BOD and COD

BOD or Biochemical/Biological Oxygen Demand is a characteristic that express the amount of dissolved oxygen needed by microorganism (usually bacteria) to decompose or break down the organic matter under anaerobic condition (Umaly and Cuvin, 1998; Metcalf and Eddy, 1991). Reiterated again by Boyd (1990), that organic material decomposed in BOD is organic material that is ready to decompose (readily decomposable organic matter). Mays (1996) defines BOD as a measure of the amount of oxygen used by microbial populations contained in waters in response to the entry of decomposed organic matter. From these notions it can be said that although the BOD value states the amount of oxygen, but for simplicity it can also be interpreted as a description of the amount of biodegradable organics in the waters.

Chemical Oxygen Demand (COD) is a second method oORPf estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. test uses a strong chemical oxidizing agent (potassium dichromate or potassium permanganate) to chemically oxidize the organic material in the sample of wastewater under conditions of heat and strong acid, so that all kinds of organic materials, both those that are easy to decompose or are easily complex and difficult to decompose, will oxidize. It has the disadvantage of being completely artificial but is nevertheless considered to yield a result that may be used as the basis upon which to calculate a reasonably accurate and reproducible estimate of the oxygen-demanding properties of a wastewater.

The COD test is often used in conjunction with the BOD test to estimate the amount of nonbiodegradable organic material in a wastewater. In the case of biodegradable organics, the COD is normally in the range of 1.3 to 1.5 times the BOD, and it could be that the BOD value is the same as the COD, but the BOD cannot be greater than the COD. When the result of a COD test is more than twice that of the BOD test, there is good reason to suspect that a significant portion of the organic material in the sample is not biodegradable by ordinary microorganisms. As a side note, it is important to be aware that the sample vial resulting from a COD test can contain leachable mercury above regulatory limits. If such is the case, the sample must be managed as a toxic hazardous waste.