The Modified Fouling Index Ultrafiltration constant flux for assessing particulate/colloidal fouling of RO systems

Abstract

A safe MFI value has been defined for RO feed water.• A new portable set-up can perform MFI-UF tests at constant flux filtration.• Low filtration flux and membrane pore size are important variables in the test.• The MFI-UF constant flux can assess pre-treatment of RO systems.• Measuring the deposition factor is important to estimate the rate of RO fouling. a b s t r a c tReliable methods for measuring and predicting the fouling potential of reverse osmosis (RO) feed water are important in preventing and diagnosing fouling at the design stage, and for monitoring pre-treatment performance during plant operation. The Modified Fouling Index Ultrafiltration (MFI-UF) constant flux is a significant development with respect to assessing the fouling potential of RO feed water. This research investigates (1) the variables influencing the MFI-UF test at constant flux filtration (membrane pore size, membrane material, flux rate); and (2) the application of MFI-UF into pre-treatment assessment and RO fouling estimation. The dependency of MFI on flux, means that to assess accurately particulate fouling in RO systems, the MFI should be measured at a flux similar to a RO system (close to 20 L/m 2 /h) or extrapolated from higher fluxes. The two studied membrane materials showed reproducible results; 10% for PES membranes and 6.3% for RC membranes. Deposition factors (amount of particles that remain on the surface of membrane) were measured in a full-scale plant ranging between 0.2 and 0.5. The concept of "safe MFI" is presented as a guideline for assessing pre-treatment for RO systems.

Recovery, overloading, and protein interactions in asymmetrical flow field-flow fractionation

“…The recovery was similar for all the protein standards, but it should be noted that the proteins were analyzed in a carrier liquid of physiological ionic strength (PBS 0.15 M) and at a pH (7.2) higher than the pI values of the proteins (Table 1 ) and of the membranes [ 47 , 48 ]. Previous studies showed that at low ionic strength conditions (which favor electrostatic interactions) significant adsorption may occur when the solutes have a charge opposite to that of the membrane [ 49 ] or when the pH is close to their isoelectric point [ 14 ].…”

“…These findings are consistent with those of previous studies that showed higher adsorption of biomolecules on PES membranes in AF4 [ 15 , 50 ]. Salinas-Rodriguez et al [ 47 ] and Alele et al [ 48 ] compared the properties of ultrafiltration RC and PES membranes and concluded that both are hydrophilic (contact angle < 90°) but that RC is more hydrophilic than PES. PES membranes have a high degree of hydrophobicity because of the aromatic groups but they are often chemically or physically modified in order to become more hydrophilic [ 51 ].…”

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 membrane filtration, membrane fouling is a critical problem leading to the degradation of ultrafiltration performance and causes a dramatic flux decline during the process due to a significant increase in the filtration resistance. There exist several factors affecting membrane fouling, for example, cake formation, [1][2][3][4][5][6][7][8] pore blocking and/or pore constriction, 9,10 solute adsorption, 11,12 and concentration polarization. 13,14 Among them, the impact of the filter cake on the flux decline behavior in ultrafiltration is still not fully understood in spite of its importance.…”