The natural evaporation treatment used in traditional salt plant design used to produce salt from sea water in the eighteenth century Poland and Germany is all set to bail out the crisis ridden Tirupur dyeing sector. This traditional method to separate out salt will be now used to treat the effluent reject water from Common Effluent Treatment Plants (CETP) of the dyeing units.

The natural evaporation method comprises of a wooden structure through which salt water is made to trickle down and evaporate, to separate out the dissolved salt. This was initially called graduation tower in Poland during the eighteenth century and later as Gradierwerk in Germany. The Gradierwerks were converted into spas during the pre and post Nazi period due to the medicinal value of the salt vapour to cure respiratory ailments. The Tirupur based institute NIFT-TEA Knitwear institute has come up with an evaporator based on the German model called Eco Green Industrial Evaporator (EGIE). The Indian Institute of Technology (IIT) Madras has also certified the viability of this method.

"A team of experts from our institute went twice to University of Berlin and had discussions with Florence Schindler, a scientist there who suggested that we use natural evaporator to treat RO reject water from dyeing units to ensure zero liquid discharge," said Raja M Shanmugham, Chairman, NIFT-TEA Knitwear Institute, Tirupur.

The CETPs release two separate streams after Reverse Osmosis (RO) treatment of RO permeate which is close to pure water and RO reject containing toxic waste. The EGIE comprises of a wooden structure with black thorn stems stacked up inside a wooden tower. The RO Reject water will be made to trickle down the structure and it will be evaporated with the help of atmospheric pressure temperature, wind velocity, wind pressure and other atmospheric conditions. "To treat 50,000 litres we have built a model structure which is 21 metres in length, 10 metre in height and 2.5 metre wide. The structure can vary according to the requirement of the individual treatment plants. It also ensures that there is no harmful carbon emission from the plant," Shanmugham added.

Majority of the affected dyeing units have given a thumbs down to the use of mechanical evaporation methods as it cannot ensure zero liquid discharge. The total cost of this structure, with one lakh litre capacity, is around 50 lakh. The basic graduation tower was initially designed by renowned Polish statesman Stanislaw Staszic, one of the pioneers of Polish enlightenment movement.

Apart from this method, some of the CETPS are also trying out Ozone colour removal method for treating the RO reject by converting liquid oxygen in it into ozone (O3) inside a chamber and thereby ensuring zero liquid discharge. Mangalam CETP in Tirupur is trying out this method and is monitoring the end result.

"We are trying out this method and so far the results are better than using mechanical evaporators to treat RO reject stream," said C Palanisamy, General Manager, Managala CETP.