Fewer polluted river stretches but worst stretches unchanged

Context

A report by Central Pollution Control Board (CPCB) says that the number of polluted stretches in India’s rivers has fallen, but the number of most polluted stretches is practically unchanged.

Key Findings:

The decline in polluted Stretches: The number of polluted stretches in India’s rivers has fallen from 351 in 2018 to 311 in 2022.
Unchanged polluted stretches: The number of polluted river stretches categorized in ‘Priority I & II’ is almost unchanged.
Biochemical Oxygen Demand (BOD) exceeding 3.0 mg/L (milligram per litre) is identified as a polluted location.
Two or more polluted locations identified on a river in a continuous sequence are considered a “polluted river stretch.”
A BOD less than 3 mg/L means the river stretch is fit for ‘Outdoor Bathing.’

There are five such categories:

· Priority 1: Stretches with a BOD exceeding 30 mg/L are considered ‘Priority 1,’ meaning, the most polluted and thus needing the most urgent remediation.

· ‘Priority 2’ indicates a BOD of 20-30 mg/L.

· ‘Priority 3’ indicating 10-20 mg/L

· ‘Priority 4’ indicating 6-10 mg/L

· ‘Priority 5’ indicating 3-6 mg/L

Biological Oxygen Demand (BOD):

Biological Oxygen Demand is the amount of dissolved oxygen needed by microorganisms to decompose organic matter (waste or pollutants) under aerobic reaction (in the presence of oxygen).
The more organic matter there is (e.g., in sewage and polluted bodies of water), the greater the BOD.
Greater the BOD, the lower the amount of dissolved oxygen available for higher animals such as fish.
The BOD is therefore a reliable gauge of the organic pollution of a water body.
One of the main reasons for treating wastewater prior to its discharge into a water resource is to lower its BODe., to reduce its need for oxygen and thereby lessen its demand from the streams, lakes, rivers, or estuaries into which it is released.

About Central Pollution Control Board (CPCB):

CPCB is a statutory organization that was constituted in September 1974 under the Water (Prevention and Control of Pollution) Act, 1974.
It was also entrusted with the powers and functions under the Air (Prevention and Control of Pollution) Act, 1981.
It serves as a field formation and also provides technical services to the Ministry of Environment, Forest and Climate Change of the provisions of the Environment (Protection) Act, 1986.
The CPCB network monitors water quality at 4,484 locations in 28 States and seven Union Territories including rivers, lakes, creeks, drains, and canals.
Principal Functions of the CPCB:
- CPCB is monitoring the water quality in India under National Water Quality Monitoring Programme.
- To promote the 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.

Identification Of Polluted River Stretches:

CPCB is monitoring the water quality in India under National Water Quality Monitoring Programme. The water quality data is analyzed and monitoring locations exceeding the water quality criteria are identified as polluted locations with respect to risk. Priority levels of polluted stretch are based on the risk.

Risk is defined as =Frequency of Violation of Criteria X Consequence (Magnitude)

The degree of violation is with respect to water quality criteria for drinking water sources with conventional treatment with respect to BOD (Annexure-I- Water Quality Criteria).
The polluted locations in a continuous sequence are defined as polluted river stretches.

Reasons for Polluted Rivers: