Domestic sewage comprises 80% of pollution load and continues to get discharged into the river
With industries shut due to the novel coronavirus disease (COVID-19) lockdown, national capital city’s residents have been sharing photographs of a ‘cleaner Yamuna’.
Delhi Jal Board (DJB) Vice-Chairman Raghav Chaddha recently said there was an improvement in water quality due to a dip in industrial pollutants being discharged into the river.
While several reports about improvement in the river’s health did the rounds on social media, how reliable are they?
Industrial pollution makes up for only 10-20 per cent of pollution load — the rest comes from domestic sewage, which has not seen any major decline as households continue to dispose waste.
This could mean that closure of industries may not have had a major impact on pollution levels in the Yamuna.
Coliform bacteria that moves into rivers through untreated sewage also continues to pollute the river. A 2016 assessment of river Yamuna showed faecal coliform count as high as 92 lakh most probable number (mpn) per 100 millilitres in areas like Nizamuddin and Okhla Bridge.
River water can be considered fit for bathing if faecal coliform count is under 500 and 2,500 mpn per 100 ml, according to government norms.
“Areas like Palla and Nizamuddin have a high faecal coliform count that has not come down. Yamuna is only 50 per cent sewered and lot of untreated sewage still continues to drain in it,” said Sushmita Sengupta, programme manager (Water), Centre for Science and Environment (CSE).
She added that the stretch near industrial hotspots could be doing better as factories that contributed to the pollution load are shut.
There is no real-time or comparative data to measure the impact of lockdown on pollution in Yamuna so far.
The Central Pollution Control Board (CPCB) has already collected samples from four-five points on the river stretch in Delhi and are analysing it to see what difference the shutdown made, according to Prashant Gargava, member secretary, CPCB.
“There are other factors that are helping relieve water pollution, like release of the fresh water. The DJB has been releasing some water in the river, which may have helped dilute pollutants. We will know more once the report is prepared,” he said.
Domestic sewage is the main cause of contamination for the Ganga as well. Around 2,723.30 million litre per day (MLD) sewage is generated every day by 50 cities located along the river.
According to CPCB’s real-time water monitoring data, out of the 36 monitoring units along the Ganga, 27 had water fit for bathing. The data found that water was also fit for drinking at some locations where biochemical oxygen demand (BOD) was less than three milligram per litre (mg/l).
However, CPCB’s real-time data has its own limitations and may not give a complete picture.
The BOD measurement in real time may reflect errors, according to Debadatta Basu, advisor at CSE.
“It’s tricky to measure BOD. A 10-15 per cent error can be a big error. In classical method, the error is very less, but we are now measuring through spectroscopic method which has some errors in real time," he said, adding faecal contamination is not measured in real-time.
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