Biological oxygen demand is calculated to know— wastes –
**Core Concept**
Biological oxygen demand (BOD) is a measure of the amount of oxygen required for the aerobic decomposition of organic matter by microorganisms in water. It is an important parameter in assessing the quality of water, particularly in wastewater treatment and aquatic ecosystems.
**Why the Correct Answer is Right**
BOD is calculated to determine the amount of organic waste present in water, which can be hazardous to aquatic life. The BOD test measures the amount of oxygen consumed by microorganisms as they break down organic matter over a specified period, usually five days. This helps to assess the level of pollution and the effectiveness of wastewater treatment processes.
**Why Each Wrong Option is Incorrect**
**Option A:** BOD is not directly related to chemical oxygen demand (COD), although both parameters are used to assess water quality. COD measures the total amount of oxygen required to break down organic and inorganic matter, whereas BOD specifically measures the oxygen required for aerobic decomposition of organic matter.
**Option B:** BOD is not a measure of the amount of oxygen present in water. It is actually a measure of the amount of oxygen consumed by microorganisms during decomposition, which is an important distinction.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that BOD is an indirect measure of organic pollution, and it can be affected by factors such as temperature, pH, and the presence of toxic substances.
**Correct Answer: D. Organic wastes.**