What does cod mean

What does COD mean: Chemical oxygen demand (COD) is a chemical method to detect the amount of reducing substances that need to be oxidized in a water sample
.

Oxygen value of substances that can be oxidized by strong oxidants in sewage, wastewater treatment plant effluent and contaminated water
.

Chemical oxygen demand (COD) is the amount of oxidant consumed when a water sample is treated with a corresponding strong oxidant under corresponding conditions
.

It is an index value indicating the amount of reducing substances in water
.

The reducing substances in water include various organic substances, nitrites, sulfides, ferrous salts, etc.
, but the main ones are organic substances
.

Therefore, chemical oxygen demand (COD) is often used as an index value to measure the amount of organic matter in water
.

The greater the chemical oxygen demand, the more serious the water pollution by organic matter
.

 The methods of measuring COD are: ① spectrophotometry, ② sealed digestion method, ③ electrochemical method, ④ determination of high chloride wastewater, ⑤ rapid meter spectrophotometry: spectrophotometry is very important in water quality because of its simplicity, speed and accuracy.
It is widely used in monitoring, and in recent years, many applied studies on the rapid determination of spectrophotometry have been reported
.

Research shows that this method has the advantages of fast test speed, less sampling, convenient operation and low cost
.

The measurement principle is that in an acidic solution, the reducing substance in the test solution reacts with potassium dichromate to generate trivalent chromium ions.
The correlation of the concentration obeys the Lambert-Beer law, and the trivalent chromium ion is related to the amount of reducing substances in the test solution
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Therefore, the value of the test solution can be indirectly measured by measuring the absorbance of trivalent chromium
.

 　　Speed ​​tester: In recent years, various types of speed testers have been successfully developed and put into the industry market, and have been used in many monitoring stations and laboratories
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It can be applied to various waste water online monitoring, suitable for various environments, outdoor online base station is equipped with constant temperature system and thermal insulation material, and can measure the value of one sample per hour
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 　　Sealing digestion method: The microwave sealing rapid method is the same as the national standard reflux method, using a potassium sulfate-dichromate digestion system
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Under the catalysis of silver sulfate, high-energy electromagnetic waves are used to heat the reaction solution
.

Under the action of high-frequency microwave, the molecules of the reaction solution produce high-speed frictional motion, which makes the temperature rise rapidly, and the sealed digestion method is adopted to rapidly increase the internal pressure of the digestion tank, and achieve the purpose of rapid digestion under high temperature and high pressure
.

The excess potassium dichromate after digestion is tested with ferrous spirit as an indicator, and the value is calculated by back-dropping the standard solution and according to the consumption of money
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The advantages of the method are that the amount of reagents is small, fast and simple, no special equipment is required, and the sample is digested in a constant temperature oven, which can be carried out even in a very simple laboratory, and is easy to popularize
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 The national COD emission industry standards are: Allowable emission concentration of basic control items (daily average value) Unit mg/L Serial number Basic control items Level 1 Standard Level 2 Standard Level 3 Standard A Standard B Standard 1 Chemical Oxygen Demand (COD) 50 60 100 120① 2 Biochemical oxygen demand (BOD5) 10 20 30 60① 3 Suspended solids (SS) 10 20 30 50 4 Animal and vegetable oils 1 3 5 20 5 Petroleum 1 3 5 15 6 Anionic surfactants 0.
5 1 2 5 7 Total nitrogen (calculated as N) 15 20 - - 8 Ammonia nitrogen (calculated as N)② 5(8) 8(15) 25(30) - 9 Total phosphorus Constructed before December 31, 2005 1 1.
5 3 5 (in terms of P) 0.
000 for construction since January 1, 20065 1 3 5 10 Chromaticity (dilution factor) 30 30 40 50 11 pH June 9th 12 Fecal coliform count (unit/L) 103 104 104 - "Water Pollutant Discharge Standard for Pulp and Paper Industry" (GB 3544 -2008) The wastewater discharge of waste paper pulping enterprises shall be implemented according to the standard of bleached wood pulp and uncolored wood pulp with and without deinking process respectively.

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　　The wastewater discharge of chemical-mechanical pulping enterprises shall comply with the standards of bleached wood pulp and unbleached wood pulp respectively according to the process with and without bleaching
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　　The standard of chemical oxygen demand for pure pulping or pulp-paper production balance production is relatively high, 400 mg/l for bleached pulp and 350 mg/l for non-bleached pulp
.

　　The bleached non-wood pulp is 450mg/l, and the non-wood pulp is 400mg/l
.

　　The lower standard of chemical oxygen demand in paper production is 100 mg/l for pure paper production or paper production with paper production greater than pulp production
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"Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry" (GB 4287-2012) This standard stipulates different discharge standards for chemical oxygen demand according to the different years of project establishment and operation of textile dyeing and finishing industry construction projects
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　　The textile dyeing and finishing industry construction project established on July 1, 1992 and the enterprises put into production after completion have a first-level standard of 100mg/l, a second-level standard of 180mg/l, and a third-level standard of 500mg/l
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"Water Pollutant Discharge Standard for Meat Processing Industry" (GB13457-92) Processing categories are divided into: livestock slaughtering and processing; meat product processing; poultry slaughtering and processing
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　　According to the different types of discharge into the waters, the first, second and third standards are implemented respectively
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　　The first, second and third level standards implemented by the construction projects established before January 1, 1989 and the enterprises put into production after completion are 120mg/l, 160mg/l and 500mg/l respectively
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　　The first-, second-, and third-level standards for construction projects established from January 1, 1989 to June 30, 1992 and enterprises put into production after completion are 100mg/l, 120mg/l, and 500mg/l, respectively
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　　The first-, second-, and third-level standards for the construction projects initiated on July 1, 1992 and for poultry slaughtering and processing enterprises after completion are 70mg/l, 100mg/l, and 500mg/l, respectively, and the first and second-level standards for livestock slaughtering and processing enterprises , the three-level standards are 80mg/l, 120mg/l, 500mg/l respectively
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　　If you want to know about COD analyzer, ammonia nitrogen analyzer, total phosphorus analyzer, total nitrogen analyzer, multi-parameter water quality analyzer, digestion apparatus and other water quality equipment
.

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