The Yamuna recorded a marked improvement in water quality in August, with faecal coliform levels falling sharply across monitoring locations in Delhi compared with July, even as high Biological Oxygen Demand (BOD) readings showed that the river continues to face a significant pollution burden.
The latest Delhi Pollution Control Committee (DPCC) data showed substantial month-on-month declines in faecal coliform, an indicator of sewage contamination, at monitoring points along the river. The improvement could indicate a reduction in the concentration of untreated sewage entering the Yamuna, although increased river flow and dilution caused by monsoon rainfall may also have contributed to the lower readings.
Despite the improvement, five of the readings remained above the permissible faecal coliform limit of 2,500 Most Probable Number per 100 millilitres (MPN/100 ml). The desirable level is 500 MPN/100 ml.
Sharp fall at key points
One of the steepest improvements was recorded at Asgarpur, where faecal coliform fell from 320,000 MPN/100 ml in July to 36,000 MPN/100 ml in August. While representing a sharp decline, the August reading was still more than 14 times the permissible limit.
At ISBT Bridge, the level declined from 170,000 MPN/100 ml in July to 35,000 MPN/100 ml in August.
ITO Bridge recorded a fall from 120,000 MPN/100 ml to 17,000 MPN/100 ml, while at Okhla Barrage, faecal coliform declined from 110,000 MPN/100 ml in July to 23,000 MPN/100 ml in August.
At Nizamuddin Bridge, the level dropped substantially to 13,000 MPN/100 ml from 130,000 MPN/100 ml in July.
The upstream monitoring locations recorded considerably lower contamination. At Palla, faecal coliform declined from 2,100 MPN/100 ml in July to 1,400 MPN/100 ml in August. At Wazirabad, it fell from 3,500 MPN/100 ml to 1,100 MPN/100 ml.
Both Palla and Wazirabad were therefore within the permissible limit of 2,500 MPN/100 ml in August, although they remained above the desirable level of 500.
BOD remains elevated
The improvement in faecal coliform was accompanied by lower BOD readings compared with July, but several stretches continued to breach the prescribed water-quality criterion.
BOD measures the amount of dissolved oxygen required by microorganisms to break down organic matter in water. Higher BOD generally indicates a greater concentration of organic pollution and lower water quality.
In August, BOD readings across the monitored stretch ranged between 3 mg/l and 28 mg/l, against the prescribed maximum of 3 mg/l.
The highest BOD level was recorded at ISBT Bridge at 28 mg/l, indicating that significant organic pollution persists despite the improvement in other indicators.
Drains remain problem
The DPCC monitors Yamuna water quality by collecting samples at seven locations — Palla, Wazirabad, ISBT Bridge, ITO Bridge, Nizamuddin Bridge, Okhla Barrage and Asgarpur at Kidwali in Haryana.
Samples are tested for parameters including BOD, dissolved oxygen, chemical oxygen demand, pH and faecal coliform to assess the extent and nature of pollution.
The pollution watchdog’s August data on wastewater quality in Delhi’s major drains also points to continuing pressure on the river.
Several drains discharging into the Yamuna, as well as supplementary drains connected with the Najafgarh drain system, recorded high BOD and Total Suspended Solids (TSS) levels.
Untreated and inadequately treated sewage entering through Delhi’s drain network has long been a major contributor to pollution in the river.
Monsoon effect
The sharp improvement between July and August needs to be viewed alongside seasonal changes in the Yamuna’s flow. Higher rainfall and increased freshwater discharge during the monsoon can dilute pollutants and temporarily improve several water-quality indicators.
The August readings nevertheless provide a significant month-on-month improvement, particularly at some of the river’s most polluted downstream monitoring locations.
However, the persistence of high faecal coliform concentrations at five monitoring points, elevated BOD and poor wastewater quality in several drains shows that the underlying pollution challenge remains.