Tirupur: The CSIR-Central Salt and Marine Chemicals Research Institute, Gujarat, has come up with a technology to dispose of mixed salt sludge generated in common effluent treatment plants (CETP) in Tirupur textile dyeing cluster.
Since the inception of zero liquid discharge (ZLD) in 2011, more than 30,000 tonnes of mixed salt, a hazardous waste, have been accumulated in the cluster. Now, the developed technology could convert mixed salt sludge into sodium chloride, which could be sold in the market.
The technology was first implemented in Chinnakarai Common Effluent Treatment Plant (CETP) in the city on Friday. State ministers K C Karuppannan (environment), O S Manian (handloom) and Udumalai K Radhakrishnan (animal husbandry) inaugurated the system.
As part of setting dyes in fabrics, lime and soda ash are utilized in dye baths, and resulted in accumulation of lime sludge when dyeing effluents are treated in the treatment plants. The dyeing units have found a solution to dispose of the lime sludge by supplying it as a raw material to cement manufacturing companies.
In the treatment plants, microorganisms including bacteria would be added with the effluents because they would consume effluents. Since bacteria would easily multiply themselves quickly, major part of bacteria would be removed and resulted in accumulation of biosludge. Now, with the help of a research team from Indian Institute of Technology, Madras, the dyeing units got a solution that the biosludge could be utilized as fuel. But the units were waiting for nod of the Central Pollution Control Board for executing it.
With the treatment, the dyeing units can get 90-97% of water and 80% of salt from effluents, and both can be reused. At the end of the treatment process, mixed salt sludge consisted of sodium chloride, sodium sulphate, magnesium and some other chemicals would be generated.
“If 1 MLD effluents would be treated, around 1 tonne of mixed salt sludge would be generated. 18 CETPs and other individual treatment plants, which all serve around 350 dyeing units, would treat at least 10 crore litres of effluents daily. Since 2011, when ZLD was implemented effectively, 30,000 tonnes of mixed salt sludge have been accumulated in the cluster,” said S Nagarajan, president of Dyers association of Tirupur.
To find a solution for disposing the sludge, the association sought the help of CSIR-Central Salt and Marine Chemicals Research Institute in Bhavnagar, Gujarat.
“We have come up with a technological solution, which could convert the sludge into sodium chloride. With a pilot project implemented in Chinnakarai CETP, we confirmed that it is commercially viable, and the salt can be sold in the market,” senior principal scientist Kannan Srinivasan of the institute told TOI.
“Following the success of the pilot study, the full-fledged facility was implemented firstly in the same CETP, which can treat 4MLD effluents. Sodium chloride which is generated out of mixed salt is purer than other sodium chloride available in the market. It can be sold to industries like soap making units, caustic making units, and textile dyeing units, which utilize NaCl as main raw material, functioning in Erode, Karur and Namakkal,” I Sajid Hussain, chief operating officer, Tamil Nadu Water Investment Company said.
“Treating one litre of effluents would cost around 20-25 paise, recycling of water and main salt has halved the cost. Though one kilogram of NaCl could be sold for around Rs 1.5, selling the same would not only help us to dispose it safely but also to further reduce cost of the treatment process,” Nagarajan added.
