Checking water pollution is critical not just to ensure a clean environment, but also to combating water scarcity and improving the availability of clean water for industrial use. For effective and efficient filtration, the nature and quantity of pollutants in the water must first be assessed. This in turn determines the design and capacity of the water treatment plant required. BOD and COD are the keys to measuring the pollution level of water.
What is BOD
The full form of BOD is Biological Oxygen Demand. BOD is denoted the amount of oxygen required for the bacteria in a natural water body to decompose organic matter at a specific temperature. If the BOD is higher, it means more of the dissolved oxygen in the rivers or lakes will go towards decomposing biological waste. This will endanger aquatic life.
The higher the BOD, the higher the pollutants present in water.
The BOD test is conducted in two parts. First comes the immediate measurement of dissolved oxygen (initial test) and second, is the measure of dissolved oxygen after 5 days of the incubation period (final).
BOD test has some serious limitations
It takes a long time
The long incubation time required for the BOD test often creates a problem. Till the time you have measurements for a sample, the water from which the sample was taken could have left your plant, going far away down the river.
Difficulty in ensuring consistency
BOD tests only provide an estimate of oxygen that will be required by microbes to decompose the biological matter in water. Some toxic substances in wastewater could prevent bacterial growth. Industrial wastewater often contains cyanides, heavy metal ions, and other substances which are toxic for microorganisms. When microbes are poisoned by these substances, they are unable to oxidize biological matter. This renders the entire BOD test ineffective in measuring the organic pollution in water.
What is COD?
The full form of COD is Chemical Oxygen Demand. COD is the amount of oxygen required to oxidize organic matter using a chemical oxidant. The COD test involves using chemical oxidants that oxidize both organic as well as inorganic matter in wastewater. The COD yields a higher concentration than BOD because BOD only processes biological matter. As opposed to 5 days for the BOD test, COD only takes a few hours, and yields more accurate results. The popularity of COD has been growing since the 1980s. More and more businesses are now replacing the BOD with the COD Water Treatment test.
The correlation between BOD and COD Water Treatment
The BOD and COD tests are conducted partially and the COD data can then be used to target a specific BOD range. This eliminates the need for multiple BOD delusions. You could calculate the ratio of COD: BOD in the wastewater to improve your process efficiency.
To calculate the ratio, conduct COD and BOD tests independently on several wastewater samples. Next, divide the COD concentration by the BOD concentration for each water sample and average the results. The COD: BOD ratio is constant for a particular wastewater sample. For instance, it should generally be 2:1 for the food industry, while the die industry shows a slightly higher ratio of 5:1.
Once you learn the average COD:BOD ratio for your wastewater, a quick COD test should enable you to predict the BOD levels with much accuracy.
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