According to the perspective of sewage sources, sewage can be defined as a liquid or water containing waste discharged from residential, government, commercial or industrial areas, mixed with groundwater, surface water, blizzards, etc. There are many types of sewage, and correspondingly, there are many technologies and processes to reduce the impact of sewage on the environment. According to the source of sewage, it can be divided into four categories.

*Type 1: Industrial wastewater comes from wastewater from manufacturing, mining, and industrial production activities, including runoff leachate from industrial or commercial storage and processing, as well as other wastewater that is not domestic sewage.

Type 2: Domestic sewage comes from residential, office buildings, government agencies, or similar sources of sewage; Sanitary sewage; Sewer wastewater, including industrial wastewater mixed with domestic sewage in the sewer system. Garbage, various atmospheric particulate matter deposition, etc., enter the water environment through surface runoff, soil erosion, farmland drainage, and other forms. It has the characteristics of dispersion, concealment, randomness, latency, accumulation, and fuzziness, making it difficult to monitor, quantify, and research and control. Substances that cause pollution when water pollutants are discharged into water bodies.

Category 3: Commercial wastewater comes from commercial facilities and some components are non-toxic and harmless compared to domestic wastewater. Such as catering wastewater. Laundry wastewater, animal husbandry wastewater, and wastewater generated by hair salons.

Type 4: Surface runoff comes from rainwater, snow water, highway drainage, water from urban and industrial areas, etc. Surface runoff does not infiltrate the soil, but enters groundwater along streets and land.