Direct discharge combined system means that industrial wastewater, domestic sewage and initial rainwater are directly discharged into rivers and lakes through a pipeline, which leads to serious pollution of natural water bodies.
Interception and confluence system is to add an interception well and a branch pipe to the confluence pipeline, and the branch pipe is connected to the sewage treatment plant. Sewage is intercepted to the sewage treatment plant in sunny days, and mixed water of rain and sewage is also intercepted to the sewage treatment plant in rainy days. However, when the rainfall is too large, the sewage treatment plant is overloaded and can't handle a large amount of mixed water of rain and sewage, so it will overflow into the natural water body through the intercepting well, thus causing water pollution problems such as rivers, lakes and seas.
The rainwater and sewage diversion system means that rainwater is discharged into natural water bodies through rainwater pipes, and sewage enters sewage treatment plants through sewage pipes to realize rainwater and sewage diversion. However, this drainage system also has two problems. First, there is a phenomenon that pipelines are staggered and mixed, and sewage enters the rainwater pipe or rainwater enters the sewage pipe. Second, rain and sewage diversion can't solve the problem of non-point source pollution. When it rains, the ground garbage (such as garbage transfer stations, restaurants, auto repair and agricultural products) will be brought into rivers, lakes and seas through rainwater pipelines after the initial rainwater washes the atmosphere and the ground, resulting in non-point source pollution.
Therefore, before the rain and sewage were separated, most urban areas adopted the direct drainage combined system and the interception combined system, but neither the combined system nor the separated system fundamentally solved the problem that domestic sewage, industrial wastewater and initial rainwater entered the natural water body.
In recent years, many cities have begun to adopt the fourth generation drainage system-sewage separation. Through intelligent storage, normally discharged sewage and mixed sewage enter the sewage treatment plant for standard treatment in sunny days; Rainy sewage and dirty initial rainwater enter the sewage treatment plant for standard treatment, and clean middle and late rainwater is directly discharged into rivers, lakes and seas, which fundamentally solves the problem that domestic sewage, industrial wastewater and initial rainwater enter natural water bodies.
Its core is intelligent diversion, accurate pollution interception, peak regulation and storage, and intelligent water affairs, so as to realize real pollution removal and diversion, control pollutants entering natural water bodies within the tolerable range of self-repair and realize long-term cleaning of natural water bodies.