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

Abstract

Polymeric membranes have emerged as an economically effective treatment option to produce drinking water. More recently, ceramic membranes are raising interest in this field due to their unique physical properties, which may prove to be important in moving towards more robust and sustainable drinking water treatment methods. However, the loss of membrane permeability as a result of natural organic matter (NOM) fouling remains one of the biggest challenges for sustainable polymeric and ceramic membranes operation. 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.Fouling indices have been developed by means of simple, short, empirical filtration tests to assess the fouling potential of membrane feed water. The modified ultrafiltration fouling index (MFI-UF) is a standard test that is used to estimate a fouling index value that gives a general indication about the treatability of feed water or the need for pretreatment prior to a membrane unit. Unlike the MFI-UF, the unified membrane fouling index (UMFI) is used to quantify fouling a membrane is subjected to (i.e. reversible vs. irreversible), which provide different data on fouling. However, different approaches in fouling assessment may suggest that direct comparison lack context which lead to some disconnect between predicted and actual fouling in the field. Thus, the applicability of the MFI-UF to be effectively used in complement with the UMFI to predict NOM fouling under changes in iii filtration conditions needs to be examined with both ceramic and polymeric membranes systems.In addition, due to the superior chemical resistance of ceramic membranes, the utilization of high cleaning pH 12 solutions in a single, stepwise, or combined approach with sodium hypochlorite (NaOCl) and sodium hydroxide (NaOH) and ozone (O3) clean in place (CIP), which are not recommended with polymeric membranes, could highlight an advantage to ceramic membranes in drinking water applications for irreversible NOM fouling control.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. The MFI-UF normalization model was useful in estimating the fouling potential away from standard testing conditions (2 bar and 20°C). Therefore, MFI-UF values measured at standard testing conditions can be altered to actual filtration conditions by adjusting for the pressur...