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No Delhi drain met pollution standard: Data
The report also found that the BOD level at Najafgarh drain, which carries nearly 69% of Delhi’s total sewage into the Yamuna, has continued to rise for the third consecutive month
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None of the 18 major drains in Delhi met the biological oxygen demand (BOD) limit of 30mg/litre or less in the month of March, the latest water analysis report released by the Delhi Pollution Control Committee (DPCC) showed. This indicates that considerable efforts are still required to control sewage and industrial effluents flowing through these drains into the Yamuna.
The report also found that the BOD level at Najafgarh drain, which carries nearly 69% of Delhi’s total sewage into the Yamuna, has continued to rise for the third consecutive month and was recorded at 58mg/litre in March. In February, it was 55mg/litre, and 53mg/litre in January.
BOD is considered an indicator of how polluted the water is in a river or a drain. It represents the amount of oxygen used up when organic matter, such as sewage, is broken down, thus representing the quantity of pollutants. When high levels of oxygen are used up in the breakdown of pollutants, the dissolved oxygen for survival of aquatic life reduces.
A DPCC official said that over the last one year, the overall trend at most drains, including Najafgarh, has shown a decrease in the demand for oxygen. He added that minor fluctuations are expected till smaller drains get trapped.
Trapping is a process where the drain is connected to a sewage treatment plant (STP). The report said that both Najafgarh and Shahdara – two of Delhi’s biggest drains – are too large to be trapped. It said that only their supplementary drains are being trapped under the interceptor sewage project. DJB and the environment department have set a target to trap the remaining three of the major drains by September 2023, the latest report said.
The highest BOD level, according to the DPCC report in March, was 60mg/litre at Sonia Vihar and Sahibabad drains. This was followed by Najafgarh and Shahdara drains at 58mg/litre. The lowest BOD reading was recorded at the Shastri Park drain (40mg/litre).
The other parameters assessed include total suspended solids (TSS) and chemical oxygen demand (COD). While 10 out of 18 drains met the TSS threshold of 100mg/litre, indicating the volume of suspended particle in these drains was under control, three out of 18 met the COD threshold of 250mg/litre or less, indicating a lack of sufficient oxygen in these drains for chemical reactions like oxidation.
While no drain met the BOD limit in February, the lowest level was recorded at 38 mg/litre at the Shastri Park drain. In January, two drains met the limit, with drain number 14 recording the lowest reading of 21 mg/litre. “In August 2022, the BOD was as high as 75 mg/litre at the Najafgarh drain. There is a gradual improvement and this will continue as more sewage gets trapped,” the official said, on condition of anonymity.
Based on the latest progress report shared by agencies with the National Green Tribunal (NGT) appointed high-level monitoring committee (HLC) in March, at least 11 drains in Delhi have been trapped completely, including the two drains with the highest BOD levels. Two other drains have been partially trapped and five are yet to be trapped, including the drains at Najafgarh, Shahdara, Barapullah, Maharani Bagh, and Mori Gate, the report said.
Agencies such as DPCC, the environment department, DJB, the irrigation and flood control department, municipal corporation of Delhi, Delhi development authority, public works department, Delhi state industrial and infrastructure development corporation, New Delhi municipal corporation and Delhi urban shelter improvement board are involved in cleaning the Yamuna river.
Data shared by the Delhi environment department with the HLC in January showed that the Najafgarh drain accounts for 68.71% of wastewater being discharged into the Yamuna. The Shahdara drain, the second biggest polluter, accounts for 10.9% followed by the Barapullah drain at 3.15%.
Delhi lieutenant governor VK Saxena, who is also head of the HLC, also held a review meeting on the Najafgarh Lake on Wednesday, forming a nine-point plan for its revival. The Najafgarh Lake ultimately connects with the Yamuna through the Najafgarh drain.
An LG House official said that Saxena and the HLC took note of the BOD fluctuations at the Najafgarh drain. “What is encouraging is that it remains consistently below 75 mg/litre, which was the reading when the cleaning of the drain began in August 2022. These minor fluctuations will happen until all supplementary drains connected to it are trapped and the sewer lines are cleaned. Both works are currently in progress.”
The Delhi government and DJB did not respond to requests for comment.
Manoj Misra, convener of the Yamuna Jiye Abhiyaan, said if trapped drains are not meeting the BOD limit, it indicates that some smaller supplementary drains have not been accounted for by the agencies.
“It is either possible that some drains were missed when they were being connected to the STPs or that the STPs are not functioning at the optimal level. Since the interceptor sewage project was planned, a lot of new unauthorised colonies came up, subsequently changing the ways in which waste entered these drains,” he said. Misra added that the data indicates agencies need to revisit the drains that are completely trapped too and examine the situation.
