in Water Quality Monitoring

Chemical Oxygen Demand-(COD) Sensor Definition & Measurement Method

As an important means to prevent and control sewage, water quality monitoring has been paid more and more attention by the national environmental protection department.

Chemical Oxygen Demand-(COD) is one of the most important indicators. Chemical oxygen demand directly reflects the extent of water resources being destroyed by reducing pollutants.

If the median value of water is high, the pollutants will consume more dissolved oxygen in the water, resulting in water anoxia, resulting in the death of a large number of organisms due to anoxia.

At the same time, causing a large number of anaerobic bacteria in the water, accelerating the deterioration of water quality.

COD Definition

After the organic pollutants in the water sample are oxidized and digested, water and inorganic salts are generated. It is necessary to use detection technology to determine and analyze Chemical Oxygen Demand (COD) in the water sample.

What is Chemical Oxygen Demand – COD?

COD (Chemical Oxygen Demand): refers to the oxidation dose consumed when a certain strong oxidant is used to treat water samples under certain conditions. It reflects the degree of material pollution in the water. The greater the chemical oxygen demand is, the more serious the organic pollution is.

The COD detection unit is expressed in mg/L. the water quality can be divided into five categories according to the COD value detected by the water quality monitoring instrument.

COD of class 1 and class 2 ≤ 15mg / L, basically meeting the drinking water standard,

Water with a value greater than class 2 cannot be used as drinking water,

Among them, class 3 of COD ≤ 20mg / L，class 4 of COD ≤ 30mg / L and class 5 of COD ≤ 40mg / L belong to polluted water quality.

The higher the COD value, the more serious the pollution.

CHAPTER 2:

Chemical Oxygen Demand (COD) Measurement Method

In this paper, the international general testing standards and some new testing methods are introduced one by one.

Such as spectrophotometry, coulometry and electrochemistry.

National standard method detection
To detect the content of organic pollutants in the water sample, first add strong oxidant to the water sample, then carry out oxidation digestion by heating reflux, and finally use chemical reagent titration to calculate the chemical oxygen demand of the water sample by measuring the chemical reagent consumed.
(1) Dichromate reflux method
Determination principle: in sulfuric acid medium, potassium dichromate is used as oxidant, silver sulfate as catalyst, mercury sulfate as masking agent of chloride ion, sulfuric acid acidity of digestion reaction liquid is 9mol / L, heating makes digestion reaction liquid boil, boiling point temperature of 148 ℃± 2 ℃ is digestion temperature.
The reaction was heated by water cooling and refluxing for 2 h. After the digestion solution cooled naturally, the residual potassium dichromate was titrated with ammonium ferrous sulfate solution, and the COD value of the water sample was calculated according to the consumption of ferrous sulfate solution.
(2) Potassium permanganate method
Determination principle: potassium permanganate is used as oxidant to determine COD. The COD measured is called permanganate index (CODMn).
After sulfuric acid is added to the water sample, a certain amount of potassium permanganate solution is added, and the reaction is heated in a boiling water bath for 30 minutes.
The residual potassium permanganate is reduced by adding excess sodium oxalate solution, and then the excess sodium oxalate is dropped back by potassium permanganate solution, and the permanganate index is calculated.
Spectrophotometry
UV spectrophotometry is a qualitative or quantitative analysis method based on the different absorption capacity of different substances.
In acid solution, the reductive substance in the test solution reacts with potassium dichromate to form trivalent chromium ion. Trivalent chromium ion has great absorption capacity for light with wavelength of 600nm. The relationship between the absorbance and trivalent chromium ion concentration obeys Lambert Beer law.
Trivalent chromium ion is related to the amount of reducing substances in the test solution, so the COD value of the test solution can be indirectly measured by measuring the absorbance of trivalent chromium.
Electrochemical method
Electrochemical method is a new detection method developed rapidly in recent years. It is based on the integration of electrochemistry and electronic power technology.
Through the electrochemical reaction between the electrode and the water sample solution to be measured, the chemical composition of the medium is analyzed
This method has the advantages of fast reaction speed, low time consumption, simple operation, high accuracy and no secondary pollution.
Atomic absorption method
Atomic absorption method is a new detection method improved on the basis of national standard method. Its detection principle is that in acid medium, K2Cr2O7 is used to oxidize and digest the water sample to be measured. After the reaction is completed, Cr3 + or excessive Cr6 + extracted by the extractant is used to determine Cr6 + in organic phase or Cr3 + in water phase, so as to obtain the chemical oxygen demand of water sample.

CHAPTER 3:

Pros & Cons

This chapter introduces the advantages and disadvantages of each detection method.

	Advantages	Disadvantages
Dichromate Reflux Method	Universal international standard High precision	Takes up a large amount of experimental space, The consumption of water and electricity is large, Large amount of reagent, Inconvenient operation, Difficult to measure in large quantities.
Potassium Permanganate Method	Universal international standard High precision	Takes a long time to drip back excessive sodium oxalate. Acid potassium permanganate method has low oxidizability and incomplete oxidization. Permanganate index is 3-8 times lower than the chromate index.
Spectrophotometry	The detection time is saved, No titration is needed, The operation is convenient.	Low accuracy, qualitative or trend analysis
Electrochemical Method	Fast reaction speed and less time consuming, The process is simple and easy to operate, The measurement results are accurate, No secondary pollution,	The electrode has short service life. The reproducibility is not high.
Atomic Absorption Method	High sensitivity, Small sample demand, The measured value is more accurate.	A lot of organic extractants are needed, Secondary pollution to the environment, The reaction time is long.

CHAPTER 4:

Applications

COD monitoring can be seen in each water quality project. They can be found in every corner of our lives and play a huge role.

Water quality inspection of rivers and lakes
Industrial and mining enterprises, detection of urban sewage discharge
Water quality monitoring of petrochemical, chemical, power generation, pharmaceutical, food, electronic, water plant, etc
Water quality inspection of urban parks
Smart city water quality detection

CHAPTER 5:

Find More About Chemical Oxygen Demand (COD)

COD Water Quality Monitoring is already a trend in our current life. I hope the audience can learn more from other aspects. Including Wikimedia/Patent/Video and so on.

WikiPedia

Chemical Oxygen Demand
In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (mg/L). A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD).
ISO 6060:1989 Water quality — Determination of the chemical oxygen demand
Abstract
Method specified is applicable to water with a value between 30 mg/l and 700 mg/l. The chloride contents must not exceed 1 000 mg/l. If the value exceeds 700 mg/l, the water sample is diluted. For greatest accuracy it is preferable that the value of the sample is in the range of 300 mg/l to 600 mg/l.

Patents

WO2020007611A1:Method of determining chemical oxygen demand (cod) for high chloride samples
The present invention provides a method of determining chemical oxygen demand (COD) for a sample with a high concentration of chloride. The method includes obtaining the sample, determining a concentration of chloride in the sample to obtain a known concentration of chloride in the sample, dosing an amount of the sample, an acid and an oxidizing agent into a container to obtain an analyte, heating the container containing the analyte, photometrically determining a preliminary chemical oxygen demand (COD) of the analyte in an analytic device, and correcting for the high concentration of chloride using a chloride correction to obtain the chemical oxygen demand (COD).
Other languagesFrench
InventorIsabel HÜNIG Carsten Schulz Helga Guthmann Ralf Kloos
ES2595114B1:Sensor, probe and equipment for chemical demand measurement
Abstract
Sensor, probe and equipment for the measurement of chemical demand for soluble oxygen based on amperometric detection for water quality control applications. # Sensor (1), probe (10) incorporating said sensor and equipment (20) incorporating the probe for the measurement of chemical demand of soluble oxygen based on amperometric detection for water quality control applications, the sensor being provided with an external metal surface intended to be immersed in a water sample, comprising a layer of a composite material of multipared carbon and polystyrene nanotubes and an inorganic catalyst, the inorganic catalyst being preferably a nanopowder of CuO and AgO.
Other languagesSpanish
InventorCésar Fernández Sánchez Manuel Gutiérrez Capitán Antonio Baldi Coll Cecilia JIMÉNEZ JORQUE Raquel GÓMEZ GUTIÉRREZ Jordi Cros Herrero Virginia GARCÍA DEL PUERTO
Current Assignee Adasa Sist S A U Adasa Sistemas Sau
KR20160139185A:Water quality monitoring devices with Internet capabilities things
Abstract
The present invention relates to a water quality monitoring apparatus capable of real-time monitoring and management of a measurement-related, measurement-related, and abnormality-related relation in real time through an administrator’s and a management apparatus through an object Internet function, And an object of the Internet of Things to enable real-time interactive communication using a management device and the Internet or a mobile communication network in order to manage abnormality signals, contrast judgment values, automatic and manual, Internet water quality sensor and water quality measurement sensor which measures various characteristics of water quality are connected to provide real-time conversation using management device and Internet or mobile communication network for measurement value of water quality characteristics.
Other languagesKorean
Inventor길주형
US20200025740A1US20200025740A1:Electrochemical method for detection and quantification of organic compounds in water
Abstract
Method and system for detection and quantification of oxidizable organics in water. The method involves the partial electrolytic decomposition of the oxidizable organics in a short time frame, preferably less than five seconds, and does not involve the use of toxic reagents. The system includes an electrochemical sensor probe that, in turn, includes a boron-doped diamond microelectrode array. The system additionally includes an electronic transducer and a computing device. The system utilizes an analysis technique to convert sensor signal to a result that can be correlated with COD or BOD values obtained by standard methods. The method and system are particularly suitable for, but not limited to, use in monitoring of water quality at wastewater treatment plants. By employing the method before and after adding aerobic microorganisms to the sample, the method may be used to distinguish biologically oxidizable organics from total oxidizable organics.
InventorBadawi M. Dweik Avni A. Argun Katherine E. Harrison
Current Assignee Giner Inc

Videos

COD (Chemical oxygen demand) – Indicator for water pollution
COD – Definition and meaning
Chemical Oxygen Demand (COD)
Chemical Oxygen Demand (COD) Measurement

CHAPTER 6:

Buy Chemical Oxygen Demand (COD) Sensor

The factories of smart sensors are all over the world. How can we choose the most suitable one?

When you come to this page, ZATA ZWQ-COD1 Sensor has appeared in front of you.

I believe that when you finish reading the introduction below, you will make the right purchase decision.

Model	ZWQ-COD1
Measuring Principle	Ultraviolet Absorption
Measure Range	0~500mg/L；0~500NTU
Measure Resolution	0.01mg/L；0.01NTU
Measure Accuracy	±7%
Interface	RS485（Modbus RTU）
Material	316L Stainless Steel Shell
Electrode Cable	3m
Electrode Dimension	D32mm L190mm
Power	DC12/24V

Learn More Request A Quote

CHAPTER 7:

Future of Chemical Oxygen Demand (COD)

As described above, COD monitoring method will become more and more convenient in the future.

It will become an indispensable part of our life.

Detection efficiency: the pre manual detection method takes a long time, and has the influence of secondary pollution. In the future, the detection technology must be the combination of multiple technologies to greatly improve the detection efficiency.
Maintainability: at present, there are too many manual detection processes, even with instrument detection, regular intervention by personnel is also required. In the future, with the development of AI technology, maintainability will be reduced through Internet of things technology, Including chemical oxygen demand calculation.
Real time online: compared with the timeliness of manual detection, detection is relatively backward. Through the development of Internet of things technology and 5g, the online real-time monitoring should be the main direction of COD detection.
Detection principle: compared with reagent detection, optical detection is a future development direction. Compared with single band detection, there are still some errors. The detection efficiency can be greatly improved by means of multi spectrum detection.

CHAPTER 8:

Chemical Oxygen Demand (COD) FAQs

Here are some common questions about Chemical Oxygen Demand. We will update them regularly through customer feedback.

I hope you can find the answers here. If you have more questions, please email to us.

What is A COD Sensor?

A cod sensor which could measure Chemical Oxygen Demand in water. Mainly use the principle of Ultraviolet Absorption.

What does Chemical Oxygen Demand indicate?

The chemical oxygen demand (COD) indicates the amount of oxygen which is needed for the oxidation of all organic substances in water and is thus an important indicator for water analysis.

Why is Chemical Oxygen Demand important?

Chemical Oxygen Demand is an important water quality parameter because, similar to BOD, it provides an index to assess the effect discharged wastewater will have on the receiving environment.

What is chemical oxygen demand in water?

The chemical oxygen demand (COD) is a measure of water and wastewater quality. The COD test is often used to monitor water treatment plant efficiency.

What is meant by chemical oxygen demand?

COD or Chemical Oxygen Demand definition. … Chemical oxygen demand (COD) is a measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals such as Ammonia and nitrite.