Technologies: Nanofiltration (NF)

Water Recycling in the Paper Industry

Without a system for recycling water, freshwater consumption in the paper industry would be more than 100 litres per kg of paper. The introduction of internal recycling systems and, where possible, the use of biologically treated wastewater can reduce the use of freshwater down to approximately 12 l/kg of product.

The wastewater loading from used paper handling plants is particularly high. New production plants show that, with help from membrane technology, it is clearly possible to:

• reduce the specific water consumption;
• produce high quality process water;
• increase the running times of paper machinery.

Economic production of paper can be improved through the installation of membrane technology.

Example: Palm-Eltmann Paper Factory

Nanofiltration plant at the Palm-Eltmann Paper Factory

When the Palm Paper Factory increased their production capacity of newspaper by 420,000 t/year the existing biological treatment plant was also extended. A sand filtration bed was installed to remove any biological solids that were carried over from the biological unit. Following this step the water was recovered as process water by means of a nanofiltration plant.

This process combination ensures that any COD, colour or AOX that remain in the water following biological treatment are completely removed. It is therefore possible to reuse this water in the production process at extremely sensitive points in the paper making process, whilst at the same time ensuring that all consents are met for the direct disposal of wastewater into the Main River.

Softening Drinking Water

An overwhelming proportion of freshwater consumed in UK households is not used as drinking water, but is instead used in various household tasks. In these circumstances, a high water hardness proves to be a major disadvantage for the consumer. Calcium deposits on household appliances and sanitary fittings are particularly unwelcome. In addition, a high water hardness leads to a higher consumption of washing and cleaning chemicals, as well as salts used in the operation of ion exchangers, for example in washing machines.

Cost of hardness reduction using nanofiltration

For the average household (240 m³/year consumption)), it has been estimated that a reduction in hardness (ca. 1.25 m mol/l) can lead to a minimum cost saving of EUR 78 per annum.

The consequential increase in the cost of treating drinking water is negligible. The application of nanofiltration in the softening of freshwater has already been undertaken by Wehrle in Germany. The capacity of the plants already installed is almost 1.5 M m³/year. Over the next few years plants with capacities of up to 50 M m³/year will be built.

The advantages of Wehrle’s nanofiltration systems include:

• Selective separation of hardness constituents
• Separation of bacteria and viruses
• Reduced energy consumption
• Reduced expenses in consequent treatment
• An overview of the advantages of WEHRLE water softening:
• Reduced investment and operating costs
• Unloaded retentate (Direct disposal possible)
• Environmentally friendly solution
• Reduced problems in corrosion
• Many years of experience with membrane technology and nanofiltration