Determination principle of BOD analyzer method

In a nutshell:

BOD: Biochemical Oxygen Demand (BOD) indicates the amount of organic matter that can be metabolized and broken down by aerobic microorganisms. Because the content of such organic matter cannot be measured directly, and the microbial metabolic decomposition of organic matter requires respiration, which consumes dissolved oxygen in water, the amount of organic matter in water can be measured indirectly by measuring the change in dissolved oxygen in the water (which must be the amount of reduction).

Microbial metabolism takes time, generally about 5 days can reach more than 75% of the total BOD value (official data, but in fact, because it was the British health ** that proposed this concept at that time, 5 days is enough for any river in the UK to enter the sea, 6 days BOD is meaningless... If you want to get the total BOD value, it takes more than 20 days, which is a long time, so there is a unified indicator of BOD5. The 5-day biochemical oxygen demand (BOD) is used to characterize the relative magnitude of the degree of organic contamination of the water body.

For specific measurement steps and methods, please see.

Determination of the national standard five-day biochemical oxygen demand (BOD5) dilution and inoculation method GBT 7488-87

Determination of biochemical oxygen demand (BOD) by biochemical oxygen demand (BOD) Rapid assay for microbial sensors HJ T 86-2002

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BOD (abbreviation for Biochemical Oxygen Demand): Biochemical oxygen demand or biochemical oxygen consumption (generally refers to five-day biochemical oxygen demand), which is a comprehensive index that indicates the content of aerobic pollutants such as organic matter in water. The total amount of dissolved oxygen in the water is used to make organic matter inorganic or gasified due to the oxidative decomposition of organic matter in water due to the biochemical action of microorganisms.

Normally, it means that the water sample is filled with a completely sealed dissolved oxygen bottle, incubated in the dark for 5 days at 20, and the mass concentration of dissolved oxygen in the water sample before and after incubation is measured respectively, and the dissolved oxygen consumed per liter of sample is calculated by the difference between the mass concentration of dissolved oxygen before and after incubation, which is expressed in the form of BOD5. Its units are expressed in ppm or milligrams. The higher the value, the more organic pollutants in the water, and the more serious the pollution.

In order to make the test data comparable, a time period is generally specified, during which microorganisms are cultured with water samples at a certain temperature and dissolved oxygen consumption in the water is measured, generally using a five-day period, called five-day biochemical oxygen demand, which is recorded as BOD5. The higher the number, the more organic matter is in the water, and therefore the more polluted.

BOD, Biochemical Oxygen Demand (BOD) is an environmental monitoring indicator that is mainly used to monitor the pollution status of organic matter in water bodies. Generally, organic matter can be decomposed by microorganisms, but microorganisms need to consume oxygen when decomposing organic compounds in water, and if the dissolved oxygen in the water is not enough to supply the needs of microorganisms, the water body is in a polluted state. BOD is the indicator of environmental protection.

The determination of BOD was determined by GB7488-87 five-day biochemical oxygen demand determination method.

Principle of the tester When the water sample containing saturated dissolved oxygen enters the measurement tank and contacts with the biosensor, when there is no biodegradable organic matter in the water sample, a constant current is generated when the diffusion velocity (mass) of dissolved oxygen to the oxygen electrode reaches a constant level. When there is biodegradable organic matter in the water sample, the organic matter is assimilated by the microorganisms in the biofilm, and the cellular respiration of the microorganisms is also enhanced, and a part of the dissolved oxygen is consumed, so that the dissolved oxygen diffused on the surface of the oxygen electrode is reduced, when the diffusion speed (mass) of dissolved oxygen to the electrode in the water sample reaches constant again, a constant current is generated, because the difference between the two constant currents and the concentration of biochemically degradable organic matter in the water sample has a quantitative relationship, so the current signal is amplified by the microcomputer, After the analysis and processing, the BOD test results are directly displayed.

oxygen

demand

Abbreviated as BOD. It is a comprehensive indicator that indicates the content of aerobic pollutants such as organic matter in water. It describes the total amount of dissolved oxygen in water consumed when organic matter is oxidized and decomposed by microbial biochemical action to make it inorganic or gasified, and its unit is expressed in ppm (milligram liters).

BOD generally refers to the amount of organic matter that can be degraded by microorganisms, that is, the amount of degradable organic matter in wastewater.

Methods for determining BOD include:

1.Standard dilution.

This method is the most classic and the most commonly used. Simply put, it is to measure the difference in the amount of dissolved oxygen in the solution before and after five days of incubation at 20 1 temperatures. The calculated BOD value is called "five-day biochemical oxygen demand (BOD5)".

2.Biosensor method.

The principle is to make the water sample and air enter the flow pool and contact with the microbial sensor with a certain flow rate, when the diffusion speed of the bacterial film of the soluble and degradable organic matter in the water sample reaches a constant rate, the oxygen mass diffused to the surface of the oxygen electrode also reaches a constant and produces a constant current, because the difference between the current and the biochemically degradable organic matter in the water sample has a quantitative relationship with the reduction of oxygen, according to which the biochemical oxygen demand of the water sample can be calculated. The BoD5 standard sample is usually compared to calculate the BoD5 value of the water sample.

3.Activated sludge aeration and degradation method.

The control temperature was 30 -35, the activated sludge was used to force aeration to degrade the sample for 2 hours, and the stoichiometric oxygen demand before and after biodegradation was determined by potassium dichromate digestion of the biodegraded sample, and the difference was BOD. According to the results of the comparison experiment with the standard method, it can be converted to a BOD5 value.

4.Manometry.

In a closed flask, the dissolved oxygen in the water sample is consumed by microorganisms, and the microorganisms produce CO2 equivalent to the oxygen consumption due to respiration, and when the CO2 is absorbed, the pressure of the closed system is reduced, and the BOD value of the water sample can be obtained according to the pressure drop measured by the pressure.

In the field of sewage treatment, BOD is called: biochemical oxygen demand, which is one of the important pollution indicators of sewage.

It refers to the amount of free oxygen consumed by microorganisms in the process of decomposing and oxidizing organic matter in water under certain conditions of temperature and time, and the unit is mg l or kg m3

BOD analyzer, i.e., biological oxygen demand analyzer, is an instrument used to analyze the biological oxygen demand of a certain body of water. Biological oxygen demand (BOD) is the amount of oxygen consumed by microorganisms to grow in a certain amount of water, and is an environmental monitoring index, which is mainly used to monitor the pollution status of organic matter in water bodies.

Relative standard deviation: 5%.

Sensor Features:

A three-electrode integrated core sensor with a reference electrode using a KCl solution as the electrode solution.

Flow-through design: automatic switching device for liquid flow, automatic cleaning is convenient and fast.

Operating device: It can automatically switch on and off to realize unattended operation.

Microbial Film: Microbial Culture: BOD5 special culture with InterBio (EPA certification) technology.

Microbial film features: Laminated dry membrane, non-toxic and harmless.

Life of microbial film: Dry storage at room temperature for more than one year, activation life of more than 30 days.

Injection method: The liquid of this machine automatically switches to continuous injection, and 7 different samples are measured continuously, without the need for an external injector.

Control mode: It can be operated by local machine and controlled by microcomputer.

Software environment: Windows XP Chinese software。

Mode switching: Manual measurement is possible Automatic measurement mode switching.

Switch on and off mode: It can be automatically turned on and off.

Data storage: All data is automatically stored in the historian and can be used using Excel software.

When there is biodegradable organic matter in the water sample, the organic matter is assimilated by the microorganisms in the biofilm, and the cellular respiration of the microorganisms is also enhanced, and a part of the dissolved oxygen is consumed, so that the dissolved oxygen diffused on the surface of the oxygen electrode is reduced, when the diffusion speed (mass) of dissolved oxygen to the electrode in the water sample reaches constant again, a constant current is generated, because the difference between the two constant currents and the concentration of biochemically degradable organic matter in the water sample has a quantitative relationship, so the current signal is amplified by the microcomputer, After analysis and processing, the equipment that can directly display the BOD test results is called a BOD tester.