Preferred backwash filter process for large urban sewage treatment plants
Preferred backwash filter process for large urban sewage treatment plants
The preferred process for large urban sewage treatment plants is the conventional activated sludge process and its improved A/O process, A2/O process. At present, most of the large sewage plants in the world (including China) use the traditional backwash filter activated sludge process, A/O and A2/O methods, because this process has an irreplaceable advantage for large sewage plants:
1 The traditional activated sludge process, A/O and A2/O methods have the greatest advantages compared with the oxidation ditch and SBR process, such as lower energy consumption and lower operating costs. The greater the scale, the more obvious the advantage. For large-scale sewage plants, the annual operating expenses are considerable. For example, a sewage treatment plant with a scale of 40×104 m3/d, a 1 m3 sewage saving treatment fee of 1 cent, and a saving of 1.46 million yuan per year.
The reasons for the low energy consumption and operating costs of this process are: a. setting up the primary sedimentation tank, using physical methods to remove a considerable part of the organic matter and suspended matter in the sewage with minimum energy consumption and cost, reducing the secondary treatment load, and saving significantly. Energy consumption; b. Sludge uses anaerobic digestion, which is a recognized energy-saving process because of the significant aerobic digestion of the oxidation ditch and SBR process.
The capital investment of this process is generally higher than that of the oxidation ditch and SBR process, but as the scale increases, the infrastructure cost of the oxidation ditch and SBR also increases exponentially, while the investment in the conventional activated sludge process is smaller. The proportion increases and the gap between the two is getting smaller and smaller. When the sewage plant reaches a certain scale, the investment of the conventional activated sludge process is more economical than the oxidation ditch and SBR. Therefore, the larger the scale of the sewage plant, the greater the advantage of the conventional activated sludge process.
2 The main disadvantages of conventional activated sludge process, A/O and A2/O method are that there are many treatment units and complicated operation management. Especially, sludge anaerobic digestion requires high level of management. The biogas generated by digestion process is flammable and explosive gas. More security is required, which increases the difficulty of management. However, due to the large-scale sewage plant backed by big cities, strong technical force and high management level, it can meet this requirement, so the shortcomings of the conventional activated sludge process will not become a limiting factor.
According to the current reality, urban sewage treatment is in its infancy, regulations and systems are not sound enough, there is no clear regulation on sludge stabilization requirements, and because the drainage network system is not perfect, most urban sewage organic components are not high. In addition, the management of sludge anaerobic digestion and the utilization of biogas still lack mature experience, all of which reduce the economics of conventional activated sludge process, A/O and A2/O processes including sludge anaerobic digestion. Therefore, for urban sewage treatment plants of scale (10-20)×104 m3/d, it is sometimes more economical to use SBR and oxidation ditch processes. In this case, it is necessary to carry out detailed technical economics for various processes. Compare to determine the best process.