What are BOD and COD analyzers?
The Biochemical Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD) examinations are among the primary techniques used in the measurement of the concentration of organic matter in a sample of water. Although these two tests are quite dissimilar, they are typically combined to determine the amount of nonbiodegradable organic matter in wastewater. The COD should be 1.3–1.5 times the BOD for biodegradable organic materials. It is acceptable to assume that the organic matter in the wastewater is nonbiodegradable if the COD is twice the BOD value or higher.
BOD quantifies the amount of dissolved oxygen (DO) that microorganisms use to break down organic materials in an aerobic environment. Testing for BOD can take several days because it is a measurement that is based on a biological process.
Biochemical oxygen demand test procedure:
Step 1: First, make sure there is sufficient biological activity in the water sample before measuring the BOD. The following requirements for the water sample must be met in order for this to occur:
There should be no chlorine in the water. A dichlorination chemical like sodium sulphate can be used if chlorine is present in the water.
The pH range for the water sample must be between 6.5 and 7.5. An acid or a base can be introduced to the water sample to adjust the pH if it is either too high or too low.
A microbial population should be present in the water. A seed solution of bacteria and its necessary nutrient can be added to ensure the health of the microbiome if it is unknown or insufficient.
Step 2: Diluted sample water is poured into special BOD bottles (ideally 300 MLs) that are made to allow filling without any air spaces. The sample can be diluted using distilled water, and different amounts of the distilled water are used to create various dilutions in the various bottles. To serve as the control, one of the bottles should solely contain distilled water.
Step 3: Next, the amount of dissolved oxygen in each bottle is determined using a DO (Dissolved Oxygen) meter. The DO should ideally not fall below 8.) mg/L. The bottles are then each kept in an incubator for at least five days at a temperature of 20 degrees Celsius.
Step 4: Use the DO meter to gauge the final DO concentration after the five days have passed. This should have decreased to about 4.0 mg/L in the ideal situation.
Step 5: Calculate the BOD value of the water by subtracting the Initial DO from the Final DO.
COD measures the amount of DO used up during the controlled chemical oxidation of organic materials. Testing for COD will only take a few hours because it is based on a chemical process. In order to test for COD, the water sample is normally digested at 150 °C for two hours with potassium dichromate and sulfuric acid in a sealed vial.
Chemical oxygen demand test procedure:
You must first prepare a number of standards using potassium hydrogen phthalate (KHP) before finishing the COD test. It is advised to use criteria of 100, 250, 500, and 1,000 mg/L because the majority of effluent will fall into the high range.
After that, a colorimeter and a COD reactor block are both turned on so they can both reach a stable state.
In accordance with the anticipated outcomes, low-range or high-range vials are then chosen for the COD test. Both ranges can be used if the expected results are unknown.
Three to four vials are labelled with a predefined standard level, whereas one vial is designated "blank". Additionally, 2 vials are designated for use in a duplicate run of a wastewater sample. 10% of the wastewater samples must be duplicated when running multiple samples.
The appropriate vials are then filled with 2 ml of each standard. 2 ml can be added to the appropriate vial once the wastewater sample has reached its maximum strength. The 2ml dilution is added to the vial when dilution is required.
Each vial should be thoroughly mixed before being placed in a reactor block for two hours, removed, and then allowed to cool for fifteen minutes.
The results of COD and BOD tests are crucial for figuring out how much waste is present in wastewater. This is crucial because before wastewater is discharged, the organic content needs to be decreased. Rivers, lakes, and other bodies of water may become eutrophic if the organic content is not reduced. Due to the temporal differences between the BOD and COD tests, they are frequently utilized jointly. COD is utilized on a daily basis because it just takes a few hours, whereas BOD is only performed sometimes because the test takes five days to complete.
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