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

Advantages and limitations
of the water reclamation
techniques
Besides the above presented technical advantages and limitations of the water
reclamation, water reclamation techniques, economical estimates were given
on the basis of not binding offers from suppliers. Economical estimates are
expressed as US$/m 3 of process water including both operation costs and
investment costs amortized over 5 years. Only the water reclamation equipment
is included, not buffer reservoirs, pipes etc. being equal for all solutions.
Table 3 below gives the comparison in a total overview.
Table 3.
Comparison of 4 water reclamation techniques in reactive dyeing of cotton.
Membrane Chemical
Counte current
Waste-water characteristic filtration precipitation Activated carbon evaporation
Initial high dye concentration 0 0 + 0
High salt concentration – – + –
Detergents and other COD –* – 0 0
High temperature + – 0 +
pH (2)-7-9-(10) (2)-8-10 2-10 (2)-7-10
Costs ≈ 1 US$/m
Signatures: 0 = not influenced significantly, + = positive influence, – = negative influence, * = specific compounds,
e.g. cations, can influence negatively.
3
≈ 1-2 US$/m 3
≈ 10-15 US$/m 3
≈ 10-15 US$/m 3
Surplus costs can be expected for chemical precipitation, as heat exchange and
polishing of suspended solids and excess chemicals may be necessary. The
costs estimates concern the rinsing water except for activated carbon, for
which they concern the dye-bath.
Re-use of water, energy and chemicals
Two water types were reclaimed in pilot-scale: The dye-bath itself by activated
carbon adsorption, and rinsing water by membrane filtration in the nano,
and RO range.
Reclaimed dye-bath Laboratory- and pilot-scale tests with dye-baths reclaimed after decolourization
by activated carbon adsorption showed promising results. A number of
recipes was tested showing that re-use of the warm saline and decoloured dyebaths
was possible with no adverse effects on fabric colour or fastnesses. Not
all types of recipes have, though, been tested, and problematic recipes may
exist. Both the water, the energy content and the very high content of salts are
utilized again by this option.
Reclaimed rinsing water The rinsing water reclaimed by membrane filtration was tested on a number of
recipes and used succesfully for rinsing in all. The hot water re-use speeds the
rinsing process up by a factor of 2 compared to the traditional recipes, thus
saving 50% of the time consumption for rinsing, and thereby increasing production
capacity of the equipment. Both the water and its energy content are
utilized again by this option.
Remanence from
reclamation of rinsing water
Anaerobic digestion of remanences from reclamation of rinsing water was
tested in laboratory scale reactors. A possible re-use of the remanences is to
convert the remanence dye-stuff to biogas through co-digestion in municipal
WWTP digesters together with municipal sewage sludge. The experimental
programme covered four digesters operated in parallel.
85