Evaluation of DOW™ ultrafiltration operation at low temperatures

Ultrafiltration is a pressure-driven technology which provides consistent and reliable filtrate water with low Silt Density Index (SDI), independently of the feed water source. For sea water applications, the feed may vary a lot depending on the location and the season. Ultrafiltration should be able to process very cold water in the Nordic countries which can be below 5°C during the winter to very warm water in the Middle East reaching up to 40°C during the summer. However, it is well- known that temperature has a high impact on pressure-driven UF technology due to water viscosity changes requiring higher pressure to overcome the resistance across the membrane. Apart from viscosity, other challenges that can be thought to affect the ultrafiltration operation at low temperature are the cleaning efficiency with chemicals such as sodium hypochlorite and the possible effect of temperature on porosity of the fiber material. An experiment was performed at the DW&PS Global Water Technology Center in Tarragona (Spain) in order to evaluate if DOWTM Ultrafiltration SFP-2880 modules can sustainably operate with seawater at cold temperatures. The commercial UF modules consisted of modified Hydrophilic-PVDF fibers of 0.03 mm of nominal pore diameter housed in an uPVC casing. The feed water for the experiment was Mediterranean Sea Water from the Tarragona harbor which temperature was adjusted using a cooling system at different set points of 5°C, 12°C and 25°C. From this study was concluded that Dow hydrophilic-PVDF fiber had similar behavior at temperatures between 5°C and 12°C than at 25°C showing stable operation over two months with constant trans-membrane pressure (TMP) and permeability. Although, a higher feed pressure is required when working at lower temperatures due to higher water viscosity, when normalized to 25°C, the TMP and the permeability trends are similar as during operation at higher temperatures.