The future development trend of COD online monitor

I. Analysis of environmental management requirements for COD on-line monitor:

1. Early requirements: compliance monitoring of chemical oxygen demand and construction of monitoring capabilities.

2. Current requirements: compliance monitoring of chemical oxygen demand, total emission reduction monitoring, total emission reduction statistics, emissions trading, information disclosure, and environmental risk warning and forecasting.

3. The requirements of environmental management require that the data of the online monitor is accurate and the higher the frequency, the better.

4. With the rise of the economic index and the deterioration of the environment, the current upgrade of pollution control facilities requires that the lower limit of measurement of on-line monitors is getting lower and lower.

Second, analysis of the status of COD online monitor:

1, data accuracy varies

At present, the data of COD online monitor can't meet the needs of law enforcement.

Cause 1 There are many methods for analyzing COD on-line monitors in the market:

Potassium dichromate (titration method, colorimetric method), UV method (single spectrum, double spectrum, full spectrum), TOC method (wet method, combustion method), advanced oxidation method (hydroxy radical oxidation method), and the like.

Cause 2 is caused by problems such as sampling conditions, laboratory analysis methods, and on-site instrument operation supervision and quality control.

2, monitoring frequency can not meet the total emission reduction and other needs

At present, the mainstream COD on-line monitor is mainly based on the potassium dichromate method, and its single analysis cycle is about 35-60 minutes, which cannot be truly real-time online. There is a prominent contradiction in view of current environmental management requirements. However, other analysis methods such as UV method can realize real-time online, but due to the high frequency of water quality change, etc., a good conversion mathematical model cannot be found and the accuracy of its real-time data is also controversial. TOC, Advanced Oxidation also has such problems.

3, monitor the secondary pollution of waste

The COD on-line monitoring instrument based on the potassium dichromate method has a large amount of waste liquid. If it is not properly disposed, the secondary pollution will be a very serious hidden danger. The ultimate demand for environmental management is to better improve water quality and not for COD data.

4. The lower monitoring limit after the increase of emission standards has become a challenge

Under the circumstance of deteriorating environment, the upgrading of treatment facilities also raises new requirements for the lower limit of the COD on-line monitor. Many potassium dichromate monitors have been unable to output stable and accurate monitoring data, such as the emission standards of Class A. The COD reached 30 mg/l, which is undoubtedly a great challenge for the original national standard potassium dichromate method that is 50 mg/liter. The TOC method and UV method may have some advantages here.

5. Questioning the authenticity of data

At present, the question of the authenticity of instrument data due to the supervision of the instrument site operation is frequently heard. Some provinces have begun to implement the dynamic control of the instrument: to establish a unified parameter range of the instrument, and to monitor the authenticity of the field data through the data range.

III. Looking into the Future of COD Online Monitors

Obviously, there is a big difference between the demand and the status quo. So, what will the COD monitor be like in the future?

1. The self-learning COD on-line monitor combined with potassium dichromate method and UV method can effectively solve the problem that the fixed UV mathematical model cannot be accurately monitored due to the change of on-site water quality, and the UV correction is carried out by a very small amount of potassium dichromate method. Fixed mathematical model. Under the ideal condition, the secondary pollution amount of the waste liquid will greatly reduce the amount and effectively solve the problem of potassium dichromate method monitoring frequency and the accuracy of the UV method data, realizing accurate online and accurate production.

2. COD on-line monitor which is free of reagents and has high correlation with potassium dichromate method data. For example, COD in water bodies is oxidized by ozone with higher oxidation potential of potassium chromate, and the amount of ozone added, consumption, The mathematical model of the dissolved amount calculates the chemical oxygen demand value of the water body. Under ideal conditions, it can realize no secondary pollution, rapid oxidation, real-time online, and accurate data.

3. Integrate the COD on-line monitor with the quality control instrument, sampler, sample retention device, PH, dissolved oxygen, conductivity, flow meter, etc. to form a COD online monitoring system, build a cloud platform and collect system big data through the cloud The calculation finds the correlation of data in each part of the system, so as to effectively perform total emission reduction statistics and environmental risk warning and forecasting.