratio in the secondary effluent biopolymers was relatively constant at around 4.8, while that in the surface water macromolecules fluctuated at around 6.9. Under a similar mass load, the investigated secondary effluent biopolymers lead to hydraulic resistance slightly higher than that caused by filtering surface water macromolecules; however, the correspondingly formed fouling is significantly less reversible by hydraulic backwashing. The quantity of the nitrogenous biopolymers in the secondary effluent demonstrated a strong correlation with the extent of the irreversible fouling in ultrafiltration (UF), while that from the surface water did not. In membrane fouling cleaning tests, certain detergent demonstrated high efficiency in removing the irreversible fouling after UF of the secondary effluent, but presented no effect in eliminating fouling caused by the surface water foulants. In-line coagulation using FeCl3 prior to UF was shown as an effective fouling control method, but the effect depends heavily on the type of feed water.