The relationship between COD and BOD

Speaking of COD and BOD
In professional terms
COD stands for Chemical Oxygen Demand. Chemical Oxygen Demand is an important water quality pollution indicator, used to indicate the amount of reducing substances (mainly organic matter) in the water. The measurement of COD is calculated by using strong oxidants (such as potassium dichromate or potassium permanganate) to treat water samples under certain conditions, and the amount of oxidants consumed can roughly indicate the degree of organic matter pollution in water bodies. The larger the COD value, the more serious the water body is polluted by organic matter.
The measurement methods of chemical oxygen demand mainly include dichromate method, potassium permanganate method and newer ultraviolet absorption method. Among them, the potassium dichromate method has high measurement results and is suitable for occasions with high accuracy requirements, such as industrial wastewater monitoring; while the potassium permanganate method is easy to operate, economical and practical, and is suitable for surface water, water sources and drinking water. Water monitoring.
The reasons for excessive chemical oxygen demand are usually related to industrial emissions, urban sewage and agricultural activities. Organic matter and reducing substances from these sources enter the water body, causing COD values to exceed the standard. In order to control excessive COD, effective measures need to be taken to reduce emissions from these pollution sources and strengthen water pollution control.
To sum up, chemical oxygen demand is an important indicator that reflects the degree of organic pollution of water bodies. By using different measurement methods, we can understand the pollution of water bodies and then take corresponding measures for treatment.
BOD stands for Biochemical Oxygen Demand. Biochemical oxygen demand (BOD5) is a comprehensive indicator indicating the content of oxygen-demanding substances such as organic compounds in water. When organic matter contained in water comes into contact with air, it is decomposed by aerobic microorganisms and becomes inorganic or gasified. The measurement of biochemical oxygen demand is usually based on the reduction of oxygen in the water after a reaction at a certain temperature (20°C) for a specified number of days (usually 5 days).
Reasons for high biochemical oxygen demand may include high levels of organic matter in the water, which are decomposed by microorganisms and consume large amounts of oxygen. For example, industrial, agricultural, aquatic water, etc. require that the biochemical oxygen demand should be less than 5mg/L, while drinking water should be less than 1mg/L.
Biochemical oxygen demand determination methods include dilution and inoculation methods, in which the reduction in dissolved oxygen after the diluted water sample is incubated in a constant temperature incubator at 20°C for 5 days is used to calculate BOD. In addition, the ratio of biochemical oxygen demand to chemical oxygen demand (COD) can indicate how many organic pollutants in the water are difficult for microorganisms to decompose. These organic pollutants that are difficult to decompose cause greater harm to the environment.
Biochemical oxygen demand load (BOD load) is also used to indicate the amount of organic matter processed per unit volume of wastewater treatment facilities (such as biological filters, aeration tanks, etc.). It is used to determine the volume of wastewater treatment facilities and the operation and management of the facilities. important factors.
COD and BOD have a common feature, that is, they can be used as a comprehensive indicator to reflect the content of organic pollutants in water. Their attitudes towards the oxidation of organic matter are completely different.
COD: Bold and unrestrained style, generally uses potassium permanganate or potassium dichromate as the oxidant, supplemented by high-temperature digestion. It pays attention to a fast, accurate and ruthless method, and oxidizes all organic matter in a short time through spectrophotometry, dichromate The amount of oxygen consumed is counted by detection methods such as the method, which are recorded as CODcr and CODmn according to different oxidants. Normally, potassium dichromate is generally used to measure sewage. The COD value that is often mentioned is actually the CODcr value, and potassium permanganate is The value measured for drinking water and surface water is called the permanganate index, which is also the CODmn value. No matter which oxidant is used to measure COD, the higher the COD value, the more serious the pollution of the water body.
BOD: Gentle type. Under specific conditions, microorganisms are relied on to decompose biodegradable organic matter in water to calculate the amount of dissolved oxygen consumed in the biochemical reaction. Pay attention to a step-by-step process. For example, if the time for biological oxidation is 5 days, it is recorded as five days of biochemical reactions. Oxygen demand (BOD5), correspondingly BOD10, BOD30, BOD reflects the amount of biodegradable organic matter in the water. Compared with the violent oxidation of COD, it is difficult for microorganisms to oxidize some organic matter, so the BOD value can be regarded as sewage The concentration of organic matter that can be biodegraded
, which has important reference significance for sewage treatment, river self-purification, etc.

COD and BOD are both indicators of the concentration of organic pollutants in water. According to the ratio of BOD5/COD, the indicator of biodegradability of sewage can be obtained:
The formula is: BOD5/COD=(1-α)×(K/V)
When B/C＞0.58, completely biodegradable
B/C=0.45-0.58 good biodegradability
B/C=0.30-0.45 Biodegradable
0.1 B/C＜0.1 Not biodegradable
BOD5/COD=0.3 is usually set as the lower limit of biodegradable sewage.
Lianhua can quickly analyze the results of COD in water within 20 minutes, and can also provide various reagents, such as powder reagents, liquid reagents and pre-made reagents. The operation is safe and simple, the results are quick and accurate, the reagent consumption is small, and the pollution is small.
Lianhua can also provide various BOD detection instruments, such as instruments that use the biofilm method to quickly measure BOD in 8 minutes, and BOD5, BOD7 and BOD30 that use the mercury-free differential pressure method, which are suitable for various detection scenarios.