The continuous discharge of untreated wastewater from the Karuvadikuppam Sewage Treatment Plant (STP) into a canal meant originally meant for carrying rainwater in Lawspet, in gross violation of rules, poses a serious risk of contamination of water sources downstream and significant threat to environment and health of residents, environmentalists say.
Untreated greywater frothing and foaming at several points of the rainwater canal near the Narikoravar colony and adjacent to the Puducherry Airport remain a common sight.
The unchecked pollution by the STP maintained by the Drainage Division of the Public Works Department (PWD) goes against the claims made by the department that there is no illegal discharge of sewage in the city.
The discharge of untreated grey water is one of the starkest cases of pollution and official apathy, rue environmentalists.
According to Probir Banerjee, co-founder of PondyCan, a civil society organisation and member of Alliance for Good Governance (AGG), “The canal was supposed to carry excess rainwater during the monsoon. But the canal has now become an easy location for the authorities of the STP to conveniently dispose of their untreated grey water.
Thick foam is visible at many spots along the canal and the untreated water has been triggering a foul smell. This grey water meanders to the city to eventually flow out into the sea. The situation is similar all over the city and the authorities are using the ocean as a garbage dumpsite and ponds for sewage water to flow.”
Mr. Banerjee added, “The practice of discharging untreated grey water into the canal must be immediately stopped and authorities must ensure that this colossal amount of water being wasted is retreated and reused for various purposes.
The grey water gushing out and forming into a white frothy stream discharged is highly toxic. The possibility of toxic chemicals, causing foam to catch fire like what happened in Bellandur lake in Bengaluru cannot be ruled out here.”
Tests conducted by the Environmental Monitoring Service, a testing and research laboratory for water, soil and food products in Auroville last year had revealed that the biochemical oxygen demand (BOD)—a marker for organic pollutants in the wastewater discharged into the canal was found to be a whopping 3,192 mg/litre as against the permissible standards of 30 mg/litre on inland surface waters and 100 mg/litre for marine coastal areas.
The wastewater in the canal also had high levels of COD (chemical oxygen demand)—measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter. The level of COD at the canal is 6,590 mg/litre, which is highly above the prescribed limit of 250 mg/litre.
Residents living at the north-east of the STP have also expressed concern over untreated wastewater being let into the canal.
“The stench arising from the canal is unbearable as it passes through the houses. The foam also causes inconvenience to motorists as it keeps flying in the wind and putting them at risk,” said a resident.
A senior official of the PWD said the Department had received complaints about the illegal discharge of wastewater from the STP at Karuvadikuppam and Kanagan tank.
“Though the STP in Karuvadikuppam had a capacity of 17 million litres/day, only a few million litres were treated while the untreated grey water was being illegally discharged into drains and channels. The Department will be undertaking an inspection of the two STPs,” he said.
An official pointed out that the grey water forming into a white foam was due to the presence of surfactant in the grey water.
“As per norms, the treated grey water should be discharged through the Uppar drain and eventually let out into the sea. However, the PWD authorities have been conveniently discharging the untreated wastewater into drains.”
“Though repeated reminders have been sent to the Department to treat the wastewater before discharging it has failed to evoke any response. The PWD should ensure that special systems are put in place at the STPs to address this issue,” the official added.