Every day, sewage from thousands of households and commercial buildings is taken through pipelines that run for a length of 4,500 kilometres, to 253 pumping stations and treated at 12 sewage treatment plants (STPs, three each at Kodungaiyur, Koyambedu, Nesapakkam and Perungudi), before being let out into the nearest waterbody or reused for gardening and other purposes, claims the Chennai Metro Water Supply and Sewage Board (CMWSSB).
This, however, is refuted by activists in the city. According to them, Chennai generates much more than the 580 MLD (million litres per day) of sewage as claimed by the board, even above the installed capacity of 727 MLD, adding that the STPs were letting out untreated waste to the water bodies.
Extrapolating information from the water supplied, number of households and other data, city-based Arappor Iyakkam’s audit last year revealed the gross discrepancy between the Metro Water’s numbers and their calculations.
“Metro Water puts the generation at 1,000 MLD, though they don’t have an official number. Based on our estimates – calculated by population and water supply data – we estimated that the city generates at least 1,500 MLD, which is still conservative.
The generation may be much higher,” said Jayaram Venkatesan, convenor of the organisation. The numbers are also inconsistent when it comes to the quantity of sewage being treated. On auditing the sewage treatment plants, Jayaram and his team found the Kodungaiyur and Nesapakkam plants in a bad condition.
“Accounting for the dysfunctional units of the sewage treatment plants (STPs), only 430 MLD is treated in contrast to Metro Water’s claim of 522 MLD,” he added. What happens to the rest of the sewage?
“We have evidence of raw (or partially treated) sewage being directly let into waterbodies from the pumping stations. For example, from the RK Nagar North Pumping Station, we found partially treated sewage being let out. Similar incidents occur at Cooum river near Thideer Nagar,” said Jayaram.
If the generation itself is higher, as the activists allege, then the actual quantum of raw sewage dumped into waterbodies, too, is critically high – Arappor’s report alleged 1,000 MLD of untreated sewage was being let out into the city’s waterbodies.
Hemraj V, whose residence is a few kilometres from the RK Nagar North pumping station, said he has seen partially treated sewage dumped into the Buckingham Canal barely a month ago.
“It seems the sewage from the households is collected and then dumped into the canal. When we questioned the officials, they hardly gave us a response. The sewage inflow stinks the neighbourhood, in addition to polluting the environment,” said the youngster, employed at a marketing firm. Dumping sewage in waterbodies has far-reaching consequences.
“Raw sewage dumped into the Buckingham Canal, for instance, flows into the Adyar river, severely polluting the waterbody,” said environmentalist Arun Krishnamoorthy, whose NGO Environmentalist Foundation of India (EFI) conducts regular clean-up of waterbodies.
“Even lakes like Adambakkam lake are polluted due to direct inflow of sewage. We need a robust infrastructure to treat and efficiently reuse sewage. There is a huge gap between the quantum of liquid waste generated and the current infrastructure,” he added.
New STPs are under construction at Tiruvottiyur, Sholinganallur (I and II) at an estimated cost of Rs 126 crores, augmenting the capacity by 103 MLD. They are expected to be functional by January 2019. Satyabrata Sahoo, who holds the additional charge of Metro Water Managing Director, said the existing STPs have the capacity to handle present generation.
“There is also excess capacity at certain plants, like the Koyambedu STP. In addition, we are adding more facilities such as specialised RO plants at Kodungaiyur for 45 MLD and other initiatives,” he said.
While a simple visit to Buckingham Canal or Cooum is sufficient to realise the sewage inflow, a more detailed study had shown that Marina beach is the most polluted in terms of faecal coliform (FC) presence, an indicator of sewage. This was reported by the National Centre for Coastal Research (NCCR).
“Large quantities of nutrients released into the coastal water through the sewage wastewater through Ennore, Cooum, Adyar and Muthukadu mouth, resulting nutrient enrichment and stimulating algal growth, depletion of dissolved oxygen, bioaccumulation of organic and inorganic compounds, and alteration of trophic interactions among both aquatic flora and fauna.
Elevated nutrient levels also result in excessive growth of algal blooms, some of which may result in production of algal toxins. The algal toxins are risks for water and seafood quality and safety. Effects arising from bacterial pollution are many and they involve public health, as well as social and economic implication,” said the report.
The study stated that Marina beach had the highest level of microbial contamination followed by Elliot’s, Tiruvanmiyur, Ennore and Kovalam beaches, which the NCCR scientists pinned on sewage inflow.
“The pollution is caused by the rivers, as untreated sewage is released into them because most of the treatment plants are not functional,” said Pravakar Mishra, scientist, NCCR, adding that Marina is worst-affected because it is trapped between Cooum and Adyar rivers, both critically polluted by sewage inflow. This raises several important questions – if there is no proper estimate of sewage generation, what is the Metro Water’s vision to address the existing gap between generation and treatment?
“We have suggested an online monitoring system which can be tracked by the headquarters. This will give an idea on the quantity and quality of treatment,” added Jayaram.