The theoretical oxygen demand

If the composition of the waste stream is known, then the theoretical oxygen demand can be calculated from the appropriate stoichiometric equations. As a first level of approximation, we can assume that this theoretical oxygen demand would be equal to the COD. Then, experience with domestic sewage indicates that the average ratio of COD to BOD will be on the order 1.5 to 2. The following example will help to clarify these relationships. 

Solution First, calculate the theoretical oxygen demand from the equation that represents the overall oxidation of the acetone ... 

Also the traditional BOD5 tests (e.g. the EU C.5 test) may demonstrate whether a substance is readily biodegradable. In this test, the relative biochemical oxygen demand in a period of 5 days is compared to the theoretical oxygen demand (ThOD) or, when this is not available, the chemical oxygen demand (COD). The test is completed within five days and consequently, the pass level defined in the proposed hazard classification criteria at 50% is lower than in the ready biodegradability tests. 

What would be the theoretical oxygen demand of a wastewater stream from an integrated steel mill which contains ... 

Theoretical oxygen demand, ThOD The theoretical oxygen demand is the amount of oxygen required to completely oxidise a given chemical compound, calculated from its chemical formula. 

The theoretical oxygen demand (ThOD), is solely the oxygen needed on a stochiometric basis to oxidize the solvent completely, and is thus the worst possible effect, but may be useful if no laboratory results are available. In this book the values of ThOD do not include for the oxidation of the nitrogen where it exists in the solvent s molecule. This tends to be a slow reaction and seldom is represented in the five-day BOD test. 

The level of biodegradation, expressed in per cent, is determined by comparing the BOD with the theoretical oxygen demand (ThOD) or by comparing the amount of carbon dioxide evolved with the theoretical amoimt (ThC02). The influence of possible nitrification processes on the BOD has to be considered. The test is terminated when a constant level of biodegradation has been attained or, at the latest, after six months. 

C5, C7, C8 biochemical oxygen demand (BOD). Degradation is defined as the ratio between the BOD and the theoretical oxygen demand (ThOD) ... 

In addition to these measurements the Theoretical Oxygen Demand (THOD) is also often calculated. This is done by calculating the amount of oxygen required to convert all organic substances to carbon dioxide and water. Additionally, oxidation of certain inorganic species to nitrate, sulfate... 

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