A significant drop in industrial wastewater discharges and agricultural run-offs amid the lockdown,  has cleaned water marginally of otherwise polluted Ganga, the Central Pollution Control Board (CPCB) has said in its post-lockdown analysis of the river water quality.

The improved water quality comes on the back of a marginal increase in dissolved oxygen (DO) levels and reduced nitrate.DO is a crucial indicator of water quality and thus provides a gauge of how well the water can support aquatic plant and animal life. A higher value indicates better water quality

It is attributed to absence of industrial wastewater discharge, agricultural runoff and increased fresh water flow in the river.

Though the improvement was “not substantial” as there was no significant reduction in other indicators- biochemical oxygen demand (BOD) and chemical oxygen demand (COD) and concentrations of ammoniacal nitrogen, which is seen to have gone up in certain locations. both indicators of the amount of oxygen necessary to break down organic and inorganic pollution.

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                 Biological oxygen demand (BOD) generally represents how much oxygen is needed to break down organic matter in water; 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.

                 COD refers to the chemical oxygen demand, which measures the amount of DO, required by the decomposition of organic matter and the oxidation of inorganic chemicals like ammonia and nitrite.

The greater the BOD in a particular water body, the lesser oxygen is available for the aquatic life forms in that particular water body. Aquatic life forms would be stressed, suffocate and ultimately die due to high BOD.It is also used in wastewater treatment to decompose organic wastes by aerobic organisms.

BOD and COD measurements are taken to determine the pollution level of wastewater. COD value is always greater than the BOD value of a particular water body.

BOD measures the oxygen demand for the decomposition of organic material by the microbes in the wastewater. COD measures the oxygen demand for the decomposition of both organic and inorganic materials in wastewater. This is the main difference between BOD and COD.