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Monday, November 30, 2020

Explained: How spike in ammonia levels in Yamuna affected Delhi water supply

The supply was restored back to normal by Sunday as the concentration of ammonia reduced, and the polluted water was mixed with cleaner water at various points in the DJB’s network.

Written by Shivam Patel | New Delhi | Updated: November 2, 2020 1:49:50 pm
Toxic foam floats on the surface of Yamuna River at Kalindi Kunj, in New Delhi (PTI)

Water supply was affected in parts of Delhi on Friday and Saturday after a spike in pollutants in the river Yamuna led to a temporary closure of two water treatment plants.

Ammonia levels in the river, flowing into Delhi from Haryana, had reached nearly 3 parts per million (ppm) on Thursday, almost six times above the acceptable limit of 0.5ppm, Delhi Jal Board (DJB) officials said. The supply was restored back to normal by Sunday as the concentration of ammonia reduced, and the polluted water was mixed with cleaner water at various points in the DJB’s network.

The plants’ closure

The DJB at present has the capacity to treat 0.9 ppm of ammonia in the raw water at nine water treatment plants. If the concentration is higher than this, then raw water is either diluted with fresh water from the Upper Ganga Canal or from the Munak Canal.

If the option to dilute the water is not available, the production capacity of plants is reduced or they are temporarily shut.

Ammonia levels increase frequently in the Yamuna in Delhi. In July, too, the concentration had reached 3ppm, as per DJB officials, who have credited this spike to industrial effluents and sewage released into the river in different parts of Haryana.

However, the rise in ammonia levels on Thursday coincided with the closure of the Upper Ganga Canal — which provides 250 million gallons per day (MGD) of water to the DJB’s Sonia Vihar and Bhagirathi plants, which are entirely dependent on this water.

The canal closes every year in October-November for 15 days to a month for maintenance. This year it has been shut since October 15, but until Friday was providing about 100-150 MGD of water to the two plants. The remaining share was being taken from an eastern bank of the Yamuna near the Wazirabad barrage.

delhi water supply, delhi water supply hit, delhi water supply update, Upper Ganga Canal, Upper Ganga Canal repair work, delhi water news, delhi city news Chadha at the Sonia Vihar WTP, Saturday. (Express Photo: Gajendra Yadav)

On October 29, when ammonia levels spiked, the Sonia Vihar and Bhagirathi plants had to be shut for some time until Yamuna water was diluted with Ganga water. They resumed functioning a few hours later with reduced treatment capacity.

Due to this, water was supplied on low pressure in parts of south, east, and north Delhi, while some places in these areas did not receive the regular supply on Friday and Saturday.

Another spike

The low amount of water being supplied through the Ganga canal was reduced further around 1 am on Saturday.

The share of water being taken from the Yamuna was then increased at the two plants to meet the shortfall from Ganga. However, at this time there was another sudden spike in the ammonia levels.

This was caused as freshwater from the Ganga was not available to mix with raw Yamuna water, which still had high concentration of ammonia, and an “ammonia ponding” had been made at the eastern bank of the river at a certain depth.

Because of this second spike, the two plants reduced their production capacity by 50% on Saturday morning.

“In order to address this problem, we deployed pumps to flush out the water with high levels of ammonia at the eastern bank and replace it with fresh water upstream of the river in Delhi,” a DJB official said.

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A boatman rows across Yamuna River as toxic foam floats on the river’s surface at Kalindi Kunj, in New Delhi (PTI)

“The Wazirabad barrage area — from where water is taken into the treatment plants — had high concentration of ammonia because it had collected there since Thursday, but upstream of the river, near Palla, the concentration was very low, upto 0.4 ppm,” a DJB official said.

Other water treatment plants of the DJB were also affected over the last few days by high levels of ammonia, but they had the option of mixing this raw water with fresh supply from the Munak canal — which brings Yamuna water from Munak area in Haryana.

The issue has prompted the DJB to request Uttar Pradesh authorities to finish the annual maintenance of the Upper Ganga Canal as soon as possible, as water demand increases during the festive season.

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