Most wastewater treatment plants currently use the activated sludge method to treat wastewater, which has been used for more than 100 years and has stood the test of time. This treatment method uses microbial metabolism to degrade pollutants in water, and microorganisms play an important role in the removal of pollutants from wastewater. To ensure the reproduction of the microbial community must meet the necessary conditions for its survival, the oxygen content in the wastewater is critical, therefore, to ensure that the microorganisms in the wastewater are effectively reproduced, the oxygen content in the wastewater should be controlled within a certain range, too low or too high aeration will affect the effectiveness of the treatment of wastewater quality.
The aeration method is a common method of sewage supplemental oxygen, aeration equipment is widely used in sewage treatment equipment, not only because it can provide sufficient dissolved oxygen, and will not cause secondary pollution of the water environment, but also has the function of mixing and stirring. The energy consumed by the aeration method accounts for more than half of the total energy consumption of wastewater treatment. With the gradual increase in energy saving and emission reduction in wastewater treatment plants and the requirement to reduce energy consumption, there is an urgent need to change from conventional automatic control and manual regulation to precise and intelligent control. Precise control of the oxygen content in the wastewater can not only contribute to the stable operation of the system but also further reduce energy consumption.
Wastewater treatment plant aeration precision control concept and the need
Wastewater treatment plant aeration precision control concept
The aeration system as the main energy consumption unit of the wastewater treatment plant, its control level for the overall energy consumption of the wastewater plant, and the effluent water quality have a very important impact. Due to fluctuations in influent water quality and quantity, traditional aeration control often has a lagging effect and is not ideal. Considering the demand for ecological environmental protection in urban development, the use of aeration technology in the wastewater treatment process should follow certain principles, which require the use of online monitoring instruments to collect signals such as wastewater volume, gas volume, dissolved oxygen, blower power and pressure in real-time.
According to the control theory, to achieve accurate aeration, first of all, to control the air input, air input after the aeration device sprayed will form bubbles, these bubbles have different volumes, in the sewage constantly floating up, to achieve accurate control of the aeration volume. Secondly, the temperature of the air should be controlled so that the air has a certain condensation effect in order to facilitate the formation of water droplets to enhance the precise control of aeration, which is required for the bubble system to have a high control accuracy so that the effectiveness of aeration can be enhanced and the precise control of aeration can be finally realized. Accurate aeration can achieve more stable operation of the biological treatment system of the wastewater plant as well as the effluent water quality, and more importantly, more energy efficient than manual control.
The necessity of precise control of the total amount of aeration in wastewater treatment plantsAccording to the actual situation of China's wastewater treatment plants at this stage, the aeration control accuracy is generally at a low level, leading to generally high energy consumption in wastewater treatment plants, in order to improve energy utilization, the precise control of the total amount of aeration is very necessary.
Wastewater treatment plants control the total amount of aeration by controlling the blower dampers and using the dissolved oxygen content as a reference indicator. Most wastewater treatment plants take manual methods for blower control, and operators repeatedly adjust the size of the blower according to the dissolved oxygen index, which is limited by the level and experience of the operator, making it difficult to guarantee the stability of water quality and wasting resources more obviously. In the control of aeration, the load of the wastewater treatment plant is constantly changing, there is no fixed rule to follow, and the dissolved oxygen fluctuates greatly, requiring operators to adjust repeatedly, not only the labor intensity is greater, but the accuracy of control is also lower.
To precisely control the dissolved oxygen content, the online detection method can be introduced to detect the oxygen content through advanced sensors to provide real-time data for the control of aeration volume and help the staff to accurately control the size of the aeration volume, but under actual working conditions, the location and number of oxygen content sensors have a greater impact on the measurement accuracy, and the monitoring results have a certain lag due to the influence of electronic equipment transmission.
Therefore, the accurate control of total aeration should follow the law of aeration change in addition to the index of oxygen content, and develop a scientific aeration plan, so as to control the total aeration more accurately and meet the demand of protecting the ecological environment.
Problems in the precise control of total aeration in wastewater treatment plants
Automatic control and precise control are disconnected from each other
When developing a precise aeration program in a wastewater treatment plant, the control precision should be improved in a targeted manner, taking into account the actual situation. In some automatic control systems, there is still a problem of low control accuracy, which is caused by the relevant staff not having sufficient mastery of control technology, lacking working experience, and not having a solid theoretical foundation, leading to the inability to coordinate precise control with actual demand when aeration control, affecting the implementation effect of precise control.
Aeration precise control of the hardware conditions is high
At this stage, China's sewage treatment plant precision aeration control relies heavily on hardware equipment, the control system contains automatic regulating gas valves, flow meters, advanced oxygen sensors, and other equipment, these devices are required to have extremely high control accuracy, so the hardware cost is high, in the new sewage plant project, the investment for precision aeration control equipment has been high, there are certain difficulties in the project construction, which restricts the precision aeration The construction of precision aeration control.In addition, the maintenance requirements of various types of equipment required for precision aeration are also high, and instruments and valves may show large deviations after running for a period of time, which may lead to inconsistencies between the aeration volume and the actual demand if not corrected in time, easily causing the effluent water quality not to meet the standards. Traditional aeration control means and overly dependent on the staff's experience and responsibility, can not achieve aeration precision control, the normal operation of the wastewater treatment system caused a certain degree of impact.
Longer calibration time for precise aeration control
According to the current actual operation of China's wastewater treatment plants can be seen, most treatment plants use the activated sludge mathematical model as the calculation logic of the precise aeration control system, this algorithm requires the historical data of the treatment plant as a reference in order to predict the total amount of aeration to be performed, the calibration time of some key parameters is long and has a great impact on the control accuracy. Many wastewater treatment plants have experienced problems with substandard water quality, further increasing the difficulty of water quality treatment and making precise aeration control even more difficult.
Precision aeration technology classificationAeration technology has gone through two stages, respectively, the manual control stage and automatic control stage, automatic control stage mainly uses the constant oxygen content control method, and can be divided into two forms direct control fan and indirect control fan, manual control method can not achieve precise control of the total amount of aeration, energy waste situation is serious, later the technical staff introduced fuzzy control and neural network control and other advanced control methods, the development of automatic Control technology, and gradually to the direction of intelligent development. At this stage, the application of automatic control technology in China's wastewater treatment plants is still relatively small. With the continuous development of intelligent technology, programmable controller technology has gradually matured and model-based precise control technology has entered the practical application stage, occupying a dominant position in the field of automatic aeration control technology.
Combined with the development status of automatic aeration technology at home and abroad, the current stage of precise aeration control is mainly divided into two categories: biological model and hardware integration.
The biological model is mainly based on the model of microbial growth in water, and various sensors and monitoring equipment are installed in the wastewater treatment pond to monitor water temperature, oxygen content, microbial content, and other indicators to grasp the changes in water quality, and then a sludge model of the wastewater treatment pond is established to predict the air demand as a reference for controlling the blower output and adjusting the blower blowing volume in real-time. Theoretically, this method can achieve accurate oxygen content control, the requirements of various monitoring equipment are high, and if the monitoring indicators and the actual difference is large, the calculation results will be seriously distorted, resulting in oxygen demand is not accurately controlled, resulting in abnormal water quality and other situations. The AVS precise aeration control system developed by this company is based on the above theory for precise control of aeration.The precise aeration technology used in the wastewater treatment process can significantly reduce the energy consumption of wastewater treatment plants, improve the discharge water quality and obtain a stable water quality index. As an important part of the protection of the urban ecological environment, the energy consumption of wastewater treatment plants has been a concern in many aspects, the aeration system accounts for more than half of the total energy consumption of wastewater treatment plants, the precise control of aeration is a good way to reduce energy consumption and improve water quality, with the growing popularity of environmental protection concept, as well as the development of various advanced technologies, the application of precision aeration system has been realized, in the future It will be recognized by more wastewater treatment plants in a period of time.