Why is Tirupur called a textile city
Actually, one would hardly suspect it: But it is precisely in "T-Shirt City" in India that the world's most modern wastewater treatment plants are operated on a large scale. In the past, T-Shirt City was notorious for its unimaginable sewage and water pollution. The following report, which we received directly from Tirupur in the south of India, explains how this astonishing development came about - and what problems nonetheless persist. And last but not least, there is still a lot to do for the local textile industry in India (see RUNDBR. 777/4, 696 / 2-4, 520/1, 437/1, 426/3, 390/2, 276/1, 250/1). -hsh-
Tirupur: From T-shirt to inedible groundwater
It is well known that textile dyeing and printing plants are large consumers of water. One kilogram of textile consumes up to 250 liters of fresh water, which is wasted after use. The textile wastewater is highly polluted with dyes, surfactants, dispersants, plasticizers, caustic soda, salts, etc. The news of wastewater-free textile companies is astonishing, especially since it comes from Tirupur in southern India. On the one hand, the city of Tirupur is known as the T-Shirt City. Around 1 million T-shirts, mainly made of cotton, are made there - every day. They are mainly exported to Europe and the USA. On the other hand, this city has achieved inglorious notoriety due to the massive pollution of the Noyyal River there. The original river was a small flowing body of water a few meters wide that often fell dry in summer. For decades, textile dyeing and printing plants have discharged their wastewater into the Noyyal River or into ditches running into it without any treatment. Since a lot of table salt and / or Glauber's salt (sodium sulphate) is used to dye cotton with reactive dyes and the sewage in the river bed seeps into the subsoil, the groundwater became inedible due to the high salt content alone. First of all, a limit value for the salt concentration in the wastewater was set: 2,300 mg / l, but this was not adhered to. -hsh-
Tirupur: Wastewater-free production is forcibly introduced
After much back and forth, in 2011 the environmental authority of the state of Tamil Nadu shut down many of the approximately 700 textile finishing companies. This was the starting signal for unexpected developments. In order to be able to continue producing, the concept of the wastewater-free textile finishing company was compulsorily decreed. Zero Liquid Discharge (ZLD). However, many companies closed at their old locations and moved to the outskirts of Tirupur, up to 50 km from the city. They have invested in new water-saving dyeing machines. The knitted fabric (this is how the "T-shirt fabric" is called) is for the most part refined in so-called discontinuous processes, i.e. pretreated, dyed and finished with chemicals. As with the washing machine at home, the individual treatment baths (liquors) occur one after the other. The modern machines only need 4-6 liters of water per kg of knitted fabric. But since there are many fleets one after the other, it adds up. If, for example, 5 l / kg are used per process step and 10 process steps are carried out, which is quite common, then 50 l / kg are required. Accordingly, 45 l / kg of wastewater are produced; the difference is due to evaporation losses when drying the knitted fabric. -hsh-
Tirupur: How does sewage-free textile dyeing work?
How is that supposed to work so that no wastewater is discharged at all if it still occurs in an amount of 100-1,200 m3 / d per company, depending on the size of the company? Before the technology is explained, it must first be said that some of the textile companies have built their own plants to treat their wastewater (so-called Individual Effluent Treatment Plants - IETP), while others discharge them into collective sewage treatment plants (so-called Common Effluent Treatment Plants - CETP) . The technique for IETP and CETPs is similar. First of all, it is conceptually important that in both cases all the mixed wastewater is treated, although the liquors, as explained above, arise one after the other. You could definitely separate the dye bath and the subsequent wash liquor, as these contain over 90% of the amount of salt - so that a separate treatment is obvious. Some companies have installed the valves and controls for the liquor separation, but then decided to treat the mixture of all the individual liquors, on the one hand to reduce the effort and on the other hand, more importantly, because an important element of cleaning is biological treatment which does not function stably due to excessive salt content. This brings us to wastewater treatment, which is shown in simplified form below. -hsh-
Tirupur: Discoloration with chlorine gas leads to organochlorine substances
First of all, a rake is used to remove coarse materials that should not actually be contained in the wastewater, but which occur here and there due to the carelessness of the employees. This is followed by a fine sieve to separate the larger lint (cotton fibers). The wastewater treated mechanically in this way flows into a mixing and equalizing tank, the volume of which is at least the daily amount, better three times the daily amount. This equalization is good for the subsequent biological level. This is dimensioned so that the easily biodegradable substances are completely broken down by the bacteria. Now it still contains fine bacterial flakes and colloidal substances, but also salt and substances that are difficult to biodegradable or non-biodegradable. The latter include the dyes visible in wastewater. They are decolorized with chlorine gas. This results in organochlorine compounds that are to be assessed very critically, but that no attention is paid to them. The bacterial flakes still contained after the biological treatment are separated out by means of a sand filter, the coarser colloidal substances then in a microfiltration and further, even finer, in an ultrafiltration stage. These are very fine-pored membranes. The wastewater is now practically completely free of solids and colloidal substances. -hsh-
Tirupur: reverse osmosis for the final cleaning of textile waste water
This is followed by three, in some systems four or even five, reverse osmosis membrane stages, in which water is pressed through superfine membranes under high pressure (13-40 bar, sometimes with very high pressure up to 70 bar) so that all dissolved substances, even the very small molecular salt is retained. The completely clean water, also known as permeate, can be used again directly for textile finishing without restriction. The dissolved, non-biodegradable substances as well as the salts are now only to be found in about ten percent of the original amount of wastewater. This so-called concentrate is now a thicker broth that is strongly colored by the dyes it still contains, which, as I said, are among the non-biodegradable substances. It is now further thickened thermally by means of four to five-stage falling film evaporators, but even after that the even thicker and more colored broth is now liquid. The evaporated and then precipitated water (condensate) from the evaporation is mixed with the permeate and can also be recycled. The concentrate is now cooled to 10-12 ° C, sometimes only to 17 ° C, which means that a high percentage of the salt crystallizes out and can be used again in this very fine form for dyeing. But even after this there is still an aqueous residue that is concentrated in a further evaporation plant, partly under vacuum. Then the broth is so thick that it turns into dry salt in a final step. Special dryers are used for this. The residue that ultimately arises contains the non-biodegradable substances and the residual salt that could not be crystallized out. Due to the contamination, it is of such poor quality that it can no longer be used for dyeing and has to be dumped, naturally protected from rainwater. In many cases, the doughy, sometimes completely dry residue is temporarily stored under a roof on the IETP or CETP premises. Now you are at the end, so wastewater-free. -hsh-
Tirupur: Corruption does not spare high-tech cleaning either
The aforementioned procedure is an incredibly complex process, both in terms of machine technology and energy. The operating costs are 3-4 EUR / m3. This hurts the companies, which leads to "cost avoidance measures" in which wastewater, even partially, or concentrates are "disposed of" via dark channels. It is said that the corruption in this "wastewater business" is widespread and that many of those involved are holding their hands, such as representatives of the authorities, plant manufacturers, experts and, not least, politicians. Nevertheless, there are many of these complex systems with which the state of the art has been further developed. In local regions without water scarcity with enough water to dilute salt, so that no groundwater pollution occurs as in Tirupur or aquatic organisms are impaired, the enormous energy expenditure must be compared with the advantages achieved (no wastewater / water recycling, salt recovery). Such a life cycle assessment has not yet been carried out in a clearly comprehensible manner, but it could well be that the high energy consumption is too negative. There is also the cost argument, because the investment and operating costs are considerable. The weighing and evaluation of the advantages and disadvantages should be carried out in a comprehensible manner by means of life cycle considerations. In any case, this Indian development should also be closely followed in the European textile industry. The standards for the treatment and purification of textile waste water are set in the EU by an industry-specific reference paper on the best available technology (BREF). In this respect, the high-tech processes used in Tirupur should be clearly documented in the reference document pending revision on the best available techniques in the textile industry! -hsh-
Bangalore: "When the lake burns" ...
... the weekly newspaper DER FREITAG wrote a report on page 8 on April 6th, 2017 about the appalling reality of wastewater disposal in Bangalore, India. So much untreated sewage is discharged into the largest lake in the 10 million metropolis, and truckloads of rubbish are dumped into it that methane is formed in the digested sludge. The methane has already ignited several times, so that large parts of the lake have gone up in flames. The garbage that burns on the surface of the water has raised the already existing air pollution to an even higher level. Bangalore was previously known as THE Indian "garden city" due to its numerous gardens and the "lake city" because of its almost 300 lakes. Because of the enormous construction activity, there is not much left of the gardens and lakes. The remaining lakes are completely polluted and poisoned. The lakes had previously been created as part of a sophisticated irrigation system in the 17th century. Today, Bangalore in southern India is the center of the military and civil aviation and space industries as well as the Indian IT center. Despite these high-tech industries, there seems to be neither awareness nor money for environmental and water protection.
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