The unchecked flow of untreated industrial effluent into rivers in Gujarat has led to increasing pollution in the Sabarmati, Mahisagar, Narmada, Vishwamitri and Bhadar.
- If the chemical oxygen demand (COD), which indicates organic pollutant load, is higher than 250 mg per litre, then it should not be released into the rivers.
- Most of the Gujarat rivers where the effluents are dumped into, the COD level is in the range of 700 to 1000 mg per litre.
- While Dissolved Oxygen (DO) level in perennial rivers like Mahisgar should be in the range of 6 to 8 mg per litre, it is actually below 2.9 mg per litre
- According to data from the Ministry of Environment and Forest (MoEF), the Sabarmati is among the most polluted rivers in the country.
- Gujarat ranks fourth among the top five States with highly polluted rivers, with as many as 20 rivers in the critically polluted category.
BOD, COD and DO differences
- Dissolved Oxygen (DO) level: Indicates the health of a river. Do is the amount of oxygen that is present in water. Water bodies receive oxygen from the atmosphere and from aquatic plants. Running water, such as that of a swift moving stream, dissolves more oxygen than the still water of a pond or lake.
- COD or Chemical Oxygen Demand: It is the total measurement of all chemicals in the water that can be oxidized. The COD test is often used to monitor water treatment plant efficiency
- Biochemical oxygen demand (BOD): It represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.
(Source: The Hindu, NASA and EU)
