How to transform the sewage combined pipe in the old city? What difficulties will we face? What are some good suggestions?

The renovation of sewage combined pipes in the old city is a very complex project. The renovation measures should be based on the specific conditions of the city and local conditions, taking into account sewage quality and quantity, hydrology, meteorological conditions, water body sanitation conditions, financial conditions, Factors such as on-site construction conditions, combined with urban drainage planning, ensure that the water body is reduced as much as possible, while making full use of the original pipes and channels to achieve the dual goals of protecting the environment and saving investment.

At this stage, there are four main ways to transform the old combined drainage pipe system, which are described below:

(1) Change the old combined system to a diversion system

Changing the old confluence system into a diversion system is a thorough transformation method. Due to the implementation of rainwater and sewage separation, all sewage can be directed to the sewage treatment plant for treatment, fundamentally eliminating the direct discharge of sewage from polluting water bodies. At the same time, since rainwater does not enter the sewage treatment plant, the water quality and quantity of the treated water can be maintained within a small range of change, ensuring the relative stability of the effluent water quality and making it easy to achieve discharge standards.

To implement the diversion system, the requirements for the current conditions are relatively high. Whether it is a residential area or an industrial enterprise, its internal pipeline system must be sound, requiring independent sewage pipeline systems and rainwater pipeline systems to facilitate connection. into the corresponding urban sewage and rainwater pipe networks; at the same time, the cross-section of the urban street is required to have sufficient space to allow the laying of new pipes. In general, cities have been under construction for a long time, underground pipelines have basically taken shape, ground buildings are crowded, and roads are narrow. If the confluence system is changed to a diversion system, there will be many practical problems such as large investment and construction difficulties, which will be difficult to achieve in the short term.

(2) Retain part of the combined pipes and implement an interception-type combined system

In most cities, if the water environment has sufficient self-purification capabilities, they basically adopt an intercepting-type combined drainage system and retain In some combined pipes in the old city, interception main pipes are laid along the water bodies around the city to intercept the combined sewage. Depending on the development of the city, the pipe network will be gradually improved and changed to a diversion system. This transition method has been widely used and achieved good results due to its relatively small project volume, investment savings, easy construction, and quick results. Not long ago, I designed and completed the Chaohu City Sewage Plant supporting pipe network project. The old city has been built for many years, and the above-ground buildings and underground facilities have taken shape. It is not suitable for large-scale diversion system reconstruction. However, there are abundant rivers such as the Huancheng River and the Tianhe River in the city. The water body can be used. According to the actual local conditions, an interception-type combined drainage system has been adopted in the old city.

In the dry season, the intercepting combined drainage system can send all sewage to the sewage treatment plant. During the rainy season, only part of the combined sewage can be transported to the sewage plant for treatment through interception facilities. The sewage exceeding the interception volume is discharged into nearby water bodies, which will inevitably cause local and short-term pollution to the water body. The sewage entering the treatment plant is mixed with A large amount of rainwater causes large fluctuations in the quality and quantity of raw water, which is bound to have an impact on the treatment units of the sewage plant. This puts forward higher requirements for the treatment process of the sewage plant.

(3) On the basis of the interception-type combined system, set up combined sewage regulation and storage structures

In some cities, the surrounding water bodies are sparse, the environmental capacity is limited, and the self-purification ability is poor, so it is not allowed The combined sewage is discharged directly. In this case, a combined sewage storage structure can be set up at an appropriate location in the interception main pipe. The combined sewage that exceeds the transfer capacity of the interception main pipe and the treatment capacity of the sewage plant can be introduced into the storage structure for temporary storage until heavy rains. Afterwards, it is lifted to the main interception pipe through the sewage pump, and finally enters the sewage plant for treatment, basically ensuring that the water body is not or less polluted.

It should be pointed out that this kind of storage regulation and storage structure often covers a large area, and the amount of rainwater is not a fixed value. It is difficult to reasonably determine the volume of the combined sewage regulation and storage structure; furthermore, the regulation and storage The combined sewage volume is finally raised to the main interception pipe through sewage pumps (except for a few cities with height differences), which causes inconvenience in daily operation, maintenance, and management. It also reduces the load and operating costs of the sewage treatment plant, so it is not necessary It is recommended to adopt the diversion system and it will only be considered after fully demonstrating the possibility of implementing the diversion system.

(4) Treat overflow mixed sewage on the basis of the interception-type combined flow system

Similar to the previous situation, if the self-purification capacity of the water body around the city is limited, the water environment will be relatively poor. It is fragile and adopts an interception-type combined drainage pipe system. The overflow combined sewage must be treated before it is discharged into the water body.

In view of the characteristics of large volume and low concentration of combined sewage, primary treatment can be adopted, and the treatment processes of screening, coagulation and sedimentation, and chlorine disinfection can be selected. After the combined sewage is treated, the concentration of pollutants can be significantly reduced, thereby greatly reducing the pollution to water bodies.

Similarly, because this measure considers the treatment of rainwater, it has similar shortcomings as the previous situation: daily operating costs are high, and the decentralized treatment facilities are far away from the city’s centralized sewage treatment plants, making operation, maintenance, and management difficult. There are many inconveniences.

According to the technical policy requirements for urban water pollution control in my country, the transformation, adjustment and construction of urban municipal drainage pipe networks should be strengthened to divert rainwater and sewage and create conditions for centralized treatment of urban sewage. Therefore, for the reconstruction measures of the old combined drainage pipe system in the city, the diversion system should be given priority. In cases where implementation is difficult, the interception type combined drainage pipe system can be considered. The third and fourth situations are improved on the basis of the interception-type merging system, and are proposed in response to higher environmental requirements, and have certain particularities. In fact, in most cities in our country, the construction of old urban areas was generally in the era when the merger system was prevalent. They are deeply marked by the times and it is difficult to change the status quo in the short term. Therefore, at this stage, our country’s transformation of the old merger system in old urban areas , the interception-type combined drainage system is the most commonly used method.