This year, Hangzhou launched the construction of "zero sewage discharge area" version 2.0, targeting at realizing rain sewage diversion.
However, one of the major problems is that some washing machines for families are set up in the balcony, especially in some small flats, which means the sewage caused by laundry is directly discharged into river with rain, since most of the pipelines in the balcony are designed for rainwater only.
If laundry sewage is directly discharged into the river, a lot of problems will occur. Synthetic detergents, for example, can produce a lot of foam in water, hinder water and air contact, reduce dissolved oxygen in water and damage the ecological environment. And the phosphorus in washing powder can cause eutrophication in rivers and algal reproduction. These plants release toxic and odorous gases such as methane, hydrogen sulfide, ammonia and so on, which make the water quality turbid and stink, make the water lack of oxygen and threaten aquatic life such as fish and shrimp, and pollute the water.
Previously, a statistics made in Hangzhou shows that balcony sewage had become the largest pollution source in the main urban rivers, accounting for 30% of the total sewage. Therefore, although the water quality of the rivers in Hangzhou has obviously been improved since the "five Water Governance"project, there are always some watercourses that will rebound from time to time. The reason is that many pipelines have not diverted rain and sewage.
But how to divert the laundry sewage?
The former drainage system will turn to the special sewage pipe, connecting to the city sewage pipe network and running to the sewage treatment plant. At the same time, a new special rainwater pipe will be set up, all the sky water wells and the road water wells will be connected to the newly built Rain Water system, and its exit will be connected to the urban rainwater pipe network. To put it simply, the balcony sewage confluence system must carry on the diversion transformation; the newly built Rain Water system must strictly carry out the rain pollution dis-tributary, to establish the independent drainage system for the balcony sewage.