5.1 During the operation of a UF system, conditions including pressure and temperature can vary, causing permeate flow to change (see Note 1). To effectively evaluate system performance, it is necessary to compare permeate flow data at the same conditions. Since data may not always be obtained at the same conditions, it is necessary to convert the UF data obtained at actual conditions to a set of constant conditions, thereby standardizing the data. The user of this practice determines the standard conditions. This practice gives the procedure to standardize UF data on pure water only.

Note 1: Feed concentration, crossflow velocity, and both device and total system recovery will also influence permeate rate, especially when operating on other than pure water. This practice does not address those system conditions.

5.2 This practice can be used for systems which contain spiral-wound, tubular, plate and frame, and hollow fiber devices.

5.3 This practice can be used for a single-element or a multi-element system. However, if the UF system is staged, standardize the permeate flow and salt passage for each stage separately. This requires pressure readings at the feed inlet and concentrate outlet of each stage.

5.4 This practice is applicable for UF systems with no significant leaks between the feed/concentrate and permeate streams.

5.5 This practice assumes no significant osmotic pressure differential (Δπ) exists in the UF system under the actual operating conditions. Differential osmotic pressure will reduce the permeate rate relative to operation on pure water.

5.6 The user of this practice should be aware that fouled UF devices will produce less permeate flow than nonfouled devices, and may wish to perform flushing, chemical, or mechanical cleaning, or combination thereof, prior to determining the permeate flow performance of the device.