Why must samples containing caustic alkalinity or acidity be adjusted before preparing BOD dilutions?
Caustic alkalinity or acidity can prevent bacteria from growing during the course of the BOD test. To prevent this, samples which have pH values higher than pH 8.0 or lower than pH 6.0 must be neutralized to pH 7.0 before the test is performed.
How is biochemical oxygen demand measured?
Measuring biochemical oxygen demand requires taking two measurements. One is measured immediately for dissolved oxygen (initial), and the second is incubated in the lab for 5 days and then tested for the amount of dissolved oxygen remaining (final).
What is the standard method for BOD determination?
5-Day BOD Test The method consists of filling with sample, to overflowing, an airtight bottle of the specified size and incubating it at the specified temperature for 5 d. Dissolved oxygen is measured initially and after incubation, and the BOD is computed from the difference between initial and final DO.
Why Koh is used in BOD test?
This measurement is performed in an incubated system. The microorganisms contained in wastewater samples consume oxygen and produce carbon dioxide. Potassium hydroxide (KOH) that absorbs this carbon dioxide is ad- ded in the container above the sample.
Why do you dilute the sample with the dilution water and not with the distilled or tap water?
since the saturation of DO in water is limited. in ideal condition (distilled water and 0 oC) it can not be solved more than 14.6 mg/L. So for natural waters it decrease to below 10 mg/L. As you can not have more than this values , the waste-water should be diluted.
How do you determine COD?
The most common test method is the colorimetric analysis after oxidizing the COD with acid and using indicator compounds, such as hexavalent dichromate. In some instances, however, there are compounds that will interfere with the colorimetric analysis, and titration is required to determine COD levels.
How does Winkler method work?
A sample bottle is filled completely with water (no air is left to skew the results). The dissolved oxygen in the sample is then “fixed” by adding a series of reagents that form an acid compound that is then titrated with a neutralizing compound that results in a color change.
What is Winkler’s reagent?
The Winkler Method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water body, where higher dissolved oxygen concentrations are correlated with high productivity and little pollution.
Why phosphate buffer is used in BOD?
Phosphate buffer is a key reagent because phosphorus is the limiting nutrient in stimulating growth, so it must be added the day the water is used.
What’s the difference between distilled and deionized water?
Deionized (DI) water is water that has been treated to remove all ions – typically, that means all of the dissolved mineral salts. Distilled water has been boiled so that it evaporates and then re-condensed, leaving most impurities behind.
What are the limitations of BOD test?
Limitations Of Test The method takes five days to perform and uses a discrete sample. The test has poor reproducibility and toxic chemicals can inhibit measurement. Short-term BOD determinations magnify errors and still require relatively long sample periods. The test is not suited for on-line, continuous measurement.
Why sulphuric acid is used in COD?
Chemical Oxygen Demand (COD) 1% Silver Sulphate in Sulphuric Acid (conc.) provides the primary and secondary digestion catalysts for oxidation of carbon during chemical oxidation.
Which titrant is used for determination of COD?
ferrous ammonium sulfate
In the titration method for determining COD, the excess dichromate is reacted with a reducing agent, ferrous ammonium sulfate. As the ferrous ammonium sulfate (FAS) is added slowly, the excess dichromate is converted into its trivalent form.
What is biochemical oxygen demand testing?
General Discussion Biochemical oxygen demand (BOD) testing determines the relative oxygen requirements of wastewaters, effluents, and polluted waters. Its widest application is in measuring waste loadings to treatment plants and in evaluating a plant’s efficiency in removing BOD.
How do you determine alkalinity from titration results?
Gran alkalinity can also be determined simultaneously. Alkalinity analysis involves the titration of samples with standard 0.02N sulphuric acid (H 2 SO 4) titrant to endpoints of pH 8.3 and 4.5.
What is the method of alkalinity analysis?
Method Summary. Alkalinity analysis involves the titration of samples with standard 0.02N sulphuric acid (H 2SO 4) titrant to endpoints of pH 8.3 and 4.5. For alkalinities less than 20 mg CaCO 3/L, an additional endpoint at pH 4.2 is recorded.
How is dissolved oxygen fixed in titration?
The dissolved oxygen is then “fixed” using a series of reagents that form an acid compound that is titrated. Titration involves the drop-by-drop addition of a reagent that neutralizes the acid compound and causes a change in the color of the solution.