Dyeing textiles without effluent

QUALITY WORKS.

Dyeing textiles without effluent

Clean water is essential for human life. Contaminated water is the primary cause of many infectious diseases, especially in developing countries. In the developing world, and elsewhere, untreated wastewater is still dumped into rivers. This makes it difficult, or even impossible, to obtain unpolluted drinking water. On March 22, 2017, the United Nations World Water Day will remind us of this problem. The aim is to identify and utilize wastewater as a resource.

For example, in the private sector wastewater is produced in sanitary facilities and wherever water is required for production processes. Traditionally, industries such as leather-making and textile production use large quantities of water and generate a lot of effluent. Nowadays, however, liquid waste can be minimized, or even completely eliminated, thanks to highly efficient treatment methods using reverse osmosis and ion exchange. Lewabrane and reverse osmosis elements and Lewatit ion exchange resins from LANXESS play an important role in this.

Modern treatment in India

In Tiruppur, in the province of Tamil Nadu in southern India, at the heart of the Indian cotton treatment industry, there are high-performance treatment plants that serve as a shining example of how modern wastewater management works. In the 1990s hundreds of textile factories, especially the many cotton dyeing factories there, still dumped large amounts of untreated effluent into the Noyyal River, a vital source of drinking water for the entire region.

The effluent situation improved when the Tamil Nadu Pollution Control Board developed special methods of treating the effluent from cotton dyeing factories as part of a country-wide program. Dedicated treatment plants for large textile companies, as well as for small and medium-sized dyeing factories, were and are still being built. Such plants can be ideally combined with existing production facilities. In the case of newly constructed factories, specially optimized production processes offer further opportunities for recycling processed water and avoiding the generation of wastewater.

At present about 24,000 cubic meters of wastewater are treated with membrane elements and ion exchangers from LANXESS in the Tiruppur region. For example, in one textile factory in Tiruppur a total of 154 Lewabrane ROS400 HR membrane elements and 7,500 liters of Lewatit CNP 80 WS cation exchange resin have been used since August 2016 to process about 85 cubic meters of wastewater per hour.

Effluent treatment for dyeing factories – how it works

The multi-stage “end-of-pipe” method – i.e. retrofitted environmental protection measures that do not change the production process but do reduce environmental pollution – starts with biological treatment, separation of sludge and coarse filtration. This removes most of the organic content and dispersed particles, e.g. fibers. After this, the filtrate is bleached and then softened with the aid of ion exchangers. In the next step, a low-salt, colorless permeate, containing less than one percent of the originally dissolved salts and no organic contamination, is produced by reverse osmosis. This can often go right back into the industrial process.

Efficient combination

“The use of ion exchange is a highly efficient method for pre-treating water before reverse osmosis,” explains Alexander Scheffler, Membrane Business Director from the LANXESS Liquid Purification Technologies Division. The salt-enriched low-chloride retentate can either be re-used directly in the dyeing process or further concentrated. Finally the salts, primarily sodium sulfate and sodium chloride, are separated into distinct solids. The sulfate can be re-used in the dyeing process and the chloride can be disposed of. With this process, wastewater is no longer produced. This not only protects the environment, but also has potential to save the textile industry money, mainly thanks to the reclamation of salts. Experts are convinced that all of this could be implemented with almost no effect on production costs if primarily regenerative energy sources were used.

“The example of the plant in India is an impressive demonstration of how very salty water that is also severely contaminated with organic material can be very efficiently purified with a combination of ion exchangers and reverse osmosis,” Scheffler explains.

Two questions: Interview with Jean-Marc Vesselle on the subject of wastewater

Jean-Marc Vesselle, head of the LANXESS Business Unit Liquid Purification Technologies (LPT), answers the following questions on the subject of wastewater at LANXESS: “Which solutions does LANXESS offer for a resource-saving water use?” and “How does LANXESS handle its wastewater an what does the company do in order to avoid it?”.