Latest CPCB data shows that the no. of critically polluted river stretches is on the rise

Latest CPCB data shows that the no. of critically polluted river stretches is on the rise

 
How much clean are our rivers? Latest data indicates a negative trend. A report by the Central Pollution Control Board (CPCB), which was released in September this year, reveals that in total there were 45 river stretches across the country in 2016-17, where water quality is found to be the worst. In 2014-15, however, the total number of such river stretches was just 34.

Technically speaking, the value of biochemical oxygen demand (BOD) of the water flowing in these river stretches exceed 30 milligram (mg) per litre (l). For example, the maximum value of BOD of water found in the Yamuna river stretch between Wazirabad and Asgarpur ranges from 9 mg/l to 80 mg/l, according to the new CPCB report.

The latest report indicates that there were 16 river stretches across the country in 2016-17, where BOD value is reported to be lying between 20 mg/l and 30 mg/l. It has been observed that there were 43 river stretches, where BOD value of water is between 10 mg/l and 20mg/l, although in 72 river stretches, BOD value is between 6 mg/l and 10 mg/l. The CPCB has found that in 175 river stretches, BOD value of water is between 3 mg/l and 6 mg/l. Please consult table-1 for details.

Table 1: Priority-wise number of polluted river stretches as per 2015 and 2018 CPCB reports

Table 1 Priority wise numbet of polluted river stretches
 
Source: River Stretches for Restoration of Water Quality: State-wise and Priority-wise, CPCB, September, 2018, please click here to access
 
River Stretches for Restoration of Water Quality, CPCB, February, 2015, please click here to access 
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It could be seen from table-1 that the total number of critically polluted river stretches has increased from 302 to 351 between 2014-15 and 2016-17. The total number of river stretches, where BOD value exceeds 30 mg/l, has increased from 34 to 45 over this time span, as already mentioned above.

The latest CPCB report, which is based on statistical analysis of water quality data under the National Water Quality Monitoring Programme for 2016-17, says that in 31 states and Union Territories (UTs) rivers and streams have not met water quality standards. Maharashtra (53) has the highest number of polluted river stretches (from Priority-I to Priority-V), followed by Assam (44), Madhya Pradesh (22), Kerala (21), and Gujarat (20). Please check table-2 for details.

The highest number of river stretches, where water quality is the worst in terms of BOD value (viz. greater than 30 mg/l that falls under Priority-I), is found in Maharashtra (9), followed by Gujarat (5), Tamil Nadu & Uttar Pradesh (both 4), Assam, Madhya Pradesh & Uttarakhand (3 each) and Haryana, Meghalaya & Punjab (2 each).

Table 2: State-wise & priority-wise number of polluted river stretches
 
Table 2 State wise & priority wise number of polluted river stretches
 
Source: River Stretches for Restoration of Water Quality: State-wise and Priority-wise, CPCB, September, 2018, please click here to access

It may be noted that polluted locations in a continuous sequence is defined by the CPCB as polluted river stretches, and they are categorised in five different priority classes based on BOD concentration viz. Priority I: BOD value > 30 mg/l; Priority II: BOD between 20 mg/l & 30 mg/l; Priority III: BOD between 10 mg/l & 20 mg/l; Priority IV: BOD between 6 mg/l & 10 mg/l; and Priority V: BOD between 3 mg/l & 6 mg/l.

About BOD

Water quality in river stretches is judged from the value of BOD. The higher the value of BOD, the lower is the concentration of dissolved oxygen, which is available for higher animals such as fishes. The value of BOD goes up when there is more organic matter in water such as in untreated sewage water. The value of BOD concentration gives one an idea about the degree of organic pollution of water resources. Its value can also be used as an estimate of the effectiveness of wastewater treatment plants.

A standardized laboratory test of BOD measures oxygen requirement for aerobic oxidation of decomposable organic matter and certain inorganic materials in water, polluted waters and wastewater under controlled conditions of temperature and incubation period. The value of BOD is expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C.

References

River Stretches for Restoration of Water Quality: State-wise and Priority-wise, CPCB, September, 2018, please click here to access 

River Stretches for Restoration of Water Quality, CPCB, February, 2015, please click here to access 

Guide Manual: Water and Wastewater Analysis, please click here to access
 
Biochemical Oxygen Demand (BOD), Encyclopaedia Britannica, please click here to access (accessed on 8th October, 2018)

              
Image Courtesy: UNDP India








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