One criterion that we omitted to mention while discussing sewage treatment is COD, or Chemical Oxygen Demand. It's a test that determines how much oxygen is needed to oxidize organic materials in a sewage sample using a potent oxidizing agent like potassium dichromate.
BOD vs. COD
The difference between COD and BOD, or Biochemical Oxygen Demand, is that BOD measures the amount of organic matter that can be biologically oxidized, whereas COD measures the amount of organic matter that can be chemically oxidized. The higher the BOD/COD ratio, the more oxygen-sucking capacity the discharged effluent has when discharged into receiving waters (oxygen is used biologically/chemically to break down the organic matter), and the greater the risk of biological life in those waters being harmed.
COD is usually larger than BOD
It is because chemical oxidation of organic substances is more efficient than biological oxidation. This includes substances that are harmful to biological life, which makes COD tests particularly valuable when assessing industrial sewage because BOD testing misses them.
COD has a significant benefit over BOD in that the test only takes about three hours, as opposed to five days for BOD testing.COD testing is the simplest technique to get immediate input on the polluting potential of sewage effluent, with the established ratio estimates used to infer the BOD. As technology advances, real-time monitoring of parameters including COD, SS, Ammonia, Total Nitrogen, and Phosphorus is now possible, allowing for greater operational control than ever before.
How is COD determined in wastewater?
In water, a high chemical oxygen demand suggests higher quantities of oxidizable organic matter and, as a result, less dissolved oxygen (DO). Organic contamination can cause critical DO depletion, which can destroy aquatic life forms.
In wastewater treatment, the benefits of chemical oxygen demand testing
Knowing the chemical oxygen demand in wastewater treatment has a number of advantages, including industrial and municipal clients in determining the optimum treatment method and the most efficient structure for their wastewater treatment facility is important.
COD in wastewater - what is it?
The amount of oxygen necessary to decompose all oxidizable chemicals in a determined sample of effluent is referred to as COD in wastewater. A COD test can be used to determine the COD value in wastewater.
Test for COD
COD vials are commonly used for measurement, and results are usually obtained in 2–3 hours.
Chemical oxygen demand wastewater treatment applications
COD has four significant applications in wastewater treatment:
1: To figure out how much oxidizable pollution is in the wastewater
2: As a metric for determining the overall quality of water
3: To evaluate the efficacy of wastewater treatment options
4: To find out how wastewater disposal affects the receiving ecosystem
Normal home sewage has an influence BOD of 300 mg/l, which is then treated to at least 25 mg/l (as per European standards) before being discharged to reduce polluting potential.
Most sewage treatment plants or wastewater treatment plants are designed to achieve a minimum BOD level of 25 mg/l, however significantly lower BOD values as low as 5 mg/l can be obtained if requested.
Furthermore, in a constant wastewater flow, the COD/BOD ratio is usually stable. Normal home sewage has an influence COD of 600–900 mg/l, and it is treated to at least 75–100 mg/l before being discharged to reduce polluting potential.
Most sewage treatment systems, are designed to achieve a COD level of 75 mg/l at a minimum, however COD values as low as 10-15 mg/l can be attained if specified based on regular home sewage.
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