The number of polluted stretches of the country’s rivers has increased to 351 from 302 two years ago, and the number of critically polluted stretches — where water quality indicators are the poorest — has gone up to 45 from 34, according to an assessment by the Central Pollution Control Board (CPCB).
Based on the recommendations of the National Green Tribunal, the CPCB last month apprised the States of the extent of pollution in their rivers.
Increase in numbers: The number of polluted stretches of the country’s rivers has increased to 351 from 302 two years ago, and the number of critically polluted stretches — where water quality indicators are the poorest — has gone up to 45 from 34.
Several of the river’s stretches — in Bihar and Uttar Pradesh — are actually far less polluted than many rivers in Maharashtra, Assam, and Gujarat. These three States account for 117 of the 351 polluted river stretches.
The most significant stretches of pollution highlighted by the CPCB assessment include the Mithi river — from Powai to Dharavi — with a BOD (Biochemical Oxygen Demand) of 250 mg/l; the Godavari — from Someshwar to Rahed — with a BOD of 5.0-80 mg/l; the Sabarmati — Kheroj to Vautha — with a BOD of 4.0-147 mg/l; and the Hindon — Saharanpur to Ghaziabad — with a BOD of 48-120 mg/l.
The CPCB, since the 1990s, has a programme to monitor the quality of rivers primarily by measuring BOD, which is a proxy for organic pollution — the higher it is, the worse the river.
The health of a river and the efficacy of water treatment measures by the States and municipal bodies are classified depending on BOD, with a BOD greater than or equal to 30 mg/l termed ‘priority 1,’ while that between 3.1-6 mg/l is ‘priority 5.’
The CPCB considers a BOD less than 3 mg/l an indicator of a healthy river.
Central Pollution Control Board (CPCB):
Central Pollution Control Board (CPCB), the statutory organization, was constituted in September 1974 under the Water (Prevention and Control of Pollution) Act, 1974. Further, CPCB was entrusted with the powers and functions under the Air (Prevention and Control of Pollution) Act, 1981.
To promote cleanliness of streams and wells in different areas of the States by prevention, control, and abatement of water pollution.
To improve the quality of air and to prevent, control or abate air pollution in the country.
Biochemical oxygen demand (Bod):
Biochemical oxygen demand is the amount of oxygen required for the microbial metabolism of organic compounds in water.
BOD value is most commonly expressed in milligrams of oxygen consumed per liter of the sample during 5 days of incubation at 20 °C.
BOD can be used as a gauge of the effectiveness of wastewater treatment plants.