EC Container 5
UF modules are designed with high circulation velocities up to 18 feet/second to create a turbulent flow, which minimizes the build up of solids on the membrane surface. Individual modules may be arranged in parallel or in series. A combination of both is also possible. Parallel configurations have the lowest pressure drop, the highest flux, and the highest transmembrane pressure (TMP). Additional recirculation flows result in a pressure drop in each module and an increase in energy requirements. Series arrangements decrease TMP in subsequent elements, resulting in a reduced flow. Even though the feed pumps are smaller in a series arrangement, more modules are required.
UF membranes require only a coarse pretreatment to improve its filterability. This benefit is realized as a result of the flow channels in A3's UF tubular membranes. Narrow-flow-channel flat sheet (spiral wound) or small diameter capillary membranes (hollow fiber) require a more thorough pretreatment. Additionally, using a ceramic membrane offers superior chemical, mechanical, and thermal stability over hollow fiber UF membranes.
RO modules may be arranged in parallel or series configurations. Each element has a diameter of approximately 12-inches and a length of up to 60-inches. Two to six elements are assembled in a single cylindrical module. The size and the operating pressure vary depending on the installation.
In contrast to UF, a more defined pretreatment is required for reverse osmosis (RO). In general, the water/wastewater should have a low Silt Density Index (SDI) to avoid membrane clogging. RO membranes may also clog via calcium and magnesium precipitation (ions are retained by RO membrane), which can be avoided by water softening. A ultrafiltration stage upstream of RO membranes can remove organics, algae and fine particles to avoid fouling during desalination.
Illustrated below is a conventional RO/NF membrane process diagram.
