Relationships among several indicators indicating the organic content in wastewater (discussion concluded, answers included)
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As we all know, TOC, TOD, COD, and BOD can all indicate the level of organic matter in wastewater. So let’s discuss what the quantitative relationship is among these four values Please provide a simple analysis and give the answer. Some people think there is no quantitative relationship; what do you think? We welcome everyone to share their insights, discuss together, and make progress together! Addition: Of course, the view that there is no quantitative relationship makes sense, but from the perspective of indicating the amount of organic matter in wastewater, it should be possible to make comparisons. Correct answer: TOD>TOC>COD>BOD. For details, see page 4. Last edited by Fightinghard on 2009-4-20 at 14:23.]
COD = TOC + amount of oxygen consumed by reducible inorganic substances in water. BOD5/COD = coefficient (this coefficient varies depending on the type of water; it is generally less than 1, with values typically ranging from 0.3 to 0.6). TOD refers to the total oxygen demand, which denotes the amount of oxygen required to oxidize the substances present in water, mainly organic substances, into stable oxides; the result is expressed in mg/L of O2. BOD5/TOD = 0.1-0.6 ； COD/TOD = 0.5–0.9, with the specific ratio depending on the characteristics of the wastewater. The ratio of TOD to TOC can be used to roughly determine the type of organic matter. For carbon-containing compounds, since one carbon atom consumes two oxygen atoms, that is O2/C = 2.67, theoretically TOD = 2.67 TOC. If the TOD/TOC ratio of a water sample is around 2.67, it can be considered that it mainly contains carbon-based organic matter ； If TOD/TOC > 4.0, the presence of a large amount of sulfur- and phosphorus-containing organic matter in the water should be considered ； If TOD/TOC < 2.6, it should be considered that the nitrate and nitrite contents in the water sample may be high; these substances release oxygen under high-temperature and catalytic conditions, resulting in a negative error in the TOD measurement.
The numerical relationship among the various oxygen consumption parameters is TOD > CODcr > BOD5.
This is a problem I encountered a couple of days ago. At that time, the correct order was not determined either. Upon reviewing relevant materials, it can be concluded that the correct order should be: TOD > TOC > COD > BOD. References: “BOD_5_COD and TOC_TOD” and “BOD_5_COD and TOC_TOD (continued)”