treatment. In Fig 4 the results are shown from spectrophotometric scanning measurements of filtered feed samples and filtered effluent samples from the digesters. From the figure(lelf) it can be seen that in the feed samples no dyestuff was present in the dissolved phase, except for the feed containing membrane remanence, which as expected showed significant amounts of dissolved dyestuff.
From thel figure(right) it can be seen that no dissolved dyestuff was found in the filtered efluent samples, except for the sample from the digester fed with polymer precipitate in which a small concentration of dissolved dyestuff could be observed. The dissolved dyestuff in the membrane remanence thus was degraded through the anaerobic digestion. The small amount of dyestuff observed in the emuent from the digester fed with polymer precipitate indicated release of some precipitated dyestuff caused by degradation of the applied polymer. The released dyestuff concentration is small and will be invisible when possibly returned into the sewage with the reject after sludge dewatering.
5.Environmental benents
For reclamation and reuse of the rinsing water a comparative study of the environmental impacts Aefare and after rinse water reuse has been carried out(Fig. 5) The study concerns a reuse solution based on membrane filtration. All chang included in the study, including also the membrane plant, reservoirs, etc., from raw material extraction to production, use, and disposal of the equipment[1]. This study is a socalled lifecycle assessment of the solution, performed according to international practice l12,13]. The study concerns only environmental impact from the rinse process.
6. Conclusions
The optimal solution has been found to be to separate the process water into two water types: (1) dye bath the first rinse, and(2) rinse water. Dye bath can be reclaimed by adsorption of dyestuff and COD on activated carbon, and reuse of the reclaimed dyebath, including salt content, seems possible from pilotscale studies. The economic value of the salt content of the dye bath is equal to the cost for reclamation, rendering the solution economically feasible.
Recipes for rinsing can be altered to leave out dispersing and complexing agents completely. provided that pretreatment is well performed and provided that soft water is used for the rinse. The rinse water can be reclaimed by membrane filtration in the nanofiltration and RO range and reused for rinsing purposes. Operation at 90°C and been shown feasible giving very high fluxes allowing for direct hot water reclamation and reuse without supplementary heat exchange. Hot water reuse speeds up the rinsing process by a factor of 2 com pared to the conventional recipe, increasing production capacity of the equipment substantially. A lifecycle assessment has shown that environmental improvements by such a new recipe based on hot water reclamation and reuse by membrane filtration are great
Dyestuffs in remanences from membrane filtration are degraded in anaerobic digestion with no negative influence on performance of the digester.
A demonstration plant based on these solutions is under construction at a Danish cotton dye house.
Acknowledgement
The project for water reclamation and reuse in cotton dyeing is sponsored by the Danish Council
for Recycling and cleaner Technology. We would especially like to acknowledge the programme chairperson, Ulla Ringbaek, for making the project possible and for her constructive com ments and kind help