1 reused after secondary treatment category project unit price unit of measurement Total (ten thousand yuan) Accumulated (ten thousand yuan) Pipe Network Indoor and outdoor water 18 yuan / m 2 100 000m 2 180 360 Indoor and outdoor drainage 18 yuan / m 2 100 000m 2 180 equipment Processing equipment (including control) 20,000 yuan 28 30 Pressurized equipment (including control) 20,000 yuan 2 Structure Regulation pool 1 000 yuan / m 3 60m 3 6 20 Middle pool 1 000 yuan / m 3 40m 3 4 equipment room 1 000 yuan / m 2 100m 2 10 Total investment (ten thousand yuan) 410 Increase investment (yuan/m2) 41 Note: 1 pipe network refers to the added pipe system; 2 the area in the table refers to the building area. 2 reused after three levels of processing 2.1 Features category project unit price unit of measurement Total (ten thousand yuan) Accumulated (ten thousand yuan) Pipe Network Indoor and outdoor water 18 yuan / m 2 100 000m 2 180 180 equipment Processing equipment (including control) 420,000 yuan 42 44 Pressurized equipment (including control) 20,000 yuan 2 Structure Regulation pool 1 000 yuan / m 3 60m 3 6 26 Middle pool 1 000 yuan / m 3 40m 3 4 equipment room 1 000 yuan / m 2 160m 2 16 Total investment (ten thousand yuan) 250 Increase investment (yuan/m 2 ) 25 Note: 1 pipe network refers to the added pipe system; 2 the area in the table refers to the building area. 3 Reuse after MBR processing 3.1 Features are characterized by: category project unit price unit of measurement Total (ten thousand yuan) Accumulated (ten thousand yuan) Pipe Network Indoor and outdoor water 18 yuan / m 2 100 000m 2 180 180 equipment Processing equipment (including control) 74 million yuan 74 76 Pressurized equipment (including control) 20,000 yuan 2 Structure Regulation pool 1 000 yuan / m 3 70m3 7 19 Middle pool 1 000 yuan / m 3 45m3 4.5 equipment room 1 000 yuan / m 2 75m 2 7.5 Total investment (ten thousand yuan) 275 Increase investment (yuan/m 2 ) 27.5 Pipe network depreciation fee Equipment depreciation Processing fee Electricity fee Labor and other total 0.69 0.59 1.05 0.20 0.14 2.67 4 Conclusion Through the comparison of the initial investment and operating costs of the three treatment methods, it can be seen that the traditional sewage treatment and reuse method (feces, sewage diversion) has lower equipment and processing costs, but the network cost of divertible drainage is increased. The initial investment is greatly improved, and the resulting high operating depreciation cost completely loses the advantage of low processing cost of the process, and thus is not suitable for use in water treatment in residential areas. 
Due to the different water sources and treatment methods, the water system can take many forms, and the choice of which form is the key to the design. Taking a certain district as an example, three typical treatment methods are selected to analyze and compare the water balance, initial investment and operating costs. The whole plot is a 6-storey brick-and-concrete residential building with a total construction area of ​​10×10 4 m 2 and a plot ratio. At 1.2, the green area is 30%, with 1,100 households, 3,300 people, and 270 vehicles).
1.1 Features are characterized by:
a. It is a traditional treatment form, with mature technology, small sludge production and less equipment investment;
b. Using domestic sewage (excluding feces) as the water source, it is required to implement sewage and sewage diversion;
c. The time and season flow of the raw water vary greatly, and the water balance is difficult;
d. The effluent water quality can only meet the requirements of flushing and greening.
1.2 Water balance
Water balance is the key to the design of the water system. It is not only the basic basis for determining the processing capacity of the equipment, but also a reliable guarantee for the operation of the water system. It is also a prerequisite for reducing the operating cost of the water. The water balance of the first reuse scheme is adopted.
1.3 Equipment technical parameters Through the analysis of water balance, the technical parameters of the equipment are determined as follows:
Design processing capacity Q set = 150m 3 / d
Adjustment tank volume V adjustment = 0.4Q set = 60m 3 ;
Medium pool volume V = 0.25Q set = 38m 3 (design value 40m 3 );
The water supply pump Q pump = 25Q / 24 = 14.3 m 3 / h; H = 392 ~ 441 kPa, N = 4 kW.
1.4 Economic Analysis
The initial investment in the project refers to the increased cost of using the water reuse system compared to the non-use, the same below.
The initial investment calculation results of the first scheme are shown in Table 1, and the operating cost analysis is shown in Table 2. Pipe network depreciation fee Equipment depreciation Processing fee Electricity fee Labor and other total 1.44 0.24 0.7 0.20 0.24 2.82
Its characteristics are:
a. It is a traditional treatment form, with mature technology, large sludge production and high equipment investment;
b. Using domestic sewage (including feces) as a water source, without the need for manure and sewage diversion, reducing the initial investment of the pipe network;
c. The change of the time and season flow of the raw water is small, and the water source is sufficient;
d. The effluent water quality can only meet the requirements of flushing and greening.
2.2 Water balance The water balance of the second scheme.
2.3 Equipment technical parameters
The technical parameters of the equipment are the same as 1.3.
2.4 Economic Analysis
The initial investment calculation results of the second scheme are shown in Table 3, and the operating cost analysis is shown in Table 4. Pipe network depreciation fee Equipment depreciation Processing fee Electricity fee Labor and other total 0.72 0.35 1.0 0.20 0.36 2.63
a. It is a new type of treatment process, the sludge output is very small and PLC automatic control is adopted, which is convenient to operate but has a large investment in equipment;
b. The renewal of the membrane will increase the operating cost;
c. Using domestic sewage (including feces) as a water source, without the need for manure and sewage diversion, reducing the initial investment of the pipe network;
d. The change of the time and season flow of raw water is small, and the water source is sufficient;  e. The effluent water quality is good, in addition to meeting the requirements of flushing and greening, it can also be used for car washing.
3.2 Water balance
Water balance of the third scheme
3.3 Equipment technical parameters design and processing capacity Q set = 180m 3 / d;
Adjustment tank volume V adjustment = 72m 3 (design value is 70m3);
The tank volume V = 45m 3; 
The water pump Q pump = 2.5Q medium / 24 = 14.8 m 3 / h; H = 392 ~ 441 kPa, N = 4 kW.
3.4 Economic Analysis The initial investment calculation and operating cost analysis using the third option are shown in Tables 5 and 6, respectively. Note: 1 pipe network refers to the added pipe system; 2 the area in the table refers to the building area.
The same is the treatment of domestic sewage, although the traditional three-stage treatment method is lower than the initial investment and operating cost of the MBR method, but the advantage is not obvious, and the high-quality water provided by MBR is more acceptable from the user's mind, and can Extend the service life of water supply equipment, pipe network and appliances, and the economic benefits of high-quality water used for car washing can not be ignored. With the development of membrane production technology and the reduction of the price of membrane modules, the investment cost and operating cost of MBR will also decrease, which has been confirmed in Japan. Therefore, from the perspective of development, the MBR method, which occupies a small area, does not pollute the environment, is highly self-controlled, and operates reliably, should be the first choice for water reuse in residential areas.
Water treatment system plan and economic comparison in residential areas
From: "China Water Supply and Drainage" Mo Hui, Liu Jianhua, Zhong Xinhua, Hu Weiqing
At present, the conditions for the construction of the water system in the residential area are basically in place and are becoming more and more perfect. First of all, the residential area has a large displacement, large demand for miscellaneous water, and easy water balance, which is beneficial to the design and smooth operation of the water system. Secondly, with the scale of urban residential communities and the development of water treatment technology, the beginning of the water system Investment and operating expenses will be greatly reduced; once again, the privatization of housing, the rise and improvement of residential property management also laid the foundation for the return on investment of the water system. After adopting the water system, it is estimated that the water consumption in the residential area can be saved by 30% to 40%, and the displacement can be reduced by 35% to 50%, which will produce good social and environmental benefits.
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