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Membranfiltrering af afsletningsvand i textilindustrien

Summary

The basis for the project was the fact that desizing of woven textiles generates wastewater with a high content of COD. It must, however, be expected that the partially decomposed sizing chemicals relatively easily can be removed through an appropriate filtration process, and afterwards the water, containing energy and possible auxiliary chemicals, can be reused.

Therefore, the purpose of the project was to find the most suitable process of filtration of desizing wastewater through testing in laboratory and pilot scale as well as testing in full-scale. The economical and environmental consequences with this process should be covered at the same time. The pilot scale and full-scale tests have been implemented at Nordisk Blege- og Farveri in Helsingør. The desizing is carried out partly by oxidation and partly enzymatic.

Quickly, we could state that purification and recycling of wastewater from synthetic sizing chemicals already have been subject to extensive investigations. Therefore, it was decided that the project should concentrate on natural sizing chemicals – usually natural starch or modified starches, which at the same time exist most frequently at the company.

A number of membrane types were tested in the laboratory with the actual wastewater, and the tests resulted in the first selections of membranes to the pilot scale tests.

Two series of the pilot scale tests were carried out. In the first series, focus was primarily on the oxidation process. However, it turned out to give some practical problems, especially in connection with the risk of re-precipitation of size in the membranes. Therefore, the other series only tested the enzymatic decomposed size, and here it turned out that both nano and reverse osmosis membranes can be used for the purpose.

A full-scale plant was afterwards designed and delivered to the company. It was designed to treat the wastewater from enzymatic desizing from the company's 9 jiggers. Nano-filtration was selected with a capacity of 21 m³ during 24 hours.

The plant has been running for a period with current adjustments, and some plant components have been changed. Experience from 6 to 7 months running time exist, but this period is too short to give reliable knowledge about the lifetime of membrane elements and optimum cleaning procedures. The purified water has been reused without any problems.

However, we have outlined a financial potential, which shows that the plant in question will have a simple payback time of between two and three years, if it is fully run. We have not included any expenses for possible changes of membranes, purification chemicals, electricity and removal of concentrate.

The removal of concentrate has not been finally clarified. Tests show that concentrate will be suitable for biogas production and as carbon source in connection with denitrification. Negotiations are conducted with Helsingør Municipality about delivery of the concentrate to one of the treatment plants, which carries out denitrification.

Therefore, we can conclude that membrane filtration can be used for separation of wastewater from desizing in clean water for reuse and concentrate, which can be utilised. The financial circumstances have not yet been finally clarified.