Dyeing units of Tirupur: Solution for Sludge?

History

Way back in the 70s, Tirupur manufactured white bleached garments for the domestic market. A shift in the market segment came up in the early 80s when export orders overshot domestic demand. Initially, a few units dipped garments in crude single colour solutions but with increasing demand, the number of units grew leading to increased effluent discharge. The six to eight tankers of water consumed, flowed out of each unit in various colours into the river. Resultantly, the tanks and the dam connected to the river too got polluted, affecting the nearby villages, farms and cattle.

Thus, the Tamil Nadu Pollution Control Board (TPCB) intervened, slowly pressurising the dyeing units to adhere to the rules of wastewater management.

Implementation

“The TPCB first asked us to ensure that the water released from the factory was colourless,” said A. Selvaraj, Managing Director, R.A. Textiles Process (P) Ltd. “Then began the process of effluent treatment focusing on releasing colourless water. Soon, we were asked to meet the pH levels and we installed systems to reduce Total Dissolved Solids (TDS) levels in the effluent. Finally, PCB asked all units to turn to zero-discharge plants.”

Today, 80-85% of the dyeing units in Tirupur have effluent treatment plants in place and have achieved zero-discharge. Some of them have installed a full capacity ETP within their premises while some bigger units jointly have installed CETP.

“The effluent treatment involves RO treatment, Nano filter treatment and multiple & solar evaporation, which we have installed at our plant,” said Selvaraj. The disposal of sludge generated after waste treatment is a big problem in Tirupur today. The cost of shifting sludge is a whooping र 6000 per ton! “Therefore, it is not economically feasible to shift the sludge from the unit to the specially created Gummidipondi dumping yard near Chennai. We have built a deep sludge tank surrounded by three feet wide wall. The bed of the tank is laid out with two-sheet protection which does not allow the sludge water to seep into the ground. A small outlet from below the tank is connected to a water tank where water drained from the sludge is collected and treated for reuse in the manufacturing process. But we are awaiting approval from the TPCB to use this tank.

“We have also installed three borewells to check the ground water pH levels. Even though we have got solutions to treating all the waste generated, we are left with an uphill task of storing sludge. Some of the units are doing the trial run of a new method which involves treating sludge with chlorine, but it is yet to attain TPCB approvals. In the next eight years there would be no space to store sludge.”

Lack of guidance

If R.A. Exports has been able to tide over the sudden ‘diktats’ of the PCB, many other factories are in dire straits. There are units that have failed to install proper ETPs owing to huge investment costs or lack of space. Some smaller units have shut operations too. Few of the bigger units have jointly invested, by obtaining loans, in common effluent treatment plants to meet TPCB requirements. The Association of the garment manufacturers has played a vital role in holding the industry from crumbling. There is a general feeling among the industry players that if they had been guided into installing ETP right at the time of beginning operations, they wouldn’t have had to see this day.

The process

Twisted rolls of white bleached fabric curl out from state-of-the-art machines and get collected in Sintex industrial containers before it is taken up for dyeing. The dyeing process begins in the lab at R.A. Exports, where samples are tested to match colour. A final recipe of the exact shade, as per the client’s specification, is passed on to the factory. R.A. Exports manufactures yarn, knits and dyes fabric. Bold shades of reds and greens bathe the white fabric in large machines that rotate at high speed. The entire process being automated, there is no spillage of either dye or water.

“If you see the floor at the workshop, it is hardly wet. Only when we unload the boiler, there is water spillage, otherwise all the outlets are connected internally. The floor is washed with water by the workers themselves during the change of shift in the evening,” said Selvaraj.

Effluent treatment

The remnants released from this water- and energy-intensive dyeing unit are carried by effluent trenches to the ETP. These trenches carry wastewater to the Aeration Tank (designed by Hydroair, Navi Mumbai), where the effluent passes through various stages before it is aerated to meet the Chemical-Oxygen Demand and the Biological Oxygen Demand levels.

From the reaction tank to collection tank to the primary and secondary clarifiers, tertiary treatment and finally to the aeration tank, effluent is constantly treated and water recycled through an RO (5ppm) to be reused in the manufacturing process.

At the equalisation tank, the pH of various chemicals is neutralised. “Chemicals, both acidic and alkaline, are used in the manufacturing process. The pH levels are brought to 7-8 through equalisation. The wastewater is then treated with ferrous chloride and lime powder which coagulate the effluent to separate the dye water and sludge. While the separated sludge is treated at the sludge drying bed, the water collects at the primary clarifier where it is further coagulated. The excess water is directed to the aeration tank. It takes around 10 hours at the aeration tank.

Tertiary treatment uses sand filters or carbon filters to remove suspended solids, colour, organic impurities, etc. The aeration tank treats the chemicals present in the water biologically with bacteria, which eat up the chemical to meet the COD and BOD levels. For the bacteria to survive, this machine runs 24/7.

Finally, at the RO plant, water is processed clean with nano filters. Directed and commissioned by Alpha Water Technologies, the RO system is maintained by engineers in the unit who received six months training from Alpha at the time of installation. “Initially, the RO was used to clear the water only, but when it came to zero-discharge, we installed nano systems. In this process, the brain and the nano reject are separated. The rejects from the brain or the sodium chloride solution contains TDS which again is sent to the multiple level evaporator. Around 3000-4000 litres of leftover water from the multiple evaporator is directed to the solar evaporator.

“The final sludge generated after effluent treatment is highly toxic and cannot be reused. Since we are only operating at half our capacity, we have been able to dump sludge in the backyard. As a short term solution, we have built a huge tank and laid it with geo-permissible sheets to store sludge cakes. But after eight years, storage of sludge will pose a problem and the only solution left with us would be to move out,” said Selvaraj.

R.A. Exports has also taken efforts to green the premises, which is filled with coconut trees. “Boiler ash acts as good manure and we are in the process of making more plantations.”

CETP

Around 24 dyeing companies have joined hands to set up a common effluent treatment plant in Sirupulopatti, Tirupur. Being erected by Hydroair, the RO and NBR technology has been from ITT, a UK based company, said N.V. Murthy, Partner, Alagenra Exports.

The total project cost of र 50 crores has been partially funded by UCO Bank (र 35 crores). “The initial 20% was contributed by the manufacturers jointly and a trial run of 200,000 litres of waste treatment was carried out for four months. The plant, which is likely to commence operations any time now, will be maintained by Hydroair for the first year,” said Murthy.