How to reduce the cost of sewage treatment in sewage plants?

The energy consumption of the aeration system in the sewage plant accounts for about 50%-70% of the energy consumption of the whole plant, which is a key link in reducing the cost of sewage treatment in the sewage plant. As we all know, the operation and control characteristics of sewage treatment plants are different from other reaction systems. The sewage treatment process is a 'non-linear, large lag' system. At present, the common biological tank aeration control loop adopts DO-valve adjustment or PID fixed value adjustment. This control method Practice has proved that there are great shortcomings. Conventional PID control not only has a large hysteresis effect, but the control process is easy to cause system oscillation. According to incomplete investigations, there are few domestic cases where this control method is used to achieve stable operation. Many sewage plants have gradually changed from 'automatic' to 'semi-automatic' in the beginning, and even become manual 'measurement control' in the end. Therefore, in recent years, people have begun to pay attention to and try to adopt 'precision aeration' technology, but some problems exist or appear in the implementation process. The principle diagram of precise aeration control is shown in the figure below. At present, many domestic companies have provided services for precise aeration systems. Although the technical details, control methods and principles are quite different, the basic principles are similar, that is, to achieve 'on-demand aeration' and adopt a closed-loop control system. It not only collects process online monitoring data such as biological pond DO, but also collects water quality indicators such as NH3-N as feedback control signals to participate in system control. In addition, in terms of feedforward, the influent flow rate Q and influent water quality indicators, such as COD, NH3-N, etc., are collected. This forms a 'feedforward-feedback' closed-loop control loop. In terms of closed-loop control, Mr. Liu suggested introducing NH3-N or even PO4-P into the control loop. He believes that DO is just a process indicator, and what we control is actually the effluent quality indicator. The control system not only performs individual DO control on each reaction zone of the biological pond, but also performs feedback control on the effluent NH3-N.　　 The effectiveness of 'precision aeration' technology is facing various tests, and some people even think that precision aeration is a 'commercial hype.' Dr. Liu Zhixiao believes that there are four reasons for the above situations and phenomena. First, there is a disconnect between the program design link of the automatic control system of the sewage plant and the requirement of precise aeration technology, that is, the automatic control program of the design institute often adopts the traditional 'DO-valve opening' adjustment method, and the embedding is not considered at the beginning of the design. Precision aeration technology. The main reason is that precision aeration technology is often mastered by some professional companies, and owners often lack experience in this area or do not want to increase this part of the investment. Therefore, it is difficult to stably achieve precise aeration and achieve energy-saving purposes according to conventional aeration control methods. For the retrofit project, it is really not easy to implement a new blast aeration control loop based on a precise aeration algorithm in the original system. Therefore, Dr. Liu suggested that the precise aeration technology should be integrated into the entire investment scope of the wastewater treatment plant as much as possible during the design and equipment procurement of the wastewater treatment plant. The second is that precise aeration technology depends on high-quality hardware equipment, such as air linear control valves (such as diamond-shaped control valves), high-quality DO instruments, etc., and this part of the investment is relatively large, whether it is for new construction or renovation. All need to be considered, and the conventional electric butterfly valve can not achieve precise control of the aeration volume.　　 Third, the precision aeration system requires high-quality operation and maintenance. Even if many sewage plants have hardware, the management often fails to keep up. This is also an important reason why the precision aeration system cannot achieve the established functions. Therefore, the above conditions are indispensable for the implementation and realization of the predetermined effect of precise aeration in the sewage treatment plant. Fourth, the precise aeration technology relies on relatively reliable control algorithms and software programming. At present, there are many algorithms and implementation methods based on precise aeration. The algorithms of different companies are also 'different' or even 'innovative'In fact, these different implementations are based on the control principle, there are big differences, so the implementation effect and the stability of the control process are definitely different. At present, the mainstream precision aeration system of sewage treatment plants is still based on the precise control of the DO set value of the biological pond. In fact, this kind of control has very large technological and technical shortcomings. Therefore, some advanced international control systems are gradually adopting online water quality meters based on NH3-N, NO3-N, TP, etc. to participate in process control. Of course, this requires high-quality, high-stability sensors and maintenance standards.