Wastewater contains chemicals in the form of organics as well as inorganics, apart from gases.

The biological oxygen demand, ie, BOD in wastewater, is a measure of the quantity of bio-organic substances in wastewater. These can be in the form of fat, oils, carbohydrates and proteins. BOD also helps determine the quantum of organic chemicals contained in wastewater that are synthetic and biodegradable.

Does your effluent treatment plant stabilize organic matter efficiently? You can find out by comparing the BOD of the treated wastewater with the BOD in wastewater that is untreated.

Another useful measure of biological oxygen demand is chemical oxygen demand, or COD. COD can help gauge the quantum of both biodegradable and non-biodegradable organics.

Find out the BOD5 of the wastewater (the BOD of wastewater that is five days old). When you divide BOD5 by COD, you get a measure of how easily your treatment plant is able to treat wastewater.

A BOD5/COD ratio that is equal to or higher than 0.5 indicates fast biological decomposition.

Any ratio above 0.2 indicates that the biological treatment of the wastewater influent is possible. But when the ratio is less than 0.5, the process will be relatively slow, as the acclimatization of the microorganisms that help in the degradation process takes time.

Industrial wastewater usually has a BOD5/COD ratio of less than 0.5. An exception to the rule can be found in industries that manufacture/ process food or beverages, where the said ratio is much higher.