Fouling Indices for Quantification of Natural Organic Matter Fouling and Cleaning in Ceramic and Polymeric Membrane Systems

A key challenge in membrane system is to understand how operating pressure and water temperature may impact fouling and subsequent cleaning in relationship to NOM. Further there is limited data to ascertain if ultrafiltration (UF) polymeric and ceramic systems will respond in similar or different manners to NOM fouling which then further impacts how respective systems need to be cleaned. This research investigated the application of the MFI-UF in complement with the UMFI for assessing NOM fouling and cleaning under changes in filtration conditions with both ceramic and polymeric membranes systems. The research showed that all NOM types exhibited higher MFI-UF values, and therefore, higher fouling propensity as pressure increased from 1 to 3 bars and water temperature decreased from 35°C to 5°C indicating the effect of pressure and temperature on the MFI-UF fouling prediction. The NOM fouling potential order was consistent at different temperature which was the highest for the NOM mixture and proteins (BSA) followed by alginate and lastly humic acid. Variation in feed water temperature in polymeric and ceramic membrane systems demonstrated negative impacts on NOM fouling and cleaning. NOM fouling increased as water temperature decreased from 20°C to 5°C while fouling decreased as temperature increased from 20°C to 35°C. The UMFI analysis showed that irreversible NOM fouling ratios increased at cold water condition (5 °C), along with decreased in backwash and chemical cleaning effectiveness of both membrane types. The UMFI results obtained in the polymeric and ceramic UF systems demonstrated useful fit with the MFI-UF prediction for establishing NOM fouling trend and order with temperature. Under an equivalent fouling and cleaning conditions, NOM fouling order of a ceramic UF membrane was found to be similar to their polymeric counterparts. However, the ceramic UF demonstrated better performance in terms of backwashing, thus, lower irreversible fouling. Chemical cleaning of a ceramic UF membrane using O3 CIP for 1 hour at a ratio of 0.50 mgO3/mgC demonstrated higher reduction of irreversible fouling of hydrophobic and hydrophilic NOM fractions and lower sensitivity to water quality conditions compared to 4 hours cleaning using combined NaOCl and NaOH CIP.