Omsite colour removal at Courtaulds Textiles

Rebecca Reid reports on a technological breakthrough in effluent treatment and water

reuse at Courtaulds Socks

Courtaulds Textiles started to focus on the problem of the environment in the late 1980s when it formulated an environmental policy and started to implement various action plans. The environmental impact of its processes, compliance with regulations, supplier relationships, process development, budget formulations for controlled equip- ment and cost recovery were all important aspects, and the overall plan set tough but achievable targets for effluent discharge compliance, energy use reduction, waste reduction and recycling. The high environmental impact of the dyeing, printing and finishing businesses made them a particular priority for consideration [1,2]. One of the group’s recent successes has been an on-site colour removal system which has been fully operational at its Courtaulds Socks subsidiary in Leicester since November 1995.

As chief executive Hamid Khan explains: ‘Courtaulds Socks is the largest British sock manufacturer and a dedi- cated lead supplier of men’s, women’s and children‘s socks to Marks & Spencer. There are over 450 employees at the Leicester site and we are investing heavily in the environment as well as in plant, equipment and people.’ The pro- duction includes cotton/nylon, wool/nylon and Lycra blends, all of which are dyed on site. Effluent is discharged to sewer- age and processed at Severn Trent’s Wanlip treatment works. As the residual colour in dyebath effluent, particularly from reactive and acid dyes, is not removed by conventional biological treatment systems, the cost of the ter-

Figure 1 Duty and stand-by pumps for the automated dosing of various chemicals: the white tank is the separator, the black ones are chemical holding tanks

Figure 2 Reagent assembly:

the first reaction tank (far right) and sludge sump (large flat tank)

can be seen in the background

tiary treatments required at Wanlip is being passed back to textile processors in the Leicester area. It was the potential - and significant - effect on profitability of these extra charges, which are also in operation at Leek in Staffordshire, that prompted Courtaulds to investigate methods for removing the residual colour on site. (For industry-wide reviews of the problem of colour in dyehouse effluent see [3].)

The system which Courtaulds Textiles chose (and developed in partnership with Crosfield Chemicals and the engin- eers from Bergmann Technology, a

division of Linatex) relies on the use of Crosfield’s Macrosorb absorbents: synthetic organic clays that can bind the dye molecules and hold them in inert, pumpable sludge. This is the first UK application to combine absorption and coagulation technology in this way. The success of initial bulk trials (with 10% of plant flow) encouraged them to build a half-size pilot plant, and the present full- size plant (Figures 1 and 2) has been operational since July 1995, and for the last 4 months has been working 24 hours a day, 7 days a week to keep Courtaulds Socks’ discharges within the limits

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agreed with the water company. Figure 3 shows how, after initial

balancing (to smooth out any peaks and troughs in the dye and chemical con- tent), the effluent is treated with Macro- sorb slurry in the reaction tank. Agitation ensures adequate contact and absorp- tion, and this is followed by an alkali shock where metallic acid salts are converted to hydroxides, producing a primary floc from the dissolved organic contaminants. The colour is completely removed, levels of chemical contamin- ants are significantly reduced and the suspension is weighted, aiding later settlement. The mixture is agitated again and flows towards tank 3, where it mixes with a high molecular weight coagulant. A proportion of the sludge separates out at this stage and the remainder is removed as the mixture passes through the array of closely spaced inclined plates in the Crossflow clarifier.

The sludge can be concentrated, ultimately to filter cake, and Courtaulds Textiles has experimented with using the dried sludge as a growth support medium (last year they grew lettuces). However, at the moment the best option seems to be discharge into the sewer and, as the material is inert, Severn Trent has agreed to accept it as a suspended solid.

The effluent, which meets the colour standards, is now suitable for discharge to waste - but there are other, and even more technically-effective uses for it. As Peter Cooper, Courtaulds Textiles group technical director, explains: ‘Early on in the testing process we became aware that there was a substantial possibility of reusing the treated water in the dyeing process.’ This was indeed the case, and Courtaulds Socks is now able to reuse 50% of this treated water in the wet pro- cess - with no effect on its right-first-time dyeing performance. The advantages in- clude a reduction in the overall water intake and effluent volume, and the fact that the water has already been heated and softened. Other pluses are that the plant needs very little attention, although skilled technical management is a pre- requisite to ensure the use of treated water is adequately controlled. From an engineering point of view, the plant is small (250 m2 in area), very highly auto- mated (which has both cost and health and safety advantages) and easily expandable.

Peter Cooper and Grahame Birch, the

Clarlfied water

Sludge to treatment or disposal

1 Acid 2 Macrosorb 3 Dilution unit 4 Tank1 5 Tank2 6 Alkali 7 Effluent 8 Coagulant 9 Clean water

10 Metering pump 11 Flocculated feed

to clarifier 12 Tank3 13 Air compressor 14 Tank4 15 Sludge discharge

valve 16 Control unit 17 Sludge hopper

Figure 3 The treatment system. Macrosorb and acid are added to effluent in tank 1 (the reaction tank), with agitation to ensure contact. The alkali shock between tanks 1 and 2 produces primary floc from dissolved organic contaminants. High molecular weight coagulant is added and a proportion of the floc sinks to the bottom of tank 3. The remainder is separated in tank 4, the Crossflow clarifier. The sludge can be compacted or discharged as slurry, while the effluent (clarified water) can be discharged or re-used

technical manager at Courtaulds Socks, are very proud of the plant’s per- formance, as are Keith Cockett, project director at Crosfields, and Jon Woolins, product manager at Bergmann. Cour- taulds Textiles is so pleased with pro- gress that it‘s using the equipment as the basis of a full effluent treatment plant at its joint venture site in Nanjing, China. There, the UK-proven chemical plant is being combined with microbiological polishing to ensure that water course discharge complies with the equally stringent standards the Chinese govern- ment has specified for such projects. Courtaulds Textiles is also considering using the technology at other locations,

for example in the Philippines and elsewhere in the UK and Western Europe - which just goes to show that effluent isn’t always a problem and its treatment and reuse can be a viable business process.

References 1. 2. 3.

P Cooper, J.S.D.C., 109 (1 993) 97. P Cooper, Knitting Int., 102 (1 995) 62. P Cooper (ed). Colour in Dyehouse Effiuent. 1995, Society of Dyers and Colourists, Bradford, UK.

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