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Why is it so important to detect cod and bod in water quality?

by:BOQU     2021-05-19

In the sewage treatment project, in order to reach the standard discharge of the treated water, water quality monitoring equipment is used to detect the water quality of each sewage treatment stage. Based on the data measured by the water quality monitoring equipment, corresponding treatment methods are adopted. Make the water quality target of this link meet the requirements, and then proceed to the next treatment link. Among these water quality monitoring targets, the two most important targets are bod and cod.

Because the content and more types of organic wastewater contain more than ten, dozens, or even hundreds of organic matter, if some wastewater is analyzed by a qualitative and quantitative analysis, it will be time-consuming to analyze one organic matter in the wastewater. ,consumption. Can't you just use a pollution target to indicate the organic matter and its quantity in all wastewater?

Who has discovered that all organic matter environmental sciences have two things in common: they are made of at least one hydrocarbon composition; the second is that most organic materials can form non-toxic carbon dioxide with oxygen and chemically oxidize water Or the oxidation of microorganisms, carbon, and hydrogen separate them. Organic waste, whether chemical or biological oxidation in the oxidation process consumes oxygen, a variety of organic substances in wastewater, and also consumes more oxygen, which is directly proportional to the relationship between the two. Therefore, the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) used to represent the content of reducing substances in wastewater!

What are cod and bod?

Biochemical Oxygen Demand refers to the mass concentration of dissolved oxygen required by microorganisms in the biochemical process of differentiating organic matter in water under aerobic conditions. In order to make the measured value of bod comparable, a period of time is generally specified, and the consumption of dissolved oxygen in the water is measured. Generally used for five days, called five-day biochemical oxygen demand. It is recorded as bod5, and five days of biochemical oxygen demand is often used. The larger the bod value, the more organic matter contained in the water, and the more severe the pollution. Organic pollutant monitoring is an environmental monitoring target used to monitor organic pollution in water. Organic matter can be differentiated by microorganisms. Oxygen is consumed in this process. If the dissolved oxygen in the water is not enough to supply the microorganisms, the water body will deal with the pollution situation.

COD (Chemical Oxygen Demand): Under certain conditions, when a certain strong oxidant is used to treat water samples, the amount of oxidant needs to be consumed. It reflects the degree of material pollution in the water body. The greater the chemical oxygen demand, the more severe the organic pollution in the water. COD is indicated in mg/L. The COD value detected by the water quality monitor can be divided into 5 categories, among which the water quality can be divided into 5 categories. The first and second level water quality is 15 mg/L, which basically reaches the drinking water standard and is greater than the second level. The water cannot be used as drinking water. Among them, the three kinds of COD are 20 mg/L, and the four kinds of COD are 30 mg/L. The higher the COD value, the higher the COD value, the more severe the pollution.

What is the connection between BOD and COD?

Because cod (chemical oxygen demand) and bod (biochemical oxygen demand) can summarize and reflect the content of all organic substances in the water, there are many detection instruments, simple detection methods, and detection results can be obtained in a short time, so in water quality detection It has been widely used in the analysis. It has become an important goal of water quality monitoring and an important basis for water environmental monitoring and sewage treatment. We have all heard more. In fact, cod (chemical oxygen demand) not only reflects the organic matter in the water, but also represents the reducing inorganic matter in the water, such as sulfide, ferrous ion, sodium sulfite, etc., such as ferrous ion in sewage in the neutralization tank The effluent of biochemical treatment contains ferrous ions, and the COD (chemical oxygen demand) of the effluent may be overrun.

Some organic matter in sewage can be biologically oxidized (such as glucose and ethanol), some can only be partially biologically oxidized (such as methanol), and some organic matter cannot be biologically oxidized. And there is a certain degree of toxicity (some surfactants). In this way, the organic matter in sewage can be divided into two parts, namely, biodegradable and non-biodegradable organic matter. Traditionally, cod (chemical oxygen demand) basically represents all organic matter in sewage, while bod (biochemical oxygen demand) is the biodegradable organic matter in sewage. Therefore, the difference between cod and bod can represent the biodegradable organic matter in sewage. ..

What is the BOD/COD value?

We generally use the ratio of BC (BOD/COD) to indicate the biodegradability of sewage. When BOD/COD is greater than 0.3, biodegradability is generally regarded as wastewater!

Ratio link: the larger the bod5/cod value, the higher the biochemical evaluation of wastewater. Under anaerobic and anoxic conditions, anaerobic bacteria are used for the digestion and purification of organic matter in wastewater. In antibiotic wastewater, because antibiotics are a large number of bacteria and fungi, they can also digest the organic matter in the wastewater to achieve the purpose of purification. Generally, wastewater with a ratio greater than 0.3 is suitable for biological treatment. The bod5/cod index is the ratio of biochemical oxygen demand to chemical oxygen demand within 5 days, which is the target of sewage biodegradability.

The formula shows as bod5/codu003d(1-α)×(k/v):

(1) The ratio of the refractory CoDNB part of biochemical treatment to COD;

K is the final biochemical constant of BOD 5 than BODU.

It can be seen from the formula that the value of bod5/cod decreases with the increase of α, and this ratio can reflect the effect of sewage biodegradability.

When b/c; GT;0.58 is completely biodegradable;

B/Cu003d0.45-0.58, good biodegradability;

B/Cu003d0.30-0.45 biodegradable;

b/c<0.1 is not biodegradable.

BOD_5/CODu003d0.3 is generally used as the lower limit of sewage biochemical degradation.

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