The textile industry needs a lot of water, in both pre-dying procedures and subsequent finishing treatments : overall, 100-150m3 are needed for each tonne of cloth treated.
The great variety of textile fibres and colours available today means that water is used as a method of treatment or as an addition to a large number of chemical substances. More than 4,000 different compounds are employed nowadays, and generally they wash up in the waste water at the end of the industrial process.
At present all textile factories have a waste treatment plant, either shared with others in the same area, or at the level of the individual company. However, there are some chemicals that are difficult to eliminate completely. For these, additional treatments are increasingly expensive.
In order to reduce costs and increase supply chain security, even during droughts, the textile industry is trying to develop procedures to reuse waste water. These procedures must be effective, but above all economic, given that the sector is very competitive.
One fundamental contribution to these studies has come from the Prato (Tuscany) textile industry. Here, an industrial aqueduct, in existence for many years, distributes recycled water which has been cleaned using methods which are simple yet reasonably efficient (settling, decanting, sand-filtering). The same type of industrial aqueduct is in use in the Como area. Experience in the use of these industrial aqueducts has shown that the main factor limiting water re-useis the presence of residues from dyeing. Even in small quantities, these can result in undesirable colours in the water and hence in the fibres with which it enters into contact. This limits the use of cleaned water to the initial phases of the process, mainly to remove dirt and foreign bodies still stuck to the fibres.
Amongst the current proposals for getting round this obstacle, biosorption using fungus (Cunnigamella elegans) must be mentioned. Tests undertaken by Turin University show that dyes used for wool, cotton and synthetic fibres can be neutralised effectively, even when the baths have been used many times and where there is a low concentration of dye.
This process has proved to be much quicker; in fact, the elimination of the colour happens mainly in the first two hours of treatment – biodegradation with selected micro-organisms (Bjerkandera adusta in particular). According to the Turin University study, looking at dye residue from dying wool in acid baths, more than 90% of the colour can be removed in 24 hours.
Another possibility is treatment by chemical oxidation using ozone, combined with tangential filtering on flat membranes. Testing this combination was the purpose of the Prowater project, which won the “Best Life Environment Project 2007-2008” in the water management section. It was carried out by the Next Technology Tecnotessile company.
The European research project ADOPBIO (Advanced Oxydation Processes and Biotreatments for Water Recycling in the Textile Industry) has studied a combination of several advanced oxidation processes (with UV light and oxygenated water) and bioflotation. The results seem particularly promising, in terms of both technology and cost.
(Hi-Tech Ambiente, Italy, www.pubblindustria.com)