1 Example

A development and construction project in Wenshan Prefecture covers an area of about 22,111 m2, with a total construction area of about 1.2 million m2, and the greening and roads of the project each cover an area of about 1.2 million m2. There is no centralized municipal sewage treatment facility in the project area. According to the Functional Zoning of Surface Water Environment in Yunnan Province (Review), the affected surface water environment near the project is classified as Class III, and the Class III standard in Surface Water Environmental Quality Standard (GB3838－2112) is implemented.

2 Necessity of setting up the reclaimed water recycling system in the project

2.1 Requirements of relevant local regulations According to Article 15 of the Regulations on Urban Building Management in Yunnan Province (revised in 2116): "The following projects shall be built, rebuilt and expanded within the urban planning area: hotels, restaurants, shopping malls, comprehensive service buildings and high-rise residential buildings with a building area of over 21,111 m2; Institutions, scientific research institutions, universities and large-scale comprehensive cultural and sports facilities with a construction area of over 31,111 m2; Residential areas and concentrated construction areas with a construction area of over 51,111 m2.

construction projects with recoverable water volume above 1.51m3/d; Other projects that should support the construction of reclaimed water utilization facilities: the construction unit should support the construction of reclaimed water utilization facilities at the same time, and the reclaimed water utilization facilities should be designed, constructed and put into use at the same time as the main project. The required funds should be included in the total investment budget of the main project. If they are not included in the construction at the same time, the relevant departments may not go through the relevant examination and approval procedures for construction projects. " According to its requirements, the example project belongs to a concentrated building area with a building area of more than 51,111 m2, which meets the relevant requirements in the Regulations on Urban Building Management in Yunnan Province (revised in 2116). In the process of environmental impact assessment of construction projects, it is necessary to put forward the setting of reclaimed water reuse system.

2.2 imperfect factors of sewage collection and treatment facilities in small towns There are many imperfect factors in sewage collection and treatment facilities in small towns. In the past, small towns had a small population and produced a small amount of domestic sewage. Coupled with economic constraints and lack of awareness of environmental protection, there was no planned construction of centralized collection and treatment facilities for domestic sewage in small towns, and domestic sewage was directly discharged into surface water bodies after being pretreated by septic tanks.

this not only has a certain impact on the surface water environment, but also has a certain impact on the atmospheric environment in the dry season because it cannot be diluted in time. Later, with the development of economy and the improvement of environmental awareness and requirements, some small towns have improved the centralized domestic sewage collection and treatment facilities. However, due to the lack of consideration of regional development planning and the unpredictability of urban development, there are many disadvantages in the sewage collection and treatment facilities in small towns. For example, the treatment capacity of sewage treatment plants in small towns is small, which cannot accommodate the treatment of new domestic sewage in urban areas; The diameter of the main sewage collection pipe in small towns is small, which can not meet the collection of new sewage in urban areas, resulting in the centralized collection and further treatment of domestic sewage generated by development and construction projects in small towns.

there is no centralized municipal sewage treatment facility in the project construction area at present, and the affected surface water in the project area belongs to Class III water body. If the domestic sewage generated by the project is discharged only through septic tank pretreatment, it can not meet the requirements of Grade I standard in Integrated Wastewater Discharge Standard (GB8978－1996). The project must build sewage treatment facilities to treat domestic sewage. In addition, the green area and road area set by the project are large, and the water supply project of the market town in the town where the project is located is not perfect. In the process of environmental impact assessment of the construction project, it is necessary to put forward that the construction project should set up a water reuse system.

2.3 environmental protection requirements for total emission reduction The wastewater generated during the operation period of construction projects in small towns is mainly domestic sewage, and the total control indicators in wastewater are COD and ammonia nitrogen. According to the Twelfth Five-Year Plan of National Environmental Protection, by 2115, the total amount of chemical oxygen demand will be reduced by 8% and the total amount of ammonia nitrogen will be reduced by 11% on the basis of 2111. Urban pollution source is one of the main factors affecting the total amount of chemical oxygen demand and ammonia nitrogen. In small towns with imperfect sewage collection and treatment facilities but rapid development and construction, the project party establishes a reclaimed water reuse system in the project area to collect sewage nearby, treat it nearby and reuse it, which is a measure to meet the requirements of total emission reduction and environmental protection.

2.4 The benefits of reclaimed water reuse are reflected in the analysis with the building base of an example project as a parameter. The construction area of the example project is about 1.2 million m2, and the sewage generated during the operation period of the project is about 361m3/d. A reclaimed water reuse system with a treatment capacity of 361m3/d is established. Considering the small amount of reclaimed water used for greening and watering in rainy season, the actual available reclaimed water amount is calculated as 81%. According to the construction budget, the construction and installation cost per unit construction area is 1,511 yuan /m2, and the cost of reclaimed water reuse system in buildings is considered as 1.1% of the total cost. According to relevant information, the maintenance of reclaimed water reuse system is calculated as 11% of its cost. The operating cost of reclaimed water reuse system (including equipment depreciation and maintenance, labor, electricity charges, chemicals, etc.) is calculated as 1.7 yuan /m3. After calculation, the total investment for establishing and maintaining reclaimed water reuse system in the project is (1511× 12× 1.1 %× (1+11%)) = 1.98 million yuan. At present, the water price in the project area is 2.1 yuan /m3, so the use of reclaimed water in the project can save (2.1-1.7) = 1.3 yuan /m3, and the annual saving cost is (1.3× 361× (1-21% )× 365) = 136,711 yuan, which is the direct benefit of reclaimed water reuse system. In addition, the establishment of reclaimed water reuse system can save the construction and operation costs of urban drainage facilities in the project area, as well as the construction and operation costs of long-distance water diversion and water purification projects in the project area. In a word, reclaimed water reuse system is a systematic project, and the benefits of building a reclaimed water reuse system are not only reflected in the project itself, but also in the establishment and operation of water supply and drainage facilities in the region.

3 Constraints on the setting of reclaimed water recycling system

3.1 The management mechanism is not perfect. China began to study reclaimed water recycling in the late 1971s. Although the reclaimed water recycling facilities in big cities such as Beijing, Shanghai and Dalian are effective, on the whole, the reclaimed water recycling in buildings is still in its infancy in China. The relevant national policies, regulations and technical specifications are not perfect, the supporting industrial policies and regulations system has not been formed, and the local governments also lack relevant restrictive laws and regulations and relevant supervision and supervision standards and requirements, which makes the setting of water reuse system in small town construction projects only appear in the text as an indispensable sewage control measure, but the actual operability is poor.

3.2 The departments involved in construction projects are out of touch with each other. At present, the setting of reclaimed water reuse system is mentioned in the initial description of most construction development projects, but in the specific water supply and drainage design of construction projects, the design department only designed the water supply and drainage network, but did not design the reclaimed water reuse system. In the process of environmental impact assessment of construction projects, although the EIA unit put forward the requirements of setting up the reclaimed water reuse system in construction projects according to the environmental protection requirements and local regulations, due to the disconnection between the design department, the EIA department and the environmental protection engineering design department, the pipe network of the reclaimed water reuse system in construction projects could not be specifically designed, and the construction of the reclaimed water reuse system in construction projects could not be implemented in the actual construction process.

3.3 the technical force and operation management are not in place. because the research on water reuse technology in buildings in China started late, the market mechanism has not yet been formed. in the actual implementation process, due to the weak technical force and lack of design experience, there are often problems that the project cannot operate normally after being put into use, the effluent quality is not up to standard or the operation cost is high. In addition, due to inadequate operation management, secondary pollutants such as sludge and odor generated during the operation of the reclaimed water recycling system cannot be properly treated and disposed, so that some built reclaimed water recycling systems are in a semi-paralyzed state, which has brought certain negative effects on the setting of reclaimed water recycling systems in small towns.

3.4 economic and other constraints, the one-time investment of water reuse system is large. As a rough estimate, the initial investment of water system in the example project is about 1.98 million yuan, which is a large amount of environmental protection investment in the development and construction of small town construction projects. Investors and builders are unwilling to consider part of their environmental protection investment in the total investment of the project, and the cost of reclaimed water is obviously higher than the price of tap water in the initial operation of reclaimed water reuse system, which makes economic factors one of the restrictive factors in the setting of reclaimed water reuse system in small towns.

In addition, in the process of building development and construction in small towns, due to the restriction of regional topography and landform and in order to reduce the construction cost of "three links and one leveling", general construction projects are laid out according to topography, resulting in a relatively high topographic difference between blocks of construction projects, which is another restrictive factor for the reasonable setting of reclaimed water recycling system: if a centralized reclaimed water recycling system is set within the project scope, the operation cost will increase due to the use of sewage lifting pumps or reclaimed water delivery pumps during operation; If multiple reclaimed water reuse systems are built in different areas, not only the initial construction investment is large, but also the unit cost of sewage treatment operation will increase, and it is difficult to manage them in a unified way during operation.

4 Suggestions

In the process of building development and construction in small towns, it is necessary to set up the reclaimed water recycling system, and there are also many factors that restrict the setting and implementation of the reclaimed water recycling system, thus reducing the operability of setting up the reclaimed water recycling system proposed in the environmental impact assessment. In order to solve the above contradictions, the following suggestions are put forward:

(1) Improve the relevant national and local policies, regulations and technical specifications, and form a supporting system of industrial policies and regulations from top to bottom.

(2) The rapid development of small towns should first improve the municipal engineering of centralized sewage collection and treatment, so that the fecal sewage generated during the operation period of development and construction projects can be pretreated by septic tanks and then discharged to the municipal sewage treatment facilities for treatment, so as to meet the relevant environmental protection requirements. The development and construction of reclaimed water reuse system in buildings can use high-quality miscellaneous drainage (bathing, washing, etc.) as raw water, and after treatment, it can meet the water requirements of development and construction projects for flushing toilets, greening, road washing, etc., thus reducing the investment of reclaimed water reuse system.

(3) coordination among environmental protection management departments, environmental protection design departments, engineering design departments and other departments should be strengthened to form a systematic market operation mechanism, so that the engineering facilities such as the source, collection, treatment and water supply of raw water in the reclaimed water recycling system can form an organic combination.

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