Cleaner Technology Transfer to the Polish Textile ... - Miljøstyrelsen

3.4 Reclamation and re-use of process
water from reactive dyeing of cotton
Henrik Wenzel, Hans Henrik Knudsen, Institute for Product Development,
Denmark, Gert Holm Kristensen, VKI Institute for the Water Environment,
Denmark and John Hansen, DTI Clothing and Textile.
Abstract
This paper presents Danish experiences with water reclamation and re-use in
reactive dyeing of cotton. Experiences include development of new dyeing
and rinsing recipes and of water reclamation techniques, leading to large savings
in time, water, energy, and chemicals. Investigated water reclamation
techniques are chemical precipitation, membrane filtration, activated carbon
absorption, and counter current evaporation/condensation.
The advantages and limitations of each technique have been identified in labscale
and documented in pilot-scale. An overall solution has been chosen,
based on membrane technology for the rinsing water and activated carbon
adsorption for the dye-bath itself. The solution implies hot water re-use in
rinsing, re-use of filtration remanence in anaerobic digesters, and re-use of
dye-bath water and salts. This solution is implemented as a small demonstration
plant at a Danish cotton dye-house.
Introduction
A large Danish programme for water reclamation and re-use in the textile
industry was initiated in 1992. The programme covers several applications of
water reclamation techniques in textile dyeing and printing with the largest
focus presently on dyeing of cotton. The programme is conducted by a Danish
research group consisting of three institutions: the Institute for Product Development/Technical
University of Denmark, VKI – Institute for the Water Environment,
and DTI Clothing and Textile, and with participation of several textile
companies.
The water generating process studied in this research is reactive dyeing of cotton
knitwear in batch. This process is widely spread world-wide, and becoming
increasingly used. Cotton represents approximately half of all textile
world-wide, and nearly all cotton is today dyed by reactive dyes.
The overall strategy of the research has been to identify environmental
improvements by a stepwise procedure:
1. Process optimisations and water savings.
2. Potential modernisations of dyeing equipment.
3. Chemical savings or substitutions.
4. Water reclamation and re-use of water, energy and chemicals.
This order of priorities should be respected as far as possible in order not to
treat problems that could be avoided succesfully by process alterations.
Not respecting this order of priority could lead to wrong dimensioning of
water reclamation equipment, and in the worst case, total misinvestment.
79