In the sewage treatment process, in order to achieve the discharge of the treated water, the water quality monitoring equipment will be used to detect the water quality in each link of the sewage treatment. According to the data measured by the water quality monitoring equipment, the corresponding treatment method is adopted to make this link The water quality index meets the requirements, and then enters the next treatment link. Among these water quality monitoring indicators, the two most-heard and most important indicators are COD and BOD. So what is the difference and connection between these two? Zero distance introduces to you why COD and BOD are commonly used in water pollution indicators, and the difference and connection between COD and BOD.
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 serious the pollution of organic matter in the water. COD is expressed in mg/L. The value of COD detected by water quality monitoring equipment can be divided into five categories. Among them, the first and second types of COD are less than or equal to 15 mg/L, which can basically meet the drinking water standard, and the value is greater than the second type of water. Those that cannot be used as drinking water, among which three types of COD≤20mg/L, four types of COD≤30mg/L, and five types of COD≤40mg/L belong to polluted water quality. The higher the COD value, the more serious the pollution.
What Is BOD ?
BOD (Biochemical Oxygen Demand): refers to the mass concentration of dissolved oxygen required in the biochemical process of microorganisms in water to decompose organic matter under aerobic conditions. In order to make the measured values of 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 serious the pollution.
BOD is an environmental monitoring indicator used to monitor the pollution of organic matter in water. Organic matter can be decomposed by microorganisms. Oxygen is consumed in this process. If the dissolved oxygen in the water is not enough to supply the needs of microorganisms, the water body will deal with the pollution state.
BOD is an environmental monitoring indicator used to monitor the pollution of organic matter in water. Organic matter can be decomposed by microorganisms. Oxygen is consumed in this process. If the dissolved oxygen in the water is not enough to supply the needs of microorganisms, the water body will deal with the pollution state.
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. After research, it is found that all organic substances have two things in common. One is that they are all composed of hydrocarbons. The other is that most organic substances can be chemically oxidized or oxidized by microorganisms. Their carbon and hydrogen form non-toxic with oxygen. Harmless carbon dioxide and water. The organic matter in sewage consumes oxygen both in the chemical oxidation process or in the biological oxidation process. The more organic matter in the wastewater, the more oxygen is consumed. There is a direct proportional relationship between the two. Therefore, the amount of oxygen consumed by 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 for Gas).
Since COD (Chemical Oxygen Demand) and BOD (Oxygen Demand for Gas) can comprehensively reflect the quantity of all organic substances in the water, there are also many such detection instruments, the detection method is simple, and the detection results can be obtained in a short time. Therefore, it is widely used in water quality detection and analysis, and it has become an important indicator of water quality monitoring and an important basis for environmental monitoring of water bodies. We have heard comparisons in sewage treatment.
In fact, COD (Chemical Oxygen Demand) not only reacts with organic substances in water, but also represents inorganic substances with reducing properties in water, such as sulfides, ferrous ions, and sodium sulfite. For example, if the ferrous ions in the 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, and some Toxicity (certain 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 means all the organic matter in sewage, BOD (oxygen demand for gasification) is the organic matter that can be biodegraded in sewage, so the difference between COD and BOD can indicate that the sewage cannot be biodegradable Of organic matter.