Coimbatore residents oppose setting up of sewage treatment plant

Threaten to sit on protest if the plant is not relocated

By Soundaram Ramanathan
Published: Friday 28 December 2012


Angry with the Tamil Nadu Pollution Control Board (TNPCB) for giving its consent to start operations of a sewage treatment plant (STP) near Nanjundapuram in Coimbatore, residents have threatened to begin protests if their demand to relocate the plant is not met.

It is essential to obtain the pollution control board’s consent to begin operations of any sewage treatment plant. The Coimbatore corporation was given Rs 373 crore under the Jawaharlal Nehru National Urban Renewal Mission to set up plants at Ukkadam, Nanjundapuram and Ondipudur and a 650-kilometre underground sewerage line. The plant at Ukkadam, of 70 million litre per day (mld) capacity, has been operating since last year. The plant at Ondipudur is under construction. However, the two plants were not opposed because they are not in urban areas.

Hindustan Dorr Oliver Ltd, which has been given the contract to construct the 40-mld plant at Najundapuram, will use the cyclic activated sludge technology (see ‘How the plant works’). Here, the technology will be fully automated through supervisory control and data acquisition (SCADA) software system. This means, there will be minimum human interference in the treatment process.

How the technology works
  1. Wastewater is passed through big sieves which remove large particles like plastic bags. This water is then passed through multiple-sized sieves to remove smaller solid particles. Water is then collected in a collection well.
  2. Froth floatation process removes suspended solid waste particles. Then, wastewater is directed into grit chambers which remove sand particles in water. A machine separates sand and other grit particles.
  3. Water is then sent to a batch reactor. Here, a calculated amount of oxygen is passed through tubes to aerate the sewage for two to three hours. During aeration, carbon in wastewater gets converted into carbon dioxide.
  4. Now, the sludge in the water is allowed to settle. Bacteria in the wastewater eat nitrates in the water and nitrification process takes place. Thus, nutrients in the water are removed. The settled sludge is removed and centifuged. Centifugation is the process of removing water from the sludge and making a sludge thick solid mass which can be used as fertiliser.
  5. Treated water is finally sent for chlorination. The water which comes out of the chlorination chamber is released to natural waterbodies.

Though experts say it is the best technology to adopt, the plant’s operations will require technically skilled people. D D Basu, advisor, Centre for Science and Environment says the technology will not emit too much odour. But if the plant gets choked, it will be difficult to restart operations. Also, its maintenance is very essential, he says.

Long-drawn demand

Residents have been demanding relocation of plant ever since constructions began in 2009. Residents Welfare Association, Najundapuram filed a case against it in Madras High Court in March 2009. The case was dismissed in April the same year when the corporation admitted not having taken the required permissions to start the plant. The corporation agreed to halt construction till it got clearance from TNPCB.

In its order, the high court had asked TNPCB to take people’s viewpoint before setting up the plant. Thereafter, several meetings were held between TNPCB officials, petitioners and the corporation officials. TNPCB asked the corporation to change the design of the plant. In November this year, the board approved the new design, which the corporation submitted. People, however, say not much change was made in the design.

“The plant is being built very close to our residences. It threatens our health,” says R I Seshan, retired air commodore and a resident. There should be 250 metre land vacant between the plant and the nearest habitation. This has not been taken care of, he alleges. There are four huge chlorine tanks in the plant. If these leak, it can be hazardous to people’s health. A 2,000-hp blower has been installed, but no step has been taken to mitigate the noise from it, he says. “Precautions must be taken to offset any damage if there is failure of any kind. There could be power failure, the generator may fail, the aerobic process may become anaerobic, the plant may start emanating harmful gases like carbon dioxide and methane,” he says. Earlier, TNPCB had seriously objected to the plan of releasing treated water into Noyyal river. So the corporation decided to sell the water. But the plant does not have storage facility. What if the corporation is unable to sell it even for a day? he wonders.

Deputy mayor S Leelavathiunni says the plant is for people’s good. K Ravichandran, district environmental engineer at TNPCB is also confident about the plant. The board gave its consent because there is no fault in the technology. “People should understand that the process will take four hours in a day. So, the odour is not going to be as big a nuisance as is being perceived,” he says.

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