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1.1 This test method covers the determination of the modified fouling index (MFI) of water measured at constant pressure. This test can be used to indicate the fouling potential of reverse osmosis/nanofiltration (RO/NF) feed water due particulate matter and is applicable to low and high turbidity waters. Since the size, shape, and nature of particulate matter in water may vary, this test method is not an absolute measurement of the quantity of particulate matter.

1.2 This test method is not applicable for reagent-grade water Types I, II, and III of Specification D1193 or effluents from most reverse osmosis and ultra-filtration systems.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 This test method is an alternative for the silt density index (SDI) method (Test Method D4189) with the aim to overcome inaccuracies related to a nonlinear relation with the fouling potential due to particulate matter concentration, absence of temperature correction, support pad, and time.

5.2 The MFI-0.45 can serve as a useful indication of the quantity of particulate matter.

5.3 The MFI-0.45 can be used to determine effectiveness of various processes such as filtration or clarification used to remove particulate matter.

5.4 The MFI-0.45 has empirically been correlated with fouling tendency of some water treatment equipment such as reverse osmosis (RO) devices.