What is Biochemical Oxygen Demand (BOD)?
The BOD is an important measure of water quality. It is a measure of the amount of oxygen needed (in milligrams per liter or parts per million) by bacteria and other microorganisms to oxidize the organic matter present in a water sample over a period of 5 days. The BOD of drinking water should be less than 1. That of raw sewage may run to several hundred. It is also called the “biological†oxygen demand. What is Primary Treatment? The simplest, and least effective, method of treatment is to allow the undissolved solids in raw sewage to settle out of suspension forming sludge. Such primary treatment removes only one-third of the BOD and virtually none of the dissolved minerals. Attempts to use digested sludge as a fertilizer have been hampered by its frequent contamination by toxic chemicals derived from industrial wastes. What is Secondary Treatment? Many treatment plants pass the effluent from primary treatment to secondary treatment. Here the effluent is brought in contact with ox
