According to the classification of sewage sources, sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production wastewater includes industrial wastewater, agricultural wastewater, and medical wastewater, while domestic wastewater refers to the complex mixture of various forms of inorganic and organic matter produced in daily life, including:

① Floating and suspended solid particles of varying sizes;

② Colloidal and gel like diffusers;

③ Pure solution.

According to the quality of water pollution, there are two types of water pollution: one is natural pollution; Another type is anthropogenic pollution, which currently poses a significant threat to water bodies. Water pollution can be mainly divided into three categories based on the different impurities of pollution: chemical pollution, physical pollution, and biological pollution. The pollutants mainly include:

(1) Untreated industrial wastewater discharged;

(2) Untreated domestic sewage discharged;

(3) Agricultural wastewater that heavily uses fertilizers, pesticides, and herbicides;

Industrial waste and household waste piled up by the river;

Soil erosion;

Mine wastewater.

There are many methods for treating sewage, which can generally be summarized as physical, chemical, and biological methods.

Sewage treatment plants: Some people have investigated more than 100 large treatment plants and found that there are many serious problems, such as insufficient funds, high costs, low efficiency, etc. Generally, the efficiency is less than 70%, with only 40% being low.

The cost and energy consumption of sewage treatment are generally high energy consumption and low efficiency.

In 2013, urban domestic sewage discharge has become the main source of urban water pollution in China. Domestic sewage treatment is currently and in the future a top priority for urban water conservation and environmental protection. This requires us to make the construction of domestic sewage treatment facilities an important part of urban infrastructure, and it is an urgent matter.

With the development of technology, direct utilization of sewage has become possible, and the use of sewage source heat pump systems for the utilization of urban primary sewage.

The so-called raw sewage refers to the direct discharge of untreated domestic and industrial wastewater from cities. At present, the utilization method is to directly enter the sewage source heat pump system for heat exchange, and use the raw sewage to cool and heat indoor buildings in the city while consuming a small amount of electricity. There are several technical difficulties to overcome in the reuse of sewage: blockage, corrosion, and heat exchange efficiency.

The sewage source heat pump system consists of two parts: a sewage heat exchanger and a sewage source heat pump. The urban raw sewage directly enters the sewage heat exchanger for heat exchange, and the heat exchanged is transferred from the heat pump inside the sewage source heat pump to the indoor environment.

The advantages of reusing urban sewage are energy conservation, environmental protection, and pollution-free.