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NANO Barcode test BOD5-TT
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Print PageBOD5 - biochemical oxygen demand in 5 days
Besides the chemical oxygen demand (COD), the biochemical oxygen demand after 5 days (BOD5) is the most important cumulative effect parameter for the assessment of the degree of contamination of a water body.
The BOD is defined by the volume-related amount of oxygen which is consumed by microorganisms to degrade the organic matter present in the water at 20 °C by oxidation. In general, this determination is made after 5 days, why it is often referred to as the BOD5 value.
Reaction basis
The BOD content is determined by measuring the oxygen concentration. Microorganisms consume oxygen during the degradation of organic substances into carbon dioxide.
The simplified determination of the biochemical oxygen demand after 5 days (BOD5) is done with undiluted samples and without using a control in accordance with the German norm DIN EN 1899-2-H52. The oxygen-enriched, undiluted sample is incubated in a test tube for 5 days at 20 ± 1 °C in the dark. The determination of the dissolved oxygen after 5 days is based on the Winkler method. The incubation of the sample and the oxygen measurement (after 5 days) take place in the same test tube (REF 985825). In the standard method, the BOD5 is determined according to the so-called dilution principle. The oxygen concentration is measured immediately after sample preparation and after five days of incubation in Winkler bottles (REF 985 822). This method is in accordance with the German norm DIN EN 25813-G21.
Sample preservation
- Store the sample immediately after collection in a completely filled (no air bubbles!), tightly sealed bottle at a temperature of 1–5 °C in the dark until the performance of the test.
- Start the test as soon as possible, at the latest after 24 hours. Freeze the sample for longer storage.
Tips & tricks
Background information
- The test measures the oxygen consumption. A too high oxygen consumption of the dilution water leads to incorrect results. When using dilution water, measure the oxygen content of the control sample on day 0 (must be at least 8 mg/L O2) and on day 5 before starting the measurements. If the oxygen concentration difference of the control sample is greater than 2 mg/L O2, the oxygen degradation of the dilution water is too high. Possibly increase the aeration time or check for interfering ions.
- The same as described above applies when inoculating water is used instead of dilution water. The inoculating water must not have a high oxygen consumption. Again, oxygen measurements on day 0 and on day 5 before starting the analysis are recommended. The COD content of the inoculating water should be checked if the oxygen consumption is too large. The COD content should be lower than 300 mg/L O2. For higher COD concentrations, useless or if possible no inoculating water for the dilution water.
Seawater suitability
- Seawater analysis is possible.
pH
- The pH value must be between 6 and 8. pH values outside this range lead to incorrect results. If the pH is too high adjust with 0.1 N sodium hydroxide, if it is too low adjust with 0.1 N hydrochloric acid.
Interferences
- Accumulations of special microbial metabolites and substances toxic to microorganisms (e.g. mycotoxins, free chlorine, certain heavy metals) can lead to a reduction of the substrate conversion and thus to a reduction of the BOD5.
- Iron(II) salts, sulphur dioxide and hydrogen sulphide consume oxygen and also distort the BOD5 test result.
- Presence of algae or nitrifying microorganisms can lead to increased results.
- Free and/or bound chlorine has to be removed by adding a suitable amount of sodium sulphite.
