A capillary 8-inch nanofiltration module purifies water.
Click here to enlarge imageLarge amounts of water are used only once for cleaning purposes in many domestic and industrial applications before they are discharged into the sewage system. Generally, the source for this washing water is potable water or locally pumped groundwater. However, these sources are becoming scarce due to increasing water prices or due to environmental legislation that penalises the intake of groundwater to prevent soil dehydration.
The demand for fresh water is increasing, while the total amount of water on earth remains constant. Surface water pollution and increasing water demands magnify the availability problem. Water purification, therefore, will play a key role in the next few decades as lower-quality sources, such as surface water and treated wastewater effluent, provide the main feed stock for process water production.
Membrane technology is one new treatment method for producing water from contaminated sources. Membrane filtration is a physical separation process that transforms contaminated water into a clean permeate. The properties of the semi-permeable membrane determine the quality of the permeate. A NF membrane removes bacteria and viruses, for example, in addition to pesticides, organic matter, heavy metals, and to some degree, salts. The permeate is high quality and can be used as process water for industry.
The NORIT Direct Capillary NF treats water from various sources in a single step to produce high-quality permeate, which can be used as process water for industry; therefore the NF process is referred to as "direct capillary NF".
The NF process was tested on effluent from a sewage treatment plant and on surface water. Trial studies demonstrated that direct capillary NF with capillaries results in long-term stable flux behaviour with minimal chemical cleanings. AirFlush® stabilised the flux and reduced the amount of chemical cleanings.
Authors' note
Managing Director Bert Welkers, Market Development Manager Harry van Dalfsen and Technology Development Manager Harry Futselaar of NORIT Membrane Technology are based in Hengelo, The Netherlands.