Water and wastewater filtration: Process design: Fid-Bau Portal

Water and wastewater filtration: Process design

Pearce, Graham

In the fourth in a series of articles describing membrane filtration technology used for water and wastewater treatment, this review discusses process design issues, and looks at the reasons for the different approaches taken by suppliers. Reverse osmosis (RO) and nanofiltration (NF) have evolved common process designs and interchangeable products. In contrast, membrane filtration products in both ultrafiltration (UF) and microfiltration (MF) show considerable diversity of approach between manufacturers. This is partly due to the fact that RO has been commercially exploited for much longer, but also due to the nature of the technical duties in UF/MF, which makes several closely competitive approaches possible. The main commercial UF/MF products are all based on capillary membranes. Also, they mainly use a dead end or direct flow process design concept with an intermittent cleaning cycle. However, within this broadly common approach, several different process design options have developed, which has deprived end users of interchangeability of products within their processes as has been widely adopted in the RO/NF field. Some products use a feed on the inside of the capillary lumen whilst others feed on the outside. Another distinction is whether the process design is pressure driven, with a pumped feed, or whether the membranes are submerged in the feed tank, with die driving force applied by suction on the permeate side. The different approaches taken by manufacturers are largely dictated by the membrane polymer selected. This article will review the choice between inside and outside feed configurations, and the merits of pressure driven vs. submerged approaches. Finally, the issue of module orientation will be examined.