Modified fouling index

Fifty years ago, the SDI test was developed to predict the fouling tendency for the DuPont Permasep Permeators (hollow fine fiber RO elements). The SDI test is still the standard method for fouling prediction on spiral 

A test method called the modified fouling index (MFI or MFI-0.45) is gaining popularity and has been used in Europe for 25 years. The test was developed based on Darcy s Taw that relates flux (dV/dt) to the thickness of the cake layer, which is the sum of the filter resistance (R ) and the cake resistance (R)  

V = total volume produced AP = transmembrane pressure p = dynamic viscosity of water A = membrane area 

These equations predict a linear relationship between t/V and V during cake formation. 

One difficulty with the MFI is that it uses a 0.45 MF membrane, which allows smaller colloidal particles to pass that foul RO or NF membranes. Thus, researchers have proposed an MFI-UF test that uses ultrafiltration (UF) membranes rather than the MF membranes. The UF membranes have an order of magnitude smaller pore side and can capture more of the smaller colloids. 

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Schippers, J.C. and Verdouw, J. 1980. The modified fouling index, a method of determining the fouling characteristics of water. Desalination 32, 137-148. 

INVESTIGATION OF THE RELATIONSHIP BETWEEN PLANKTON COUNTS, PARTICLE COUNTS, AND MODIFIED FOULING INDEX... 

Schippers and Verdouw [ 4 ] developed the technique of modified fouling index in order to assess fouling properties of water to be treated by reverse osmosis. 

No strict relationship existed between algae counts and the modified fouling index (MFI) as developed by Schippers et al. [ 6 ]. Nevertheless, results obtained showed that the MFI may give valuable information on rapid filtration efficiency of removal of net phytoplankton. Optimization of the coagulation process may be possible by using treshold values. Additional work however is needed to... 

Boerlage S.F.E., Kennedy M.D., Bonne P.A.C., Galjaard G., Schippers J.C. (1997), Modified fouling index for the prediction of the rate of flux decline in reverse osmosis, nano- and ultrafiltration systems, Proc. AWWA Membrane Technology Conference, New Orleans, Feb. 97, 979-999. 

Attempts to quantify the fouling propensity of a feed water such as the Silt Density Index (SDI) and Modified Fouling Index (MFI) have met with limited success [128] due to the complex interactions between membrane and foulant. Fouling by natural organic matter depends critically on solution pH, ionic strength, and the presence of divalent cations due to changes in macromolecular structure [129]. Techniques for monitoring biofilm and scale formation are summarized in the literature [130]. 

The ASTM is currently working on WK45948, New Test Method for Modified Fouling Index (MFI-0.45) of Water, to develop a companion procedure to the SDI for more accurate prediction of membrane fouling. Although there are devices on the market that automatically or semi-automatically measure both SDI and MFI-0.45, the MFI still has the following issues that need to be resolved ... 

Siobhan EE. Boerlage, Maria D Kennedy, Melvyn R. Dickson, Dima E.Y. El-Hodali, and Jan C. Schippers, The Modified Fouling Index using Ultrafiltration Membranes (MFI-UF) Characterisation, Filtration Mechanisms, and Proposed Reference Membrane, Journal of Membrane Science, 197, 2002. 

ASTM, New Test Method for Modified Fouling Index (MFI-0.45) of Water, ASTM WK45948. 

In order to measure the particulate fouling potential of feed water, Schippers and Verdouw [48] proposed a modified fouling index (MFI) by using a microfiltration membrane as a quick test of the feed water quality. They further improved the accuracy of the index and developed a new index of MFI-UF by using ultrafiltration membranes to increase the index sensitivity to the presence of colloidal particles for constant pressure operation [49, 50] and constant flux operation [51]. 

Khirani, S., R. B. Aim, and M.-H. Manero. 2006. Improving the measurement of the Modified Fouling Index using nanofiltration membranes (NF-MFI). Desalination 191 1-7. 

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