COD in wastewater

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This post was last edited by Qingfeng Xuchi on 2022-1-21 at 11:50. Chemical oxygen demand, also known as chemical oxygen consumption and abbreviated as COD, is determined by using chemical oxidants such as potassium permanganate to oxidize and decompose oxidizable substances in water, such as organic compounds, nitrites, ferrous compounds, sulfides, etc.; the amount of oxygen consumed is then calculated based on the remaining amount of the oxidant. Like biochemical oxygen demand (BOD), it is an important indicator indicating the degree of water pollution. The unit of COD is ppm or mg/L; the lower the value, the lower the degree of water pollution. In the study of river pollution and the properties of industrial wastewater, as well as in the operation and management of wastewater treatment plants, it is an important COD pollution parameter that can be measured quickly. Biological aerobic tank for milk production wastewater treatment (to reduce COD). Chemical oxygen demand (COD) is often used as an important indicator to measure the amount of organic matter in water. The higher the chemical oxygen demand, the more severe the organic pollution of the water body. The determination of Chemical Oxygen Demand (COD) varies depending on the reductive substances present in the water sample being tested, as well as the testing method used. The most commonly used determination methods at present are the acidic potassium permanganate oxidation method and the potassium dichromate oxidation method. Organic substances pose a great threat to industrial water systems. Strictly speaking, chemical oxygen demand also includes inorganic reducing substances present in water. Generally, since the amount of organic matter in wastewater is **greater than that of inorganic matter**, chemical oxygen demand is used to represent the total amount of organic matter in wastewater. Under the testing conditions, nitrogen-free organic substances in water are easily oxidized by potassium permanganate, whereas nitrogen-containing organic substances are more difficult to decompose. Therefore, oxygen consumption is suitable for measuring natural water or general wastewater containing easily oxidizable organic substances, while organic industrial wastewater with more complex compositions is often used to measure chemical oxygen demand. The impact of COD on water treatment systems: Water containing large amounts of organic matter, when passing through desalination systems, can contaminate ion exchange resins; in particular, anion exchange resins are prone to contamination, which reduces their exchange capacity. Organic matter can be reduced by about 50% during pretreatment processes such as coagulation, clarification, and filtration. However, organic matter cannot be effectively removed in desalination systems; as a result, make-up water often enters the boiler, lowering the pH of the boiler water and causing corrosion in the system ； Sometimes organic substances may also be carried into the steam system and condensate, lowering the pH value and thus causing corrosion in the system as well. Furthermore, high levels of organic matter in the circulating water system can also promote microbial growth. Therefore, for desalination, boiler water, or circulating water systems, the lower the COD, the better; however, there is currently no unified numerical standard. Note: In a circulating cooling water system, the water quality begins to deteriorate when the COD (KMnO4 method) exceeds 5 mg/L. The impact of COD in resin contaminated by organic substances on the ecosystem: A high COD level indicates the presence of large amounts of reducing substances in the water, primarily organic pollutants. The higher the COD, the more severe the organic pollution in the river water; the sources of this organic pollution are generally pesticides, chemical plants, organic fertilizers, etc. If not dealt with promptly, many organic pollutants can be adsorbed by the sediment at the bottom of rivers and settle there, causing persistent toxicity to aquatic organisms over the coming years. After a large number of aquatic organisms die, the ecosystem in the river is also gradually destroyed. If people consume such aquatic organisms, they will absorb large amounts of the toxins present in them, which then accumulate in their bodies. These toxins often have harmful effects such as causing cancer, birth defects, and mutations, and are extremely detrimental to human health. Furthermore, if polluted river water is used for irrigation, plants and crops will also be affected and grow poorly; such contaminated crops cannot be consumed by humans. However, a high chemical oxygen demand does not necessarily mean that the aforementioned hazards will occur; a final judgment can only be reached through detailed analysis. Such as analyzing the types of organic substances, and what impact they have on water quality and the ecosystem, as well as whether they are harmful to humans. If a detailed analysis is not possible, the chemical oxygen demand of the water sample can be measured again after a few days; if there is a significant decrease compared to the previous value, it indicates that the reducing substances present in the water are mainly readily degradable organic compounds, and such compounds pose relatively minor hazards to humans and organisms. Common methods for the degradation of COD wastewater currently include adsorption, chemical coagulation, electrochemical methods, ozone oxidation, biological methods, and microelectrolysis – these are the typical approaches used for reducing COD levels in wastewater. Common methods for the degradation of COD wastewater currently include adsorption, chemical coagulation, electrochemical methods, ozone oxidation, biological methods, and microelectrolysis – these are the typical approaches used for reducing COD levels in wastewater.