How to rationally view the water quality indicators COD
How to rationally view the water quality indicators COD
In the process of sewage treatment, 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 will be adopted to make this link The water quality index meets the requirements, and then enter the next treatment link.
'Among these water quality monitoring indicators, the two most commonly heard indicators are COD and BOD. So what is the difference and connection between these two?
What is COD?
COD (Chemical Oxygen Demand): It is the amount of oxidant consumed when a certain strong oxidant is used to treat a water sample under certain conditions. It reflects the degree of pollution of substances in water. The greater the chemical oxygen demand, the more serious the pollution of organic matter in water.
COD is expressed in mg/L. The COD value detected by the water quality monitoring instrument can be divided into five categories, of which the first and second categories have a COD ≤15mg/L, which basically meets the drinking water standard, and the value is greater than the second category of water. Can not 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 microbial decomposition of organic matter in water under aerobic conditions. In order to make the BOD detection values ??comparable, a time period is generally specified and the consumption of dissolved oxygen in the water is measured. It is generally used for five days, which is called the five-day biochemical oxygen demand, which is recorded as BOD5, and the five-day biochemical oxygen demand is often used . The larger BOD value proves that the water contains more organic matter, so the pollution is more serious.
BOD is an environmental monitoring indicator used to monitor the pollution of organic matter in 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 status.
What is the relationship between COD and BOD?
In the process of sewage treatment, there are hundreds of organic substances. Analyzing these organic substances one by one will consume both time and medicine.
'After research, it is found that all organic substances have two common characteristics. First, they are composed of hydrocarbons. Second, most organic substances can be chemically oxidized or oxidized by microorganisms. Their carbon and hydrogen form no oxygen with oxygen, respectively. Poisonous and harmless carbon dioxide and water.
The organic matter in the sewage consumes oxygen no matter in the chemical oxidation process or the biological oxidation process. The more organic matter in the waste water, the more oxygen is consumed, and there is a positive 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 microorganisms in sewage is called BOD (oxygen demand).
Because COD (chemical oxygen demand) and BOD (gas generation oxygen demand) can comprehensively reflect the amount of all organic matter in the water, there are more such detection instruments, the detection method is simple, and the detection result can be obtained in a short time. Therefore, it is widely used in water quality detection and analysis, becoming an important indicator of water quality monitoring and an important basis for environmental monitoring of water bodies. We have heard more about sewage treatment.
In fact, COD (Chemical Oxygen Demand) not only reacts with organic matter in water, but also represents inorganic substances with reducing properties in water, such as sulfide, ferrous ion, sodium sulfite, etc. For example, if the ferrous ions in the sewage are not completely removed in the neutralization tank, there is ferrous ions in the biochemical treatment effluent, and the effluent COD (chemical oxygen demand) may exceed the standard.
Some organic substances in sewage can be biooxidized (such as glucose and ethanol), some can only be partially degraded by biooxidation (such as methanol), and some organic matter cannot be degraded by biooxidation, and there are still certain 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 represents all organic matter in sewage, BOD (Body Oxygen Demand) is biodegradable organic matter in sewage, so the difference between COD and BOD can indicate that the sewage cannot be biodegraded Organic matter.
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