જૈવરાસાયણિક ઑક્સિજન જરૂરિયાત $(BOD)$ એટલે શું ? 

Biochemical oxygen demand is the amount of oxygen required by bacteria to decompose organic matter in a certain volume of sample of water. Clean water would have a $BOD $ value of less than $5$ $ppm$, whereas highly polluted water has a $BOD$ value of $17$ $ppm$ or more.