1. Reclaimed Water Can be Categorized into Two Methods Due to Its Varied Applications:
（1）The standard for potable water and its direct reuse in daily life: This treatment method is suitable for areas where water resources are extremely scarce, but the investment is high, and the process is complicated.
（2）Treat the water for other essential applications: Mostly used for toilet flushing, floor, and automobile cleaning, greening watering, fire prevention, general industrial water, etc. This is the standard procedure for water treatment.
2. Two Distinct Types of Reclaimed Water Treatment Processes
（1）Physical treatment method: The membrane filtration method is suitable for situations where water quality changes greatly. The main characteristics of this process are compact, easy to operate, and little influenced by load changes. Membrane filtration makes the separated solution flow along the surface of the filter membrane at a certain flow rate under the action of external force.
Solvents, low molecular weight substances, and inorganic ions in the solution pass through the filter membrane from the high-pressure side, and the filtered pure water enters the low-pressure side and is discharged as filtrate. The polymer substances, colloidal particles, and microorganisms in the solution are intercepted by the ultrafiltration membrane, and the solution is concentrated and discharged in a concentrated form.
This process is suitable for situations where the quality of sewage varies greatly. The commonly used methods are sand filtration, activated carbon adsorption, etc.
Physical treatment method defining features:
- Using hollow fiber ultrafilter for processing
- Advanced technology
- Compact structure
- Less land occupation
- Intermittent operation of the system
- Simple management
（2）Biological treatment method: This method is suitable for sewage with high organic matter content. Generally, biological treatment methods such as the activated sludge method, contact oxidation method, and biological turntable are used. It can also be used alone or in combination with several biological treatment methods, such as contact oxidation + biological filter, biological filter + activated carbon adsorption, rotary disc ten sand filter, and other processes.
This process has the advantages of a strong ability to adapt to hydraulic load fluctuations, less sludge generation, and easy maintenance and management.
3. Types of Reclaimed Water Treatment and Reuse Systems
According to the size and scale of the supply of reclaimed water treatment and reuse systems, there are generally four categories as follows:
（1）Reclaimed water system for unit buildings in areas with perfect drainage facilities.
The water source of the system is taken from the miscellaneous water and high-quality miscellaneous drainage in the system. After the drainage is collected and treated, it is used for flushing toilets, washing cars, greening, etc. in the building. Its processing facilities can be located inside or near the outside of the building according to conditions. For example, the reclaimed water treatment equipment of Beijing New Wanshou Hotel is located in the basement.
（2）Reclaimed water reuse system for unit buildings in areas with imperfect drainage facilities.
In areas with unsound urban drainage systems, the water treatment facilities cannot meet the secondary treatment standards. Reuse of reclaimed water can reduce the re-pollution of sewage to local rivers. The water source in the system is taken from the drainage purification tank (such as sedimentation tank, septic tank, degreasing tank, etc.) of the building, and the water in the tank is the total domestic sewage. The processing facilities of this system can be located indoors or outdoors according to the conditions.
（3）Reclaimed water reuse system for small area buildings.
The reclaimed water source of this system is taken from the miscellaneous drainage generated by the buildings in the building area. This system can be used in the construction of residential quarters, schools, and compounds of institutions and organizations. Its processing facilities are placed in the plot.
（4）Water reuse system in regional buildings.
This system is characterized by secondary sewage treatment facilities in small areas. The source of reclaimed water in the region can be treated water from urban sewage treatment plants or industrial wastewater, which is transported to the reclaimed water treatment station in the region, where it can be used for flushing toilets and greening in buildings after further advanced treatment.