Overview

During the sewage treatment process, in order to ensure that the treated water reaches discharge standards, water quality is monitored at every step. According to the data from the water quality monitoring equipment, appropriate treatment methods are used to treat the water quality to the required range and enter the next treatment link. In the process of sewage treatment, COD and BOD are two very important indicators. So what is COD? What is BOD? What are their differences and connections?

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What is chemical oxygen demand?
Chemical oxygen demand, referred to as COD, is the amount of oxidant consumed when a strong oxidant is used to treat water samples under certain conditions. It is an indicator of the amount of reducing substances in water. Reducing substances in water include various organic substances, nitrites, sulfides, ferrous salts, etc., but the main ones are organic substances. Therefore, chemical oxygen demand is also used as an indicator to measure the amount of organic matter in water. The greater the chemical oxygen demand, the more serious the water body is polluted by organic matter.

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What is Biochemical Oxygen Demand?
Biochemical oxygen demand referred to as BOD 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 BOD detection values comparable, generally stipulate a time period, and measure the consumption of dissolved oxygen in water, generally using a five-day time, called five-day biochemical oxygen demand, recorded as BOD5, often use five-day biochemical oxygen demand. A higher BOD value indicates that the water contains more organic matter and therefore more pollution.

What is the connection between COD and BOD?
Some of the organic matter in sewage can be oxidized by biology (such as glucose and ethanol), some can only be partially degraded by biological oxidation (such as methanol), and some organic matter cannot be degraded by biological oxidation, and there are 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, and BOD (Biogen Oxygen Demand) is the biodegradable organic matter in sewage. Therefore, the difference between COD and BOD can indicate that the sewage cannot be biodegraded. of organic matter.

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How to convert the values of COD and BOD?
Strictly speaking, COD and BOD are different parameters and cannot be converted. But based on actual measurement experience, we have obtained some relationship coefficients. For example, for untreated wastewater, the coefficients of BOD5 and CODcr are between 0.35 and 0.65, and for biochemically treated wastewater, the coefficients of BOD5 and CODcr are between 0.20 and 0.35. In order to quickly display COD and BOD, the DUC2-COD Controller developed by daruifuno supports setting the coefficients of COD and BOD. Users can detect the coefficient relationship between COD and BOD5 of water quality themselves and input it into the controller, so that they can use a COD Sensor to detect the values of COD and BOD at the same time. Although this value is not particularly accurate, it is sufficient as a trend judgment.

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