Macroscopic and microscopic characterizations of a cellulosic ultrafiltration (UF) membrane fouled by a humic acid cake deposit: First step for intensification of reverse osmosis (RO) pre-treatments

Abstract

One of the critical issues for the application of low-pressure membrane processes (microfiltration, MF or ultrafiltration, UF) as pre-treatment processes for freshwater preparation is membrane fouling due to natural organic matter (NOM). The aim of this preliminary study is to contribute to a better understanding of the fouling phenomena occurring on a regenerated cellulose UF membrane fouled with a humic acid cake deposit. The originality of this work is based on a double approach on surface analysis at both macroscopic and microscopic scales. It is presently reported that humic acid fouling is mainly governed by cake formation, which plays a major role in flux decline via the well-known model of resistances in series. We obtained that the adsorbed resistance is 2% of the total resistance while the cake resistance is 52% of the total resistance, which is higher than that of the virgin membrane. From field emission gun scanning electron microscopy (FESEM) it was found for the first time that the humic acid cake is well organized, and particularly in fractal forms. The fractal dimension (FD) of the cake is determined as 2.52, which is in good agreement with the theoretical fractal dimension of particleecluster aggregation underlying diffusion-limited aggregation (FD ¼ 2.51). This new microscopic fouling index decreases with the presence of cake and can be correlated with the decrease of the hydraulic permeability. The classical silt density index (SDI) and the new modified fouling index (denoted MFI-UF) were obtained and also proved the presence of the cake. To complete this approach transmembrane streaming potential (denoted SP) measurements were conducted with a new homemade apparatus developed in our lab and presented for the first time in the present article, helped us to observe also a penetration of low molecular fractions of humic acid inside the membrane. Indeed the displacement of the isoelectric point (iep) of the membrane from 2.3 to 1.5 for the virgin and fouled membranes, respectively, permitted to illustrate this penetration. This newly designed SP apparatus is a semi-automatic tool assisted by a software denoted as proFluid 1.2. Furthermore, preliminary

Effect of surface morphology on membrane fouling by humic acid with the use of cellulose acetate butyrate hollow fiber membranes

“…Humic acid is a fraction of humic substances composed of a long chain molecule, which is high in molecular weight, dark brown in color and soluble in an alkaline solution. According to a lot of publications, membrane fouling by humic substances is influenced by the characteristics of humic substances, the hydrodynamic conditions, the chemical composition of the feed water and the properties of membranes [12,13]. Understanding of these factors is essential for better control of membrane fouling.…”

Developments of Blocking Filtration Model in Membrane Filtration

“…While membrane filtration is a key process which has the widespread application, it is generally recognized that one of the major drawbacks to more widespread use of membrane filtration is a significant increase in the filtration resistance known as membrane fouling, resulting in a dramatic flux decline over time under constant pressure conditions or a remarkable pressure rise over time under constant rate conditions. The membrane fouling is affected by several factors, e.g., pore blocking and/or pore constriction Bredée, 1935, 1936;Grace, 1956;Shirato et al, 1979;Hermia, 1982;Iritani et al, 1992Iritani et al, , 2009Iritani et al, , 2013, cake formation (Reihanian et al, 1983;Chudacek and Fane, 1984;Iritani et al, 1991aIritani et al, , 2014aNakakura et al, 1997;Mohammadi et al, 2005;Thekkedath et al, 2007;Sarkar, 2013;Salinas-Rodriguez et al, 2015), solute adsorption (Fane et al, 1983;Iritani et al, 1994), and concentration polarization (Kimura and Sourirajan, 1967;Vilker et al, 1981). Initially, foulants smaller than the pore size of membrane deposit or adsorb onto the pore walls, thereby leading to the pore constriction.…”

Nanocolloid cake properties determined from step‐up pressure filtration with single‐stage reduction in filtration area

“…In Eq. 4, the pressure drop Dp c across the filter cake is described by Dp c 5p2Dp m 5p2lR m u 1 (6) With the aid of Eq. 6, Eq.…”