Toxic threat to Chennai’s groundwater

CHENNAI: While on the one hand, government and enterprises are working together to reduce pollution -- be it through plastic ban or PCB crackdown against polluting units in North Chennai -- on the other, cost concerns seem to outweigh environmental safety norms.  A cluster of tanneries based in Pallavaram are working to lay a 13.5 km-long underground pipeline to transport treated effluents to the Perungudi Sewage Treatment Plant.

Why? Because the Zero Liquid Discharge system -- that they are required to use -- “costs a lot to maintain” and encounters “technical glitches”. The pipeline project, pegged to cost about `40 crore -- has received a No Objection Certificate from the TNPCB. Construction is likely to begin in April. While industrialists have welcomed the move, ecologists are worried about the potential damage it can cause to water bodies and groundwater.             

Currently, there are 130 tanneries in the Pallavaram cluster that generate close to 2 million litres per day (MLD)of effluents, which is treated at the Common Effluent Treatment Plant that has a capacity of 3 MLD. But that is not enough. To adhere to the pollution control board norms, tanneries must maintain a low rate of Total Dissolved Solids (TLD). They are supposed to send the treated effluents to a Zero Liquid Discharge (ZLD) system to completely eliminate any discharge. 

But the Pallavaram Tanners Company has not been doing that. The (ZLD) system installed at their premises 10 years ago is not being used anymore. They are currently dumping the treated effluents into Adayar River. But since this does not solve the problem of maintinating a “low TLD rate”, they have come up with the pipeline idea. Their effluents will now be taken to Perungudi sewage treatment plant, mixed with domestic sewage and then released into Buckingham Canal. 

What’s wrong with ZLD?

A highly placed source privy to the matter explained the issue the tanners have with ZLD. Due to high contaminants in the reject water, the zero liquid discharge system is unable to turn the effluents completely into salt crystals. Instead, it turns into a paste-like consistency. “This is because of improper biological process. Reject water will have five times more toxins than the effluents. If the effluents are treated more rigourously, salt formation will not be a problem,” says the source.    

The tanners have a different theory: “To be environmentally friendly, we did try to use the ZLD system. As we convert only semi-finished goods unlike other tanneries in the State, our effluents have low levels of dissolved solids -- at 6,000 mg/l. Because of this, the salt in the effluents does not crystallise and instead turns into a paste,” says Mohamed Nazeeb, MD of the Pallavaram Tanners Industrial Effluent Treatment Company (PTIET).

What’s wrong with the pipeline?

Remember the 2012 Tondiarpet oil leak? A major leak was detected then in one of Bharat Petroleum’s pipeline transporting crude oil from Chennai Port to refineries. The accident severely contaminated groundwater table. Experts fear a similar scenario could occur here — industrial waste, though treated, contains contaminants that can pollute groundwater and damage human health. 

“This development will definitely have a disastrous consequence on Perungudi wetlands. The high salt content in the effluents will corrode the pipeline much faster. Also, Buckingham Canal acts as a natural barrier to prevent seawater intrusion. If salt content increases, the canal’s effectiveness to act as a barrier will decrease,” says S Mohan, Professor of Environmental and Water Resources at IIT Madras. The company members defend this theory. They say `15-18 crore was spent just on the pipeline, to ensure they are leak proof. 

Why did PCB allow it?

A TNPCB official confirmed that it was the board’s decision to allow the company to take up this method. “We found several glitches in their Pallavaram ZLD plant. Also, unlike in Ranipet, Ambur and Vaniyambadi, enough sewage is generated in Chennai city to mix it with the effluents in 4:1 ratio. This will lower the TDS rate. The same method is already in place in Madhavaram where effluents from CETP is mixed with sewage from Kodungaiyur treatment plant.” 

Poor record in city
Interestingly, of the 14 CETP facilities across the State, only the ones in Chennai do not follow the Zero Liquid Discharge model. In the ZLD model, toxic effluent is converted into salts. This will prevent it from being released into water bodies or farmlands and thereby harming human or animal health. In this process, 80 per cent of tannery waste is treated through reverse os mosis method while 20 per cent is evaporated to obtain salts.

Success story
“In Ranipet, we too convert semi-finished goods. But our inflow TDS alone is 14,000 mg/L. After reverse osmosis, it increases to 65,000. In Pallavaram, they use more water, hence dilution is high. But even then it’s not possible to have such a low value. Though we spend `1.10 crore a month on ZLD, it is the safest method of disposal,” says 
V Jayachandran, Technical Director of SIDCO phase I, Ranipet.