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Cleaner Technology Projects in Denmark 1997
Kemikalie-, energi- og vandforbrug i tekstilindustrien
Arbejdsrapport nr. 95, 1997, Miljøstyrelsen
The aim of the project is to clarify the potential for membrane
filtration as a separation technique in connection with the recycling of the chemical
contents, energy contents and water in different types of process water from textile
printing houses and textile colours.
Results that are referred to in collected literature and laboratory and pilot test
carried out in this project show that the environmental as well as the economic potentials
for membrane filtration in the recycling of chemicals, energy and water in the textile industry’s different process water types is
large.
Seven chosen process water types from seven industry-typical processes have been
treated with a membrane palette of 31 different membranes in total. The majority of the
membranes in the pilot tests have been sorted in spiral-designed elements.
The process water from the pre-treatment of cotton can, aided by
ultra-filtration, be separated in a permeate containing recyclable detergent, sodium
hydroxide and energy and in addition in a concentrate with a very high COD
that potentially can be used as an energy source.
The dye bath from the reactive colouring of cotton can, aided by specially chosen nanofiltration membranes, be separated in a permeate
containing sodium chloride that can be re-cycled in the colouring, and in addition in a
concentrate with a very high COD- and colour contents, which must be disposed of by for
example using its energy contents. It has only been possible to carry out these tests in
the laboratory.
Both rinse/wash water from the leaching after a reactive pressure of cotton, and from process water from the colouring of polyester
and polyamide, can aided by nanofiltration membranes be separated
in a recyclable permeate with energy contents and a concentrate with a high COD- and
colour contents, which must be disposed of by for example using its energy contents.
Process water from the stonewash of denim goods can, aided by a two-step treatment with
firstly nanofiltration membranes and secondly reversed osmosis membranes, be separated in
a recyclable permeate with energy contents and a concentrate with a very high COD- and
colour contents, which must be disposed of by for example using its energy contents.
Process water from pigment printing of cotton goods can, aided by tubular
ultrafiltration membranes, be separated from the latex contents that make the water type
very difficult to handle in traditional membrane filtration plants. In the concentrate
from the ultrafiltration latex precipitates in lumps that resemble chewing gum. The
permeate is regarded as upgradeable to recyclable water by reversed osmosis. This reversed
osmosis step has not been tested.
The process water types are very different in composition and the results from the
tests also show very different membrane results, and it can be concluded that it is
relatively easier to treat single water types than mixed wastewater consisting of a large
number of different water types.
The tests show very different fouling speeds. Some water types
only need rinsing with warm water to obtain a total restitution of the membrane, while
others need frequent and thorough cleaning procedures to maintain the product flux.
In all of the treated process water types there was, aided by chemical datasheets,
identified chemicals, which potentially could cause problems for the membranes. A
consequent laboratory screening of the membranes acquitted roughly half, the rest are
attempted replaced.
To be able to assess the economic potential of the concept, the actual price level of
the traditional product with the purchasing of water and the payments to the waste water
discharge in Ringkøbing County (22 DKK/m³) can be compared to the calculated price level
of the concept with membrane filtration, recycling of chemicals, energy, water and
anaerobe out rotting of concentrates, which amounts to approx. 17 DKK/m³. This result
shows therefore that compared to traditional production there for the majority of water
types will not be increased costs connected to the implementation of the membrane
filtration concept, and that there most probably could be an economical gain.
Author/ institution
Hans Henrik Knudsen and Henrik Wenzel Christensen, Institute of Product Development
Jørgen Wagner, Osmonics Desal, Bodil Mose Pedersen and Per Elberg Jørgensen, VKI
Institute of Water Environment, John Hansen, DTI Clothing and Textiles.
This report is subsidised by the National Council for Recycling and Cleaner Technology
ISSN no. 0908-9195
ISBN no. 87-7810-913-2
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