1, COD: chemical oxygen demand, which refers to the amount of oxygen (mg/L) consumed by oxidizing organic matter into CO2 and H2O with an intensified chemical oxidant (potassium dichromate in China) under acidic conditions, expressed by CODcr and abbreviated as COD. The higher the chemical oxygen demand, the more organic pollutants in water, and the more serious the pollution.

2. 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, it is expressed by the five-day biochemical oxygen demand (BOD5) at 20℃.

If the composition of sewage is relatively stable, generally speaking, COD >: BOD5. Generally, BOD5/COD is greater than 0.3, which is suitable for biochemical treatment.

3. Ammonia nitrogen: refers to nitrogen in the form of free ammonia (NH3) and ammonium ion (NH4+) in water. The nitrogen content of animal organic matter is generally higher than that of plant organic matter. At the same time, the nitrogen-containing organic matter in human and animal feces is unstable and easily decomposed into ammonia. Therefore, when the content of ammonia nitrogen in water increases, it refers to the combined nitrogen in the form of ammonia or ammonium ions.

4. Total nitrogen: referred to as TN for short, it means that the nitrogen-containing compounds in sewage are divided into organic nitrogen, ammonia nitrogen, nitrite nitrogen and nitrate nitrogen, and the total amount of the four nitrogen-containing compounds is called total nitrogen (TN).

COD determination method:

1, potassium permanganate (KmnO4) method: The oxidation rate is low, but it is relatively simple, so it can be used to determine the relative comparison value of organic matter content in water samples. When COD(KmnO4 _ 4 method) is more than 5mg/L, the water quality has begun to deteriorate.

2. Potassium dichromate (K2Cr2O7) method: high oxidation rate, good reproducibility, suitable for the determination of total organic matter in water samples. ?

Extended data

Causes of sewage production:

1, industrial pollution

Industrial wastewater is the main cause of water pollution caused by industrial pollution. It accounts for most of the pollutants discharged by industry. In addition to the direct injection of industrial wastewater into the water body, solid waste and waste gas will also pollute the water body.

2. Agricultural pollution

First of all, when the surface is loose and the soil and terrain are unstable due to farming or land reclamation, it rains and a large amount of sediment flows into the water, which increases the suspended solids in the water.

Another important reason is that the use of pesticides and fertilizers is increasing day by day. Only a small amount of pesticides and fertilizers are attached or absorbed, and most of the rest remain in the soil, floating in the atmosphere, and enter and penetrate into surface water through rainfall and surface runoff, forming pollution.

3. Urban pollution

Urban pollution sources are water pollution caused by urban population concentration and urban domestic sewage, garbage and waste gas. The pollution of urban pollution sources to water bodies is mainly domestic sewage, which is a mixture of various kinds of sewage produced in people's daily life, including sewage discharged from kitchens, bathrooms and toilets.

References:

Baidu encyclopedia-ammonia nitrogen

References:

Baidu encyclopedia-sewage