01
What is COD (chemical oxygen demand)?
Chemical oxygen demand (COD) refers to the amount of oxygen required for oxidized substances in wastewater to be oxidized by chemical oxidants, in milligrams of oxygen per liter.
It is currently one of the most common methods used to determine the content of organic matter in wastewater. The commonly used oxidants in COD analysis are potassium permanganate (manganese method CODMn) and potassium dichromate (chromium method CODCr), and potassium dichromate method is now commonly used.
The wastewater oxidizes organic matter under the condition of strong acid heating and boiling. When silver sulfate is used as a catalyst, the oxidation rate of most organic matter can be increased to 85-95%. If the wastewater contains a higher concentration of chloride ions, mercury sulfate should be used to shield the chloride ions to reduce interference with COD determination.
02
What is BOD5 (Biochemical Oxygen Demand)?
Biochemical oxygen demand can also characterize the degree of wastewater pollution by organic matter. The most commonly used is the 5-day biochemical oxygen demand, expressed as BOD5, which represents the amount of oxygen required for biochemical degradation of wastewater in the presence of microorganisms within 5 days. In the future, we will often use the 5-day biochemical oxygen demand.
03
What is the relationship between COD and BOD5?
Some organic matter can be degraded by biological oxidation (such as glucose and ethanol), some organic matter can only be partially degraded by biological oxidation (such as methanol), and some organic matter cannot be degraded by biological oxidation and is toxic (such as Ginkgo biloba). Phenol, ginkgolic acid, certain surfactants).
Therefore, we can divide the organic matter in the water into two parts, namely, biodegradable organic matter and non-biochemically degradable organic matter. It is generally believed that COD can basically represent all organic matter in water. BOD is a biodegradable organic matter in water, so the difference between COD and BOD can represent the non-biodegradable organic matter in wastewater.
04
What is B/C? What does B/C mean?
B/C is the abbreviation of the ratio of BOD5 to COD, which can indicate the biodegradable characteristics of wastewater. Therefore, the BOD5/COD value is often used as an evaluation index for the biodegradability of organic matter.