![]() In contrast to the dilution BOD, it is necessary to continuously stir the samples during the incubation at 20 ☌. From this, the measuring head directly calculates the BOD and, if desired, even shows the curve over the incubation period on the display. The carbon dioxide resulting from the biodegradation process forms a solid precipitate of sodium carbonate with the sodium hydroxide, which causes a pressure drop. A rubber quiver in the measuring bottle contains sodium hydroxide, on which an electronic pressure measuring head is screwed. The much more frequently used method for BOD measurement as part of the self-monitoring procedure is pressure measurement in a closed bottle with undiluted samples according to DIN EN 1899-2, for instance with the OxiTop®-i. Different sample volumes are used here, depending on the measuring range, which are simply filled with special volumetric flasks. Self-stirring BOD oxygen sensor StirrOx® G in a Karlsruhe bottle The disadvantage of this method is that it is somewhat complicated to carry out and requires trained and experienced laboratory personnel. In the case of municipal wastewater, it is approximately half or up to two thirds of the COD. according to DIN EN 1899-1, where the waste water to be analyzed is prepared in dilution series with a nutrient containing dilution water according to its expected range and the dissolved oxygen is determined by measuring with an oxygen sensor in the samples before and after their five day incubation at 20 ☌. There are two common procedures for the BOD: The worldwide accepted reporting method is the dilution BOD, e.g. The Biochemical Oxygen Demand (BOD) is part of the COD, but in contrast to the COD it contains the biodegradable portion, caused by the respiration of the dissolved carbon load by microorganisms. DIN 38409-41 describes the procedure for its determination. Chemical oxygen demand (COD) is a sum parameter that includes all dissolved or particulate substances in wastewater and determines the oxygen required for their oxidation, provided that oxygen is the oxidizing agent.
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