Application of Automatic Online Measuring Instrument in Sewage Treatment
Time:2022-11-24 Read:347
Reading guide: With the implementation of green environmental protection concepts and measures such as "two mountains" and "ten rivers", China's sewage treatment standards are becoming more and more strict, so all walks of life need to upgrade the original sewage treatment system equipment, which further increases the complexity and professionalism of related processes and equipment, and the task of operators is gradually increasing. With the development of automation technology, automatic online detectors have been used in the field of sewage treatment, which brings great convenience to sewage treatment.

Structural features of automatic online detection instrument

In the process of sewage treatment, the automatic instruments have the characteristics of simple operation, high definition, accurate measurement, etc. The main types can be roughly divided into two types: component analysis instruments and thermal instruments. Among them, the component analysis instrument, also known as the water quality analysis instrument, can detect dissolved oxygen, pH value, sludge concentration, and other components, including dissolved oxygen instrument, online BOD, and COD instrument, which have various forms and strong specificity; Thermal instrument is a kind of instrument to detect thermal work, which belongs to the physical measuring instrument and can detect pressure, liquid level, temperature, etc., including pressure instrument, temperature instrument, flow, and liquid level instrument, etc. 

The automatic online detection instrument is mainly composed of three parts: sensor, transmitter, and display. The sensor mainly detects and analyzes analog quantities, and uses signal detection methods for analysis; The transmitter mainly converts the signal detected by the sensor into the current signal and transmits it to the PLC, which is the programmable controller; The function of the display is to display the result parameters online through the screen so that the staff can immediately operate and read them. These three parts are an organic whole that is closely combined. The three parts work together to achieve online accurate measurement. At present, they have been widely used in wastewater treatment, playing a very positive role.

Application of automatic online detection instrument in sewage treatment

In China, wastewater treatment generally includes three stages: primary treatment stage, secondary treatment stage, and tertiary treatment stage. The wastewater is treated by grid filtration, sedimentation tank, biofilm method, activated sludge method, coagulation sedimentation method, activated carbon adsorption method, and other measures to finally meet the wastewater discharge standard, i.e., primary (A, B), secondary and tertiary, For example, the allowable discharge standard of Class I (Class A) of Chemical Oxygen Demand (COD) is 50 mg/L, Class B is 60 mg/L, Class II is 100 mg/L, and Class III is 120 mg/L, as well as biological oxygen demand, suspended solids, pH value, animal and vegetable oils, etc. The use of automatic online detectors can detect and record changes in water quality online and automatically, and conduct alarm processing to facilitate people's processing, greatly reducing the workload and difficulty of the work team, improving work efficiency, and reducing pollution.

Application of Automatic Online Measuring Instrument in Sewage Treatment

Automatic flow measuring instrument

In wastewater treatment, the automatic flow detection instrument plays a very important role. It can automatically analyze various data information in wastewater treatment, identify key parameters such as water inflow and outflow, sludge return flow, aeration volume, and gas production, and conduct real-time monitoring to provide detailed data support for wastewater treatment, so as to control the operating conditions of wastewater treatment equipment. In wastewater treatment, water volume is a very critical parameter. Accurately mastering the water inflow and outflow can effectively improve the control of the wastewater treatment process and the anti-impact ability of hydraulic load. The commonly used automatic flow measuring instruments include ultrasonic flowmeters, electromagnetic flowmeters, and differential pressure flowmeters.

(1) Ultrasonic flowmeter, mainly used in pipeline and channel measurement can effectively solve the shortage of traditional flow measurement in which measuring equipment such as flow troughs or weir plates can not reflect the flow change in real-time. It can directly understand the real-time flow and cumulative flow change of water level on the site or on the display, providing convenience for wastewater treatment. It has the advantages of no need to drill holes, no need to cut off the flow, good stability, and no additional costs The advantage of direct installation is that the detection effect in large diameter pipelines is particularly excellent, and it will not interfere with various data information of fluid and can be directly output as standard DC signal.

(2) The electromagnetic flowmeter is mainly used in the detection of excess sludge flow and return sludge flow. The electromagnetic flowmeter can be directly installed in the extra sludge pipeline and return sludge pipeline. The staff can judge the working conditions of the excess sludge pump and return sludge pump according to the parameter information displayed in the instrument, which can effectively get rid of the problem that it is impossible to judge the working status of the submersible pump in the past. The installation is convenient Advantages of convenient maintenance.

(3) Ultrasonic liquid level difference meter can calculate the liquid level difference between the front and back of the screen and the blocking rate of the screen through detection. In actual work, the ultrasonic liquid level difference meter can be directly installed on the coarse screen and the fine screen, and the relevant data can be transmitted to the PLC for analysis. If the detected liquid level difference exceeds the specified value, it indicates that there is a problem with the screen, which needs to be checked in time. Clean the garbage inside the grid and properly treat it to ensure the normal passage of wastewater and prolong the service life of the equipment. 

There is also an ultrasonic level gauge, which is a way to adjust and optimize the lift pump according to the amount of wastewater. It has the advantages of reducing the fatigue degree of the lift pump and extending the service life of the equipment. It is mainly installed at the position of the inlet pump well. The ultrasonic level gauge will directly transmit the detection data to the PLC and the upper computer for comprehensive system calculation and analysis. Based on the analysis results, the program control mode will be optimized to strengthen the automatic control level of the lift pump.

Automatic flow measuring instrument

Online analyzer

Among the automatic detection instruments, the online analyzer is a very critical component, which needs to analyze many parameter information such as dissolved oxygen, sludge concentration, chemical oxygen demand, ammonia nitrogen, total nitrogen, total phosphorus, etc. Through the online analyzer, the above information can be directly detected and analyzed, providing accurate and detailed information for wastewater treatment. Standard online analyzers include dissolved oxygen meters, sludge concentration meters, chemical oxygen demand analyzers, and many other instruments. Different instruments have different advantages and characteristics.

Dissolved oxygen meter

In wastewater treatment, the biofilm method, aerobic anaerobic microbial treatment method, activated sludge method and other processes will be used. Dissolved oxygen in water is an important factor to maintain microbial life activities. The dissolved oxygen meter can be used to detect dissolved oxygen in the water in real time, which can maintain microbial activity according to the actual situation and optimize the biochemical capacity of bacteria. Moreover, the automatic control system can reasonably control the operation of the aeration rotary table according to the results detected and analyzed by the dissolved oxygen meter, such as startup and shutdown. It has the advantages of saving energy and protecting equipment. It is the core of the wastewater treatment process and is closely related to the system adjustment. It is generally installed in the aeration tank to detect the dissolved oxygen in the aeration tank in real-time and directly transmit it to the PLC and the upper computer for system calculation and analysis.

Sludge concentration meter

In wastewater treatment, sludge concentration is an important indicator. Traditional sludge concentration detection is mainly based on experimental detection. The detection results are not timely and accurate, so it is difficult to achieve timely adjustment of the treatment process of excess sludge and returned sludge. The sludge concentration meter is installed in the aeration tank, which can detect the sludge concentration in real time and accurately, reduce the workload of the staff, and facilitate the optimization and adjustment of the amount of excess sludge and the timely adjustment of the amount of returned sludge treatment process.

Chemical oxygen demand analyzer

Chemical oxygen demand (COD) refers to the total amount of strong oxidant consumption per unit volume of sewage under certain conditions. It is an important indicator to measure the level of wastewater treatment. In practical work, the potassium dichromate measurement method is generally used for detection, which can reduce the deviation rate of detection data and improve the accuracy, effectiveness, and authenticity of data. However, there are also shortcomings such as expensive maintenance accessories, high reagent costs, and inability to repair immediately. The use cost is high.

Chemical oxygen demand analyzer

Temperature measuring instrument

Temperature measuring instruments, mainly platinum thermistors, a commonly used thermal sensor, temperature transmitter, and PLC, are usually used in the anaerobic digestion of wastewater treatment. The temperature monitoring point transmits information to the temperature transmitter to convert the thermal signal into an electrical signal, which is connected to the analog module. It has the advantages of simplifying the data processing and extraction process, monitoring the anaerobic digestion speed in real time, and helping anaerobic digestion.

Application effect and precautions of automatic online detection instrument

Actual application effect

First, in the process of wastewater treatment, in order to ensure the safe and stable operation of the system and reduce the failure rate, relevant personnel often take effective measures to help operators master and understand the relevant parameter system information, use these parameters to adjust and optimize the treatment equipment and process, improve the effect of wastewater treatment, and use automatic online detectors to understand the results of water quality changes in different time periods in real time, Provide detailed and reliable data information for wastewater treatment to ensure the safety and stability of the overall system. 

Second, the automatic online detection instrument is used to detect wastewater in real-time to facilitate the completion of various early control work. The actual measurement time of the online detection instrument is generally maintained at about 30 minutes. If there is a problem in the actual governance link, the instrument corresponding system will automatically send an alarm, and the operator will quickly locate the problem location, and adjust relevant parameters in time to ensure the overall water quality; Third, it is convenient to analyze and collect various data information and reduce and eliminate the impact of the sudden increase in sludge volume caused by seasonal changes.


(1) Regularly maintain and correct various instruments. In the long-term use process, the instrument will have measurement deviation due to various factors. It can be regularly maintained and corrected to ensure that the instrument is in the best operating state and the accuracy of measurement results;

(2) Pay attention to the cleanliness of measuring instrument sensors, and arrange for personnel to clean the sensors regularly. This is because the instrument sensors will be seriously polluted in the long-term wastewater treatment environment, especially the dissolved oxygen meter, sludge concentration meter, etc. that direct contact with wastewater, must be cleaned once a week to ensure their cleanliness, so as to ensure the authenticity and accuracy of the collected data. It should be noted that when cleaning, Soft materials shall be selected for cleaning as far as possible to avoid damaging the sensor;

(3) To ensure the stability of the instrument power supply, automatic detection instruments are easy to be damaged due to instantaneous electric shock. In the whole wastewater treatment system, if the instrument power supply is unstable, it is easy to damage the ultrasonic level gauge and ultrasonic level difference gauge, which will have a negative impact on the system stability.

Automatic Online Measuring Instrument in Sewage Treatment


To sum up, automatic detection instruments play an increasingly important role in wastewater treatment. With the continuous development of modern automation technology, their functions will become more prominent. Relevant personnel should increase the application of automatic detection instruments, apply automatic flow measurement instruments, online analysis instruments, temperature measurement instruments, etc. to wastewater treatment, and significantly improve the efficiency and quality of wastewater treatment.