Basic knowledge of sewage treatment, what do COD, BOD, and SS represent?

COD – Definition COD: Also known as Chemical Oxygen Demand (Chemical Oxygen Demand), Chemical Oxygen Demand (COD or CODcr) refers to the reduction of reducing substances in water under certain strict conditions under the action of an external strong oxidant. The amount of oxidant consumed during oxidative decomposition, expressed in mg/L of oxygen. The chemical oxygen demand reflects the degree of water pollution by reducing substances, including organic matter, nitrite, ferrous salt, sulfide, etc, but the amount of inorganic reducing substances in general water and wastewater is relatively small, and is Organic matter pollution is very common, therefore, COD can be used as a comprehensive indicator of the relative content of organic matter.

COD – Using Chemical Oxygen Demand (COD): “New Scale” for Water Quality Monitoring Citizens who are concerned about environmental protection will often hear the new term “chemical oxygen demand” (COD). The so-called COD refers to the amount of oxygen consumed by chemical oxidation of oxidizable substances in the water body. According to environmental protection experts, when the organic matter in the water is decomposed by the environment, it will consume the dissolved oxygen in the water. If the dissolved oxygen in the water is depleted, the anaerobic bacteria in the water will work, causing the water body to stink and the environment to deteriorate. Therefore, the larger the COD value, the more seriously the water body is polluted. The COD indicator is decreasing year by year, indicating that the water around us is becoming clearer and clearer.

BOD (abbreviation of Biochemical Oxygen Demand): Biochemical oxygen demand or biochemical oxygen consumption (generally refers to the five-day biochemical oxygen demand), a comprehensive indicator of the content of oxygen-demanding pollutants such as organic matter in water. Explain the total amount of dissolved oxygen in the water consumed when the organic matter in the water is oxidized and decomposed due to the biochemical action of microorganisms to make it inorganic or gasified. Usually, it means that the water sample is filled in a completely sealed dissolved oxygen bottle, cultured in the dark at 20 °C for 5 days, and the mass concentration of dissolved oxygen in the water sample before and after the incubation is measured respectively. The amount of dissolved oxygen consumed per liter of sample, expressed as BOD5. It is expressed in units of ppm or mg/L. The higher the value, the more organic pollutants in the water and the more serious the pollution. In order to make the test data comparable, a period of time is generally specified. During this period, the microorganisms are cultured with water samples at a certain temperature, and the dissolved oxygen consumption in the water is measured. Generally, a period of five days is used, which is called the five-day biochemical requirement. The amount of oxygen is recorded as BOD5. The larger the value, the more organic matter the water contains, and therefore the more serious the pollution.

BOD, Biochemical Oxygen Demand (BOD) is an environmental monitoring indicator, mainly used to monitor the pollution of organic matter in water bodies. Generally, organic matter can be decomposed by microorganisms, but when microorganisms decompose organic compounds in water, they need to consume oxygen. If the dissolved oxygen in the water is not enough to supply the needs of microorganisms, the water body is in a state of pollution. BOD is an indicator related to environmental protection.

SS: refers to the abbreviation of suspended solids in water environment research and governance. Suspended substances refer to solid substances suspended in water, including inorganic substances, organic substances, mud sand, clay, microorganisms, etc. that are insoluble in water. The content of suspended solids in water is one of the indicators to measure the degree of water pollution.

Determination method

Suspended solids in sewage (SS) detection method: Suspended solids in water (SS) refers to the solids that water samples pass through a filter membrane with a pore size of 0.45µm, are trapped on the filter membrane and are dried at 103-105℃ to a constant weight substance.

When sampling, a representative water sample of 500-1000mL is required (no protective agent can be added to prevent damage to the distribution balance between solid and liquid. Floating and submerged uneven solid substances are not suspended substances and should be removed from the water sample. ).