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How to treat water quality indicators COD, BOD, BOD5 rationally?

by:BOQU     2021-06-10


In the sewage treatment process, in order to make the treated water discharge up to the standard, the water quality monitoring equipment will be used to test the water quality in each link of the sewage treatment, and the corresponding treatment methods will be selected according to the data measured by the water quality monitoring equipment. Make the water quality target of this link meet the requirements, and then enter the next treatment link.

Among these water quality monitoring targets, the two most important and most important targets we hear are COD and BOD. So what is the difference and connection between the two?

What is COD?

COD (Chemical Oxygen Demand): It is the amount of oxidant consumed when a certain strong oxidant is used to treat water samples under certain conditions. It reflects the degree of pollution in the water. The greater the chemical oxygen demand, the more severe the pollution of organic matter in the water.

COD is indicated in mg/L. The COD value detected by water quality monitoring equipment can be divided into five categories. Among them, the first and second COD are 15mg/L, which can basically meet the drinking water standard, and the value is greater than the second category. If the water cannot be used as drinking water, the third type of COD 20mg/L, the fourth type of COD 30mg/L, and the fifth type of COD 40mg/L are classified as polluted water quality. The higher the COD value, the more severe the pollution.

What is BOD?

BOD (Biochemical Oxygen Demand): refers to the mass concentration of dissolved oxygen required in the biochemical process of microorganisms decomposing organic matter in water under aerobic conditions. In order to make the measured values u200bu200bof BOD comparable, a time period is generally specified and the dissolved oxygen consumption in the water is measured. Generally, five days are used, called the five-day biochemical oxygen demand, which is recorded as BOD5, and the five-day biochemical oxygen demand is often used. . The larger the BOD value, the more organic matter contained in the water, and therefore the more severe the pollution.

BOD is an environmental monitoring target used to monitor the pollution of organic matter in the water. Organic matter can be decomposed by microorganisms. This process requires oxygen consumption. If the dissolved oxygen in the water is not enough to supply the needs of microorganisms, the water body will deal with the pollution.

What is the relationship between COD and BOD?

In the sewage treatment process, there are hundreds of organic substances, and analyzing these organic substances one by one takes time and medicine.

Through research, it has been found that all organic substances have two things in common. One is that they are composed of hydrocarbons. The other is that most organic substances can be chemically oxidized or oxidized by microorganisms. Their carbon and hydrogen are different from oxygen. Forms non-toxic and harmless carbon dioxide and water.

The organic matter in sewage consumes oxygen both in the chemical oxidation processor in the biological oxidation process. The more organic matter in the wastewater, the more oxygen is consumed, and there is a direct ratio between the two Relationships. Therefore, the amount of oxygen consumed by the chemical oxidation of sewage is called COD (Chemical Oxygen Demand), and the amount of oxygen consumed by the oxidation of microorganisms in sewage is called BOD (Oxygen Demand).

Because COD (Chemical Oxygen Demand) and BOD (Oxygen Demand of Anger) can inductively reflect the quantity of all organic substances in the water, there are many such detection instruments, the detection method is simple, and it can be obtained in a short time. The results of testing have become an important goal of water quality monitoring and an important basis for environmental monitoring of water bodies because they have been widely used in water quality testing and analysis. We have heard more about sewage treatment.

In fact, COD (Chemical Oxygen Demand) not only reacts with organic matter in water, but it can also indicate inorganic substances with restorative properties in the water, such as sulfide, ferrous ion, sodium sulfite, etc. For example, if ferrous ions in sewage are not completely removed in the neutralization tank, there will be ferrous ions in the effluent of the biochemical treatment, and the COD (chemical oxygen demand) of the effluent may exceed the standard.

Some of the organic matter in sewage can be biologically oxidized (such as glucose and ethanol), and some can only be partially degraded by biological oxidation (such as methanol), and some organic matter cannot be degraded by biological oxidation. There is a certain degree of toxicity (some surfactants). In this way, the organic matter in the sewage can be divided into two parts, biodegradable and non-biodegradable organic matter.

Traditionally, COD (chemical oxygen demand) basically indicates all organic matter in sewage, BOD (oxygen demand of anger) is the biologically degradable organic matter in sewage, so the difference between COD and BOD can indicate the Non-biodegradable organic matter.

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