The concepts of COD
, ammonia nitrogen, and total nitrogen in sewage are: 1. COD: Chemical Oxygen Demand (Chemical Oxygen Demand), which refers to the use of strong chemical oxidants (potassium dichromate legally used in China) to oxidize organic matter under acidic conditions. CO2 and consumed oxygen (mg/L), expressed in CODcr, abbreviated as COD. The higher the chemical oxygen demand, the more organic pollutants in the water and the more serious the pollution. 2. BOD: biochemical oxygen demand, the amount of oxygen required when organic pollutants in water are decomposed by aerobic microorganisms is called biochemical oxygen demand (mg/L). Generally, at 20°C, the five-day biochemical oxygen demand (BOD5) is expressed. If the sewage composition is relatively stable, generally speaking, COD>BOD5. Generally, BOD5/COD is greater than 0.3, which is considered suitable for biochemical treatment. 3. Ammonia nitrogen: refers to nitrogen existing in the form of free ammonia (NH3) and ammonium ions (NH4+) in water. The nitrogen content of animal organic matter is generally higher than that of vegetable organic matter. At the same time, nitrogen-containing organic matter in human and animal manure is very unstable and easily decomposed into ammonia. Therefore, when the content of ammonia nitrogen in water increases, it refers to the compound nitrogen existing in the form of ammonia or ammonium ions. 4. Total nitrogen: TN for short, refers to the nitrogenous compounds in sewage are divided into organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, the total of the four nitrogenous compounds is called total nitrogen (TN). COD determination method: 1. Potassium permanganate (KmnO4) method: the oxidation rate is low, but relatively simple, it can be used when determining the relative value of organic matter content in water samples. COD (KmnO4 method)>5mg/L, the water quality has begun to deteriorate. 2. Potassium dichromate method: high oxidation rate and good reproducibility, suitable for determining the total amount of organic matter in water samples. Causes of sewage: 1. Industrial pollution Industrial wastewater is the most important cause of water pollution caused by industrial pollution. It accounts for the majority of pollutants emitted by industry. In addition to the pollution caused by the direct injection of industrial waste water into the water body, solid waste and exhaust gas will also pollute the water body. 2. Agricultural pollution is firstly due to plowing or land reclamation to loosen the land surface. When the soil and terrain are not stable, it rains, and a large amount of sediment flows into the water, increasing the suspended solids in the water. Another important reason is that the use of pesticides and chemical fertilizers is increasing day by day, and only a small amount of pesticides and chemical fertilizers used are attached or absorbed, and most of the rest remain in the soil and float in the atmosphere, and enter through rainfall and surface runoff. Contamination of surface water and infiltration into surface water. 3. Urban pollution Urban pollution sources are caused by the concentration of urban population, urban domestic sewage, garbage and waste gas causing water pollution. The pollution of water bodies by urban pollution sources is mainly domestic sewage, which is a mixture of various sewage produced in people's daily life, including sewage discharged from kitchens, laundry rooms, bathrooms and toilets.
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