GB/T 19570-2004 Technical specification for sewage discharge pipeline engineering
Some standard content:
ICS 13.060.30
National Standard of the People's Republic of China
GB/T19570—2004
Engineering technical specification for sewage pipeline discharging into the sea
Issued on 2004-07-26
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Standardization Administration of China
Implemented on 2005-01-01
Appendix A of this standard is an informative appendix.
This standard is proposed by the State Oceanic Administration
This standard is under the jurisdiction of the State Oceanic Standard Planning Center. Foreword
The drafting unit of this standard is the First Institute of Oceanography of the State Oceanic Administration. The main drafters of this standard: Xu Jiasheng, Liu Changrong, Meng Yi, Song Wangde, Bo Zengdi, Zhang Xiaolong GB/T19570—2004
GB/T19570—2004
Sewage discharge pipelines to the sea are an important part of sewage treatment projects in coastal cities. In order to improve the sewage treatment capacity of coastal cities, protect marine resources and environment, promote the sustainable development of marine economy, and reduce the pollution of sewage to the ocean, this standard is specially formulated based on the current status of domestic and foreign sewage discharge pipeline engineering technology development.
This standard strives to fully reflect the connotation and essence of sewage discharge pipeline engineering technology, while effectively guiding the important links of sewage discharge pipeline engineering technology, such as route survey, sewage discharge mixing area adjustment, sewage pollution control to the marine environment, pipeline design, construction, etc., so as to promote the continuous improvement of sewage discharge pipeline engineering technology in my country and the continuous improvement of marine environmental protection level. #Scope
Technical Specification for Sewage Pipeline Engineering
GB/T 19570--2004
This standard specifies the technical requirements for route survey and selection, sewage mixing zone, pipeline design and construction of sewage pipeline engineering.
This standard is applicable to sewage (excluding warm water) pipeline engineering in the sea area under the jurisdiction of the People's Republic of China. 2 Normative References
The clauses in the following documents become the clauses of this standard through reference in this standard. For all dated referenced documents, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, the parties who reach an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used: For all undated referenced documents, the latest versions are applicable to this standard. GB3097 Seawater quality standard
GB/T12763.2 Marine survey specification Marine hydrological observation GB/T12763.3 Marine survey specification Marine meteorological observation GB/T12763.6 Marine forest survey specification Marine biological survey GB/T32763.8 Marine survey specification Marine topography and geophysical survey GB/T14914 Coastal observation specification
GB17378.4 Marine blue measurement specification
Seawater analysis
GR17378.5 Marine monitoring specification Sediment analysis Marine monitoring specification Organism analysis
GB 17378.6
GBI7501 Marine topographic survey specification
GR 17502
Submarine cable and pipeline route inspection specification
Marine biological quality
GB 18421
GB 18486
Pollution Control Standard for Sewage Treatment Projects in the Sea 3 Terms and Definitions
The following terms and definitions apply to this standard. 3.1
route survey
Route survey
Investigation of the route (pipeline direction) of the submarine pipeline from the starting point to the end point, the marine environment and the status of marine development activities. 3.2
Sewage pipeline discharging into the sea A pipeline laid in the sea for discharging sewage, which consists of a diverter and a diffuser. 3.3
Pipe to outfall
A pipeline that transports sewage from the onshore sewage treatment facility to the diffuser through a surge tank. Note: Modified CB18486-2001, definition 3.2.3.4
Diffusers plpe for diffusers
Pipelines for dispersed sewage discharge in the sea
Note: Rewrite CB18486-2001, definition 3.1 GB/T19570-2004
Sewage mixing area Initlat dllutlon area for sewage discharging fnto the sea The water area formed by the direct mixing of sewage discharged from the diffuser and seawater. It is closest to the sewage discharge point and its range includes the sea area from the seabed to the sea surface, and its water quality has not reached the specified water quality target at any moment. Note: Rewrite GR18486200t, definition 3,5.3. 6
Pipeline laying plpe installation
The sewage pipeline to the sea shall be laid on the seabed surface or buried in the seabed along the route. 4 General Principles
4.1 The sewage pipeline to the sea project shall be demonstrated comprehensively and scientifically to meet the requirements of protecting the marine environment, advanced technology, economic rationality, safety and reliability.
4.2 The sewage pipeline to the sea project design shall adhere to the principle of "determining the land by the sea", that is, to implement the total amount of sewage discharge control. The sewage discharge to the sea mixing area shall be determined according to the hydrodynamic state of the sewage discharge sea and the self-purification capacity of the seawater. The sewage discharge shall always be within the sewage discharge to the sea mixing area. The sewage discharge pipeline project to the sea is not allowed in special marine protection areas, marine nature reserves, important industrial water cities, sea scenic spots and other rare species that need special protection, coral reefs, mangroves, seagrass beds and other important ecological and environmental areas. 4.4 The sewage discharge channel to the sea is not allowed to discharge harmful and toxic sewage. The concentration limit of water pollutants entering the drainage pipe shall be implemented in accordance with the relevant provisions of GB18486. Industrial wastewater and domestic sewage shall be treated at least at the sewage treatment plant level before being discharged into the sea. 5 Route survey and selection
5. 1 Route Survey
5.1.1 Before constructing the sewage discharge pipeline project, the marine environment and marine development activities in the route area should be investigated. 5.1.2 The scope of the sewage discharge pipeline route survey should include the area passed by the discharge pipe and the diffuser. The starting point of the route is the pressure regulating well set at the starting end of the discharge pipe, and the end point is the end of the diffuser. The scope of waves, currents, geological structures and ground development should be expanded to the sea area near the route area.
5.1.3 First, two or more (including) routes are proposed through data analysis and on-site investigation, and the data of the proposed routes are analyzed. Compare and select the appropriate sewage discharge pipeline survey route. 5.1.4 Route survey All items that need to be positioned should use DGPS, and the maximum allowable error of dynamic positioning should not exceed ±3.0m. The maximum allowable error of static positioning should not exceed ±1.0m. During measurement, the projection, coordinates and leveling points and coordinate points near the landing section should also be determined. Positioning is carried out in accordance with the relevant provisions in GB 17501. For other road and mountain survey items and contents, see 5.1.4.1 to 5.1.4.10. 5.1.4.1 Land part survey
The scope of this survey is the land part of the route below the low tide line of the manhole (pressure regulator). The topography should be measured, and the landform and bottom survey should be carried out at the same time. The measurement requirements shall be implemented in accordance with the relevant provisions of GB17501. 5.1.4.2 Meteorological and hydrological survey
This survey should be carried out in representative months, and the data collected should last for at least 1 year. If there is a lack of historical data, it should be obtained through short-term on-site observations that meet the needs of the project and related analysis with nearby long-term observation stations. This survey should include the following contents:
5. 1. 4. 2. 1 Meteorology
This survey should include the following contents:
a) Wind description and direction: The data should be obtained from the meteorological stations near the proposed road and mountain area, and statistical analysis should be carried out. There should be data on the frequency and extreme values of strong winds.
b) Sea fog: average fog opening in each month over many years.
c) Temperature: average temperature and extreme value in each month over many years. d) Meteorological observation method shall be carried out in accordance with the relevant provisions of GR/T12763.3 5. 1. 4. 2.2 Ocean current
This survey should include the following contents:
GB/T 19570—2004
&) Collect data, measure the velocity and direction of the surface and bottom layers and analyze them, calculate the velocity and direction of the residual flow, and the data collected should meet the calculation of the influence of ocean current on pipeline stability.
Ocean current observation should be carried out once for 25 hours during the high tide period and the low tide period, and analysis and calculation should be carried out. c) Ocean current observation should be carried out in accordance with the relevant provisions of GB/T2763,2. 5. 1. 4. 2. 3 Tide
This survey should include the following contents:
a) If there is a permanent tide station in the proposed route area, the tidal data observed over a long period of time should be directly used. b) If there is no annual tide station, a short-term observation for one month should be carried out in the proposed route area, and then the data from the nearby tide stations should be correlated and analyzed, and the design tide level should be calculated. The design tide level should take into account the impact of storm surge. c) Tide level observation shall be carried out in accordance with the relevant provisions of GB/T11914. 5.1.4.2.4 Waves
This monthly survey should include the following contents:
a) If there is a permanent wave observation station in the proposed route area, the wave data of the station shall be used directly. Otherwise, a temporary wave observation station shall be set up in the proposed route area to carry out wave observations for no less than three consecutive human wave periods in a year. b) The wave observation content of the temporary wave observation station includes wave quotient, wave direction, period, wave type and sea state, and the observation data of the nearby permanent wave station shall be correlated and analyzed, and the 50-year wave element shall be taken as the design parameters of the discharge pipe and diffuser. ) Wave observation shall be carried out in accordance with the relevant provisions of GB/T12763.2. 5. 1.4.2.5 Water temperature and salinity
The survey of this project should include the following:
a) Mainly collect historical data. If data is lacking, the actual measurement work should be carried out in February, May, August and November, and each observation should be carried out for one night. Special attention should be paid to the temperature and salinity layers and their distribution positions in the water body. h) Collect water temperature statistical data to determine the design temperature and the temperature strain, deformation and displacement of the pipeline generated by the batch. e) Water temperature and salinity observations shall be carried out in accordance with the relevant provisions of GB/T12763.2. 5. 1. 4. 2. 6 Sea ice
This survey should include the following:
) Determine whether the route area passes through the sea area of fixed ice or drift ice activity; for fixed ice, the ice age time, range, water temperature, ice temperature, air temperature and ice thickness should be observed; for drift ice, the ice size, flow velocity and flow direction should be observed, and the physical and mechanical properties of ice should be calculated. b) Data on historical ice disasters and severe ice periods should be collected: c) Sea ice observations should be carried out in accordance with the relevant provisions of GB/T12763.2. 5.1.4.3 Diffusion coefficient
The horizontal and vertical diffusion coefficients of the surveyed sea area should be obtained using dye method, buoy method or other scientific methods. 5.1.4.4 Engineering geophysical exploration
This survey should include the following:
a) The width of the survey route should not be less than 500m. The scale of the survey map should not be less than 1:2000. The layout of the survey line and the accuracy of the survey should meet the requirements of the map scale.
b) The water depth, seabed topography and shallow stratum profile should be measured simultaneously in the proposed route area. The technical requirements are as follows: 1) In water depth measurement, in sea areas with a water depth greater than 10m, a multi-beam sounding system is used to conduct full coverage water depth measurement of the routing area. In sea areas with a water depth less than 10m, a dual-frequency sounder is used for water depth measurement. The measurement is carried out in accordance with the relevant regulations in GB17501.
For bottom landform detection, a side-scan sonar is used to conduct full coverage measurement of the routing area. The single-side scanning range should not be greater than 75m. 23
Obstacles such as bedrock outcrops, large boulders and gravel, sand waves, sunken ships, submarine pipelines and other artificial facilities on the seabed should be clearly indicated, and the interpretation of detection data shall be carried out in accordance with the relevant regulations in GB/T12763.8. 3) Shallow stratum profile measurement, use shallow stratum profile meter to conduct stratum detection, the detection depth of loose sediments should be no less than 25m, the resolution should reach 0.3m, and the shallow stratum profile data should be interpreted. The measurement shall be carried out in accordance with the relevant provisions of GB17502. Magnetometer measurement, use magnetometer to detect ferromagnetic objects in seabed sediments, and mark the positions of installed optical cables, pipes, anti-ships and explosives. The measurement shall be carried out in accordance with the relevant provisions of GB17502. 5) The water depth, landform and shallow stratum profile data obtained by synchronous measurement shall be made into an integrated and corresponding histogram. 5.1.4.5 Engineering Geology
This survey shall include the following contents:
a) The specific requirements for the layout of sampling points shall be carried out in accordance with the relevant provisions of GB/T12763.8. Use Korean, Chinese and columnar samplers to collect surface samples and columnar samples, use CPT (static penetration tester) to conduct in-situ testing of rock and soil, and provide bottom plug type distribution map and columnar surface map of the survey area. For the bottom type that is prone to liquefaction, its range should be accurately marked. b) The boreholes are arranged according to the survey scale and engineering needs, mainly distributed along the center line of the pipeline. Drilling holes should be arranged at the shore, the end of the discharge pipe and the diffuser, and the rest should be determined according to the situation. The drilling depth should be greater than the buried depth of the pipeline, the minimum drilling depth should be greater than 5m (stop drilling when reaching the bedrock), and the core sampling interval should not be greater than 1.0m + 1.0m. In addition to the mechanical property test of rock and soil samples, source position test (standard penetration, cross plate shear, etc.) should also be carried out according to the characteristics of rock and soil. The technical requirements and report writing of drilling shall be carried out in accordance with the relevant provisions of GB17502.
The samples obtained should be subjected to geotechnical tests with gauges on site or in the laboratory. Finally, the soil is classified and evaluated according to the particle analysis and physical property index of the soil. The content, analysis methods and technical requirements of geotechnical experiments shall be implemented in accordance with the relevant provisions of GB17502.
5.1.4.6 Marine life
This survey shall include the following contents:
a) Phytoplankton (species composition, density, distribution trend, biodiversity index). b) Zooplankton (species composition, density, biomass, distribution trend, biodiversity index). c) Attached organisms (species composition, density, biomass, distribution trend, biodiversity index). d) The surface roughness increase and load changes caused by organisms attached to pipes and diffusers shall be considered, and the structure of the biological community shall be analyzed and the distribution maps of various biological children shall be drawn. e)
f) The calculation of the biodiversity index shall be implemented in accordance with the relevant provisions of GB17378.6. 5.1.4.7 Bottom stability
5.1.4.7.1 Geological structure and earthquake conditions This survey should include the following:
a) Collect or obtain through survey the geological structure and seismic data of the pipeline route area and its nearby sea areas. When the pipeline is located in a degradable area, the possibility of subsoil degrading and sliding caused by seismic activities should be fully considered. The foundation should b) be reinforced to improve the strength of the pipeline.
In sea areas where the seismic intensity reaches the national seismic intensity zone, the pipeline route should be investigated and calculated for its anti-seismic capacity according to the engineering seismic design code.
5. 1, 4.7. 2 Hydrodynamics and scouring and silting This survey should include the following:
a) Understand the characteristics of hydrodynamics on the route area and determine whether it is an scouring or silting area. b) Within the design life of the pipeline system, take the 50-year wave turbulence, possible maximum flow velocity and tidal level that may cause subsoil liquefaction as the design parameters of the pipeline project. GB/T 19570—2004
c) Analyze and calculate the type, movement, scouring and silting volume and rate of the subsoil, correctly determine the scouring and silting effect of hydrodynamics on the pipeline route area and its hazards, and take engineering measures to prevent scouring and silting. 5. 1. 4. 7. 3 Geological disaster status
This survey should include the following:
a) Classify the types of geological disasters, focusing on collapse, landslide, sand wave movement, buried river channel and shallow natural gas. Conduct an analysis of the causes of geological disasters, focusing on the relationship between the seabed topography, soil quality, geological structure, geodynamics, and sediment h)
The fracture, collapse, and landslide areas should be identified and their scale and morphological characteristics should be described. Analysis of wave morphology, stability, and activity trends should be conducted. d)
The discovered buried ancient river channels should be described in morphology and their buried depths should be determined. e)
1) Determine the distribution range of shallow natural gas and its buried depth. 5, 1. 4. 8 Corrosive environment
This survey should include the following:
Wave and flow conditions,The wave height, wave direction, period, flow velocity and flow should be understood. a)
Substrate type: The substrate type and its characteristics should be understood. b)
Water temperature and mud temperature: The water temperature and mud overflow should be measured. c)
d) pH value: The pH value of seawater and bottom water should be measured. Eh value and resistivity: The Eh value and resistivity of seawater and bottom sediment should be measured. E)
Sulfide: The sulfide content of the bottom sediment should be measured. Organic matter: The organic matter content of the bottom sediment should be measured. Aerobic and anaerobic bacteria: The number of aerobic and anaerobic bacteria such as sulfate-reducing bacteria in the bottom sediment should be measured. Sulfate-reducing bacteria detection should be carried out in accordance with the relevant provisions of GB/T12763.6. i) Biofouling: The attached organisms and drilling organisms in the bottom sediment should be identified and their harmfulness should be analyzed. This survey should be carried out in accordance with the relevant provisions of GB/T 12763.6. i) The determination of PH, Eh and organic matter shall be carried out in accordance with the relevant provisions of GH17378.5. k) Corrosion environment evaluation: After completing the above adjustment and analysis, the seabed corrosion environment evaluation shall be carried out based on the obtained data. 5.1.4.9 Marine environmental quality status and evaluation This survey shall include the following:
a) Escherichia coli decay rate (Tyc)
Use one of the methods such as experimental simulation test, field simulation test and field experiment to measure the concentration of Escherichia coli and its decay rate. This test shall be carried out in accordance with the relevant provisions of GB17378.6. b) Monitoring and analysis of water quality and bottom quality
Monitoring and analysis items include: ice temperature, water color, transparency, salinity, pH, chemical oxygen demand (COD), biotrophic bacteria (BOD), chlorophyll a, dissolved oxygen (DO), oil, nitrogen, inorganic phosphorus, active phosphate, organic matter, sulfide, copper (Cu), arsenic (Se), cadmium (Cd), mercury (Hg), zinc (Zn), lead (Pl), total sulfide, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBu) and other pollutants. The above-mentioned surveys should be carried out in accordance with the relevant provisions of (R17378.4 and GB17378.5). c) Environmental quality evaluation
Comprehensive evaluation is carried out through investigation of the environmental quality of the Liuhai area. d) Establishment of control area
A control area should be established outside the sewage discharge area, that is, in the sea area not affected by sewage discharge, and the sewage discharge area and the control area should be investigated and compared to distinguish the changes in environmental quality caused by natural four elements and human pollution. GB/T 19570—2004
5.1.4.10 Utilization of sea areas and marine resources This survey includes the following contents:
a) Survey of aquaculture and fishing activities in the route area. This survey includes aquaculture scope, species, fishing types, quantity, number, tonnage, and distribution of fishing vessels.
b) Survey of ports and shipping conditions near the route area, including the number, tonnage, weight, depth of penetration into the bottom mud, and route location.
Find out the locations of existing submarine pipelines, sunken ships, other artificial facilities, and waste. c
d) Survey and determine the locations of the route area and its surrounding areas, tourist areas, nature reserves, dumping areas, and military training areas. 5.2 Route selection
5.2.1 Analyze and compare the data obtained from the survey of sewage discharge pipelines to the sea, point out the favorable and unfavorable conditions of the route marine environment and development activities, and conduct a comprehensive evaluation. 5.2.2 According to the requirements of marine functional zoning and the principle of environmental protection in the pipeline route area and sustainable development of the adjacent sea areas, the best route shall be determined by comparison in accordance with the scientific, reliable and economic requirements of the pipeline project: 6 Sewage discharge to sea mixed zone
6.1 Prediction of water quality changes
On the basis of the sewage discharge volume and treatment degree determined in the first process, the sewage discharge pipeline route area, the marine functional zone of the adjacent sea area and its water quality requirements shall be reported to predict its water quality changes, and mathematical models shall be used to predict the temporal and spatial distribution of human sewage in the discharge area and its impact on the ecological environment.
6.2 Investigation of mixed zone
The investigation of sewage discharge to sea mixed zone shall be carried out in accordance with the relevant provisions of 5.1.4.2.5.1.4, 4, 5.1.4.6 of this standard. 6.3 Selection of mixed zone
6.3.1 The filtration unit shall be selected according to the marine functional zoning and the self-purification capacity of seawater. 6.3.2 In addition to the marine functional zoning, the selection of mixing zones and discharge points should also take into account the hydrodynamic conditions of the sea area and the geological and geomorphological conditions of the route. The waters with stable seabed, open sea area, active hydrodynamics, water depth greater than 10IM, relatively poor biological resources, simple seabed conditions and easy pipeline construction should be selected.
6.3.3 The mixing zone formed by the discharge of sewage from the discharge point should not affect the migration of fish and the functions of the adjacent functional areas. 6.3.4 The scope of the mixing zone should be determined based on the requirement that the sum of the CO background of the discharged sewage and the receiving water body does not exceed the seawater quality standard specified in GB 3097 (CODa5mR/L), and the scope of the mixing zone shall be implemented in accordance with the relevant provisions of GB18486. 6.3.5 When calculating the scope of the mixing zone, different calculation formulas should be used according to its topography, geomorphology and hydrological characteristics and the structure and non-modified surface of the diffuser.
6.3.6 "The water quality in the mixing zone is allowed to exceed the specified water quality standard, but oil film, unpleasant odor and visible cloudy spots cannot be formed. 6. 4 Water quality target
The water quality standard of the sewage discharge area is for the sea area outside the mixing zone. The water quality change of the sewage receiving area outside the mixing zone should be controlled within the scope of the local "Marine Functional Zoning" regulations. The water quality of the sewage discharge area should meet the requirements of the relevant provisions of GB3097. 6.5 Environmental quality analysis
When conducting environmental quality analysis of the mixed area, the environmental quality analysis results of 5.1.4.9 should be used as the background value. According to the relevant provisions of the marine functional zoning and GB3097, the environmental quality base absorption degree of the mixing zone is analyzed and evaluated, and the basis for the selection of sewage release diffusion multiples is provided.
6. 6 Ecological objectives
In the sea areas outside the mixing zone, the benthic animal community structure should be investigated and analyzed. The main indicators for determining ecological objectives include the number of species, habitat density, biomass and biodiversity index. The change of the above indicators shall not exceed 15% of the background value. 6.7 Biological quality objectives
GB/T 19570—2004
When sewage is discharged into the sea outside the mixing zone, the total content of heavy metals such as mercury, zirconium, copper, zinc and petroleum hydrocarbons in the polluted area of the sea should be lower than the third category standard in GB 18421. 6.8 Calculation of total sewage volume
The total amount of sewage entering the sewage treatment and discharge system should be calculated, including domestic sewage and industrial wastewater. If a sewage and water separation interception system is not established, the mixed sewage should also include some surface runoff water. 6. 9 Physical purification process of sewage
Physical purification process is the main process for sewage purification in the sewage discharge area. In the different stages of sewage mixing and transportation in the sewage discharge area, appropriate prediction models should be adopted, and the initial dilution should be calculated, the migration stage, long-term diffusion, and auxiliary transportation stage should be predicted to determine the possibility of establishing a sewage discharge area.
6.10 Initial dilution
After sewage is discharged from the diffuser, it is diluted at the outlet. The dilution multiple is called the initial dilution. Its calculation should be carried out for the following two situations:
a) When the surrounding seawater density is uniform, it is calculated according to the following formula S1 = s. (1-
S.0.38(g)*hy
In the formula;
S.---initial dilution;
S.…dilution at the axis when there is no water flow; .——surrounding seawater density;
%——sewage density;
-mgravitational acceleration, in meters per square second (m/s\); sewage discharge depth, in meters (rl); mixing volume per unit length of diffuser, in cubic meters per second (m/(s·m)); seawater flow rate, in meters per second (m/s). b) When the surrounding seawater density is linearly distributed, it is calculated according to the following formula: 25.
S - 0. 31(g)tz4
S.Axis dilution when the pollution cloud rises to the maximum height in still water zm--maximum buoyancy height of the pollution cloud, in meters (m). zux = 6.25(gg)
Lg(pp)
Other symbols have the same meaning as formula a) in 6.9: 6.11 Key data for initial dilution design
One is to determine the initial dilution required for the project (Sreg), and the other is to determine the submergence state of the sewage field (Hreq). Different sea areas and projects have different requirements for Srcg and Hreq. Sreq and Hreq should be determined according to the requirements of 6.J16.12 Determination of initial dilution (Sreq) and submergence depth (Hreg) The determination of initial dilution and submergence depth shall be in accordance with the following criteria: GB/T19570-2004
It shall ensure that the water around the sewage discharge area meets the predetermined water quality standard; a)
b) To avoid the formation of a stable surface sewage field, Sreq shall be greater than 100 times; c) Sreq shall ensure that the water bacteria in the mixing area do not form an oil film with obvious mixed spots and no unpleasant odor; d) Prevent the sewage field from submerging in the deep water layer and the shallow layer to form a very thin sewage field. 6. 13 Re-dilution of the polluted plume
The frequency and duration of the intrusion of sewage concentration in the waters around the sewage discharge mixing area and the protection area shall be calculated to evaluate the intrusion and harm of the polluted plume to the surrounding waters. 6.14 Calculation formula for re-dilution of pollutant streams When the pollutant concentration in the nearshore area calculated according to the initial dilution plus the background concentration of the receiving water exceeds the seawater quality standard specified in the "Marine Functional Zoning", a sewage re-dilution and migration stage prediction model should be established according to the water quality requirements of the local marine functional zoning to calculate the subsequent transport and diffusion. The calculation uses the Braoks formula, and other models can also be used for calculation. The calculation and application conditions of the commonly used Brooks formula refer to Appendix A.
6.15 Pollution plume concentration field prediction model
When the pollution plume disappears and a smoothly changing concentration field appears, a concentration field prediction model for the influence of pollutant balance should be established outside the sewage-sea mixing zone to calculate the time and impact range required for the pollutants in the seawater to reach the water quality requirements specified in the "Marine Functional Zoning" after dilution.
6.16 Migration of pollutants
The migration law of pollutants in the sea area should be mastered through the Lagrangian drift and Lagrangian residual flow of water particles, and the location of sewage discharge points should be selected based on this, and the possibility of pollutant migration causing harm to the nearshore or marine nature reserves should be evaluated. 6.17 Wind-driven currents and movement of sewage fields
The velocity and direction of wind-driven currents should be calculated to understand the movement speed and direction of sewage fields on the water surface. 6.18 Investigation of solid particles in sewage
When the amount of suspended and deposited solid particles caused by sewage discharge is greater than 10% of the amount of suspended and deposited solid particles in the ocean, the sedimentation status of solid particles in sewage on the seabed should be investigated and predicted. This investigation should be carried out in accordance with the relevant provisions of GB17378.5. 7 Drain pipes and diffusers
7.1 General
Drain pipes and diffusers are important components of sewage discharge pipelines. In addition to natural conditions, their design should also take into account the current social and economic situation, development needs and their impact on the marine environment. Various factors affecting their safety and efficiency should also be fully and comprehensively considered.
7.2 Design requirements
7.2.1 The discharge volume of urban sewage should be designed in the short term and long term according to urban planning. The calculation period for the short-term sewage discharge fan is 10 years, and the calculation period for the long-term sewage discharge volume is at least 20 years. On the basis of the above planning, determine the scale of the sewage discharge project and the diameter of the sewage pipe. The construction of the project can be carried out in stages. The sewage discharge capacity of the sea discharge pipe should be designed according to the long-term sewage angle, and intermittent discharge should be adopted to achieve the self-purification flow rate.
7.2.2 A comparative analysis of the construction costs of sewage treatment plants and sewage pipelines for sea discharge should be conducted. The economic bearing capacity and social and economic benefits of constructing sewage pipelines should be fully considered. 7.2.3 A sewage and rainwater separation interception and treatment system should be established to reduce the burden of sea discharge pipelines and save money. 7.2.4 In the design of pipeline systems, the design internal pressure is used as the basis for calculating the maximum internal pressure. It should be able to withstand the maximum possible external pressure. The design temperature range of the pipeline is -20℃～tu℃.
7.2.5 The normal use and installation design states should be considered separately, and the pipeline system should be designed for these two states according to the load conditions. The design should ensure the function of the pipeline system under the design conditions and prevent possible structural failure or damage. 7.2.6 The structural analysis model of the pipeline system should be able to accurately simulate the main characteristics of the real structural system, including loads, support conditions and structural GB/T19570—2004
characteristics. The mechanical calculation of the pipe system should be carried out according to the requirements of statics, dynamics, material strength theory, fracture mechanics and damage mechanics. 7.2.7 The strength, stability and fatigue safety indexes of all pipe accessories under working load and environmental load should not be lower than those required by the pipe.
7.2.8 The material for manufacturing the sewage pipe should be selected according to the characteristics of sewage, service life, water temperature, freezing conditions, pipe diameter, pressure inside and outside the pipe, soil quality, hydrodynamic conditions, erosion and engineering costs. 7.2.9 If the sewage pipe needs to turn, its corner should be greater than 120°. 7.2.10 The buried depth of the sewage sea pipe should be calculated according to the number and tonnage of ships passing by in the buried area, the size and weight of the pipe, the outer diameter and wall thickness of the pipe, and the scouring effect of the tide and current on the seabed. 7.2.11 According to the laying form of the pipeline, that is, surface laying or seabed burial, an appropriate diffuser should be used. 7.2.12 When calculating the length of the discharge pipe, the discharge pipe should be perpendicular to the flow direction of the ocean current, and the water depth at the end of the discharge arm should be greater than 10. III It should be ensured that the edge of the plume generated when the sewage discharged from the first hole of the diffuser reaches the water surface does not touch the coast. 7.2.13 The length and orifice design of the diffuser should meet the specified initial dilution multiple requirements (about 100 times), and the characteristic parameter of the diffuser dilution function should not be less than 150 times.
7.2.14 The length of the diffuser is closely related to the dilution effect. The length of the diffuser is expressed by the following formula: Lb = 4.27Q5h -2/g172
Where:
la——diffuser length, in meters (m); Q--sewage discharge, in cubic meters per second (t/s); π--the maximum buoyancy height of sewage, in meters (m); &--reduced gravity acceleration, in meters per square second (m/s); S. Initial dilution.
-+( b )
7. 2. 15 The flow velocity in the diffuser should reach the self-purification velocity, that is, not less than 0. 6 m/s, generally 0. 8 m/s~1. 0 m/s or so. The diffuser laid on the seabed should be equipped with a flap gate at the end, which is closed at ordinary times and opened when flushing. 7.2.16 The diffuser should be composed of several pipes with decreasing diameters to maintain the self-purification velocity of the diffuser. 7.2.17 The spacing of the diffuser nozzles is approximately equal to 1/3 of the depth from the nozzle to the water surface. The nozzle spacing should be less than the diffuser length to meet the requirement that the sewage discharged from each nozzle does not overlap each other during the initial dilution and diffusion process. The calculation formula for the number of nozzles is as follows: 31-u
武中:
Lp--diffuser effective length, in meters (m);-...sewage discharge depth, in meters (m). +-+-*++--( ? )
7.2.18 The determination of the nozzle aperture should meet the requirements of sewage dilution and diffusion, and ensure that large-sized suspended matter in sewage can pass smoothly. In the area where sediment accumulates rapidly, there should be a sprinkler to prevent sediment from blocking the diffuser mouth. The nozzle outflow should have a sufficiently large rate. When designing, the Fossil number Fr>1.0, and the nozzle aperture should be 5cm~23cm. The aperture of the nozzle on the i-th diffuser is calculated as follows: cf
rCpV2gE
The outflow velocity of sewage at the nozzle on the first diffuser: Ua = Cp V2gE:
—Flow rate of the i-th hole H:
Cp——Outflow coefficient of the nozzle on the first pipe; g Gravitational acceleration, in meters per square second (m/): F, the eddy diffusion coefficient at the discharge port (X-i). (8)15 Pollution plume concentration field prediction model
When the pollution plume disappears and a smoothly changing concentration field appears, a concentration field prediction model of pollutant balance influence should be established outside the sewage-sea mixing zone to calculate the time and impact range required for pollutants in seawater to reach the water quality requirements specified in the "Marine Functional Zoning" after dilution.
6.16 Migration of pollutants
The migration law of pollutants in the sea area should be mastered through the Lagrangian drift and Lagrangian residual flow of water particles, and the location of sewage discharge mixing zone and discharge point should be selected based on this, and the possibility of pollutant migration causing harm to the nearshore or marine nature reserve should be evaluated. 6.17 Wind-driven current and sewage field movement
The velocity and direction of wind-driven current should be calculated to understand the movement speed and direction of sewage field on the water surface. 6.18 Investigation of solid particles in sewage
When the amount of suspended and deposited solid particles caused by sewage discharge is greater than 10% of the amount of suspended and deposited solid particles in the ocean, the sedimentation of solid particles in sewage on the seabed should be investigated and predicted. This investigation should be carried out in accordance with the relevant provisions of GB17378.5. 7 Drainage pipes and diffusers
7.1 General
Drainage pipes and diffusers are important components of sewage discharge pipelines. In addition to considering natural conditions, their design should also consider the current social and economic situation, development needs and their impact on the marine environment. Various factors affecting their safety and efficiency should also be fully and comprehensively considered. Www.bzxZ.net
7.2 Design requirements
7.2.1 The discharge of urban sewage should be designed in the short term and long term according to urban planning. The calculation period for the short-term sewage discharge fan is 10 years, and the calculation period for the long-term sewage discharge is at least 20 years. On the basis of the above planning, determine the scale of the sewage discharge project and the diameter of the sewage pipe. The construction of the project can be carried out in stages. The sewage discharge capacity of the sea discharge pipe should be designed according to the long-term sewage angle, and intermittent discharge should be adopted to achieve the self-purification flow rate.
7.2.2 A comparative analysis of the construction costs of sewage treatment plants and sewage sea discharge pipelines should be carried out to fully consider the economic bearing capacity and social and economic benefits of the construction of sewage discharge projects. 7.2.3 Establish a sewage and rainwater separation interception and treatment system to reduce the burden of the sea discharge pipeline and save money. 7.2.4 In the design of the pipeline system, the design internal pressure is used as the basis for calculating the maximum internal pressure. It should be able to withstand the maximum possible external pressure. The design temperature range of the pipeline is -20℃～tu℃.
7.2.5 The normal use and installation design states should be considered separately, and the pipeline system should be designed for these two states according to the load conditions. The design should ensure the function of the pipeline system under the design conditions and prevent possible structural failure or damage. 7.2.6 The structural analysis model of the pipeline system should be able to accurately simulate the main features of the real structural system, including loads, support conditions and structural characteristics. The mechanical calculation of the pipeline system should be carried out according to the requirements of statics, dynamics, material strength theory, fracture mechanics and damage mechanics. 7.2.7 The strength, stability and fatigue safety indicators of all pipeline accessories under working loads and environmental loads should not be lower than those required by the pipeline.
7.2.8 The material for manufacturing sewage pipes should be selected based on sewage characteristics, service life, water temperature, freezing conditions, pipe diameter, pressure inside and outside the pipe, soil quality, hydrodynamic conditions, erosion, and engineering costs. 7.2.9 If the sewage discharge needs to turn, its angle should be greater than 120°. 7.2.10 The buried depth of the sewage discharge pipeline to the sea should be calculated according to the number and tonnage of ships passing through the buried area, the size and weight of the pipe, the outer diameter and wall thickness of the pipe, and the scouring effect of the tide and current on the seabed. 7.2.11 According to the pipeline laying form, that is, surface laying or seabed burial, an appropriate diffuser should be used. 7.2.12 When calculating the length of the discharge pipe, the discharge pipe should be perpendicular to the flow direction of the sea current, and the water depth at the end of the discharge arm should be greater than 10°. It should be ensured that the edge of the plume generated when the sewage discharged from the first hole of the diffuser reaches the water surface does not touch the coast. 7.2.13 The length and orifice design of the diffuser should meet the specified initial dilution multiple requirements (about 100 times), and the characteristic parameter of the diffuser dilution function should not be less than 150 times.
7.2.14 The length of the diffuser is closely related to the dilution effect. The length of the diffuser is expressed by the following formula: Lb = 4.27Q5h -2/g172
Wherein:
la——diffuser length, in meters (m); Q--sewage discharge, in cubic meters per second (t/s); π--the maximum buoyancy height of sewage, in meters (m); &--reduced gravity acceleration, in meters per square second (m/s); S. initial dilution.
-+( b )
7.2.15 The flow velocity in the diffuser should reach the self-purification flow velocity, that is, not less than 0.6 m/s, and generally can be taken as about 0.8 m/s~1.0 m/s. The diffuser laid on the seabed layer should be equipped with a flap gate at the end, which is closed at ordinary times and opened when flushing. 7.2.16 The diffuser should be composed of several pipes with decreasing diameters to maintain the self-cleaning flow rate of the diffuser. 7.2.17 The spacing between the diffuser nozzles is approximately equal to 1/3 of the depth from the nozzle to the water surface. The nozzle spacing should be less than the diffuser length to meet the requirement that the sewage discharged from each nozzle does not overlap each other during the initial dilution and diffusion process. The calculation formula for the number of nozzles is as follows: 31-u
Wu Zhong:
Lp--diffuser effective length, in meters (m);-…sewage discharge depth, in meters (m). +-+-*++--(?)
7.2.18 The determination of the nozzle aperture should meet the requirements of sewage dilution and diffusion to ensure that large-sized suspended matter in the sewage can pass smoothly. In areas where sediment accumulates rapidly, there should be a sprinkler to prevent sediment from blocking the diffuser mouth. The outflow rate of the nozzle should be large enough. When designing, the Fr should be greater than 1.0, and the nozzle aperture should be 5cm to 23cm. The aperture of the nozzle on the i-th diffuser is calculated as follows: cf
rCpV2gE
The outflow velocity of sewage at the nozzle on the first diffuser: Ua = Cp V2gE:
—Flow rate of the i-th hole H:
Cp——Outflow coefficient of the nozzle on the first pipe; g Gravitational acceleration, in meters per square second (m/): F, the eddy diffusion coefficient at the discharge port (X-i). (8)15 Pollution plume concentration field prediction model
When the pollution plume disappears and a smoothly changing concentration field appears, a concentration field prediction model of pollutant balance influence should be established outside the sewage-sea mixing zone to calculate the time and impact range required for pollutants in seawater to reach the water quality requirements specified in the "Marine Functional Zoning" after dilution.
6.16 Migration of pollutants
The migration law of pollutants in the sea area should be mastered through the Lagrangian drift and Lagrangian residual flow of water particles, and the location of sewage discharge mixing zone and discharge point should be selected based on this, and the possibility of pollutant migration causing harm to the nearshore or marine nature reserve should be evaluated. 6.17 Wind-driven current and sewage field movement
The velocity and direction of wind-driven current should be calculated to understand the movement speed and direction of sewage field on the water surface. 6.18 Investigation of solid particles in sewage
When the amount of suspended and deposited solid particles caused by sewage discharge is greater than 10% of the amount of suspended and deposited solid particles in the ocean, the sedimentation of solid particles in sewage on the seabed should be investigated and predicted. This investigation should be carried out in accordance with the relevant provisions of GB17378.5. 7 Drainage pipes and diffusers
7.1 General
Drainage pipes and diffusers are important components of sewage discharge pipelines. In addition to considering natural conditions, their design should also consider the current social and economic situation, development needs and their impact on the marine environment. Various factors affecting their safety and efficiency should also be fully and comprehensively considered.
7.2 Design requirements
7.2.1 The discharge of urban sewage should be designed in the short term and long term according to urban planning. The calculation period for the short-term sewage discharge fan is 10 years, and the calculation period for the long-term sewage discharge is at least 20 years. On the basis of the above planning, determine the scale of the sewage discharge project and the diameter of the sewage pipe. The construction of the project can be carried out in stages. The sewage discharge capacity of the sea discharge pipe should be designed according to the long-term sewage angle, and intermittent discharge should be adopted to achieve the self-purification flow rate.
7.2.2 A comparative analysis of the construction costs of sewage treatment plants and sewage sea discharge pipelines should be carried out to fully consider the economic bearing capacity and social and economic benefits of the construction of sewage discharge projects. 7.2.3 Establish a sewage and rainwater separation interception and treatment system to reduce the burden of the sea discharge pipeline and save money. 7.2.4 In the design of the pipeline system, the design internal pressure is used as the basis for calculating the maximum internal pressure. It should be able to withstand the maximum possible external pressure. The design temperature range of the pipeline is -20℃～tu℃.
7.2.5 The normal use and installation design states should be considered separately, and the pipeline system should be designed for these two states according to the load conditions. The design should ensure the function of the pipeline system under the design conditions and prevent possible structural failure or damage. 7.2.6 The structural analysis model of the pipeline system should be able to accurately simulate the main features of the real structural system, including loads, support conditions and structural characteristics. The mechanical calculation of the pipeline system should be carried out according to the requirements of statics, dynamics, material strength theory, fracture mechanics and damage mechanics. 7.2.7 The strength, stability and fatigue safety indicators of all pipeline accessories under working loads and environmental loads should not be lower than those required by the pipeline.
7.2.8 The material for manufacturing sewage pipes should be selected based on sewage characteristics, service life, water temperature, freezing conditions, pipe diameter, pressure inside and outside the pipe, soil quality, hydrodynamic conditions, erosion, and engineering costs. 7.2.9 If the sewage discharge needs to turn, its angle should be greater than 120°. 7.2.10 The buried depth of the sewage discharge pipeline to the sea should be calculated according to the number and tonnage of ships passing through the buried area, the size and weight of the pipe, the outer diameter and wall thickness of the pipe, and the scouring effect of the tide and current on the seabed. 7.2.11 According to the pipeline laying form, that is, surface laying or seabed burial, an appropriate diffuser should be used. 7.2.12 When calculating the length of the discharge pipe, the discharge pipe should be perpendicular to the flow direction of the sea current, and the water depth at the end of the discharge arm should be greater than 10°. It should be ensured that the edge of the plume generated when the sewage discharged from the first hole of the diffuser reaches the water surface does not touch the coast. 7.2.13 The length and orifice design of the diffuser should meet the specified initial dilution multiple requirements (about 100 times), and the characteristic parameter of the diffuser dilution function should not be less than 150 times.
7.2.14 The length of the diffuser is closely related to the dilution effect. The length of the diffuser is expressed by the following formula: Lb = 4.27Q5h -2/g172
Wherein:
la——diffuser length, in meters (m); Q--sewage discharge, in cubic meters per second (t/s); π--the maximum buoyancy height of sewage, in meters (m); &--reduced gravity acceleration, in meters per square second (m/s); S. initial dilution.
-+( b )
7.2.15 The flow velocity in the diffuser should reach the self-purification flow velocity, that is, not less than 0.6 m/s, and generally can be taken as about 0.8 m/s~1.0 m/s. The diffuser laid on the seabed layer should be equipped with a flap gate at the end, which is closed at ordinary times and opened when flushing. 7.2.16 The diffuser should be composed of several pipes with decreasing diameters to maintain the self-cleaning flow rate of the diffuser. 7.2.17 The spacing between the diffuser nozzles is approximately equal to 1/3 of the depth from the nozzle to the water surface. The nozzle spacing should be less than the diffuser length to meet the requirement that the sewage discharged from each nozzle does not overlap each other during the initial dilution and diffusion process. The calculation formula for the number of nozzles is as follows: 31-u
Wu Zhong:
Lp--diffuser effective length, in meters (m);-…sewage discharge depth, in meters (m). +-+-*++--(?)
7.2.18 The determination of the nozzle aperture should meet the requirements of sewage dilution and diffusion to ensure that large-sized suspended matter in the sewage can pass smoothly. In areas where sediment accumulates rapidly, there should be a sprinkler to prevent sediment from blocking the diffuser mouth. The outflow rate of the nozzle should be large enough. When designing, the Fr should be greater than 1.0, and the nozzle aperture should be 5cm to 23cm. The aperture of the nozzle on the i-th diffuser is calculated as follows: cf
rCpV2gE
The outflow velocity of sewage at the nozzle on the first diffuser: Ua = Cp V2gE:
—Flow rate of the i-th hole H:
Cp——Outflow coefficient of the nozzle on the first pipe; g Gravitational acceleration, in meters per square second (m/): F, the eddy diffusion coefficient at the discharge port (X-i). (8)5 Normal use and installation design conditions should be considered separately, and the pipeline system should be designed for these two conditions according to the load conditions. The design should ensure the function of the pipeline system under the design conditions and prevent possible structural failure or damage. 7.2.6 The structural analysis model of the pipeline system should be able to accurately simulate the main characteristics of the real structural system, including load, support conditions and structural characteristics. The mechanical calculation of the pipeline system should be carried out according to the requirements of statics, dynamics, material strength theory, fracture mechanics and damage mechanics. 7.2.7 The strength, stability and fatigue safety indicators of all pipeline accessories under working loads and environmental loads should not be lower than the indicators required by the pipeline.
7.2.8 The material for manufacturing sewage pipes should be selected according to factors such as sewage characteristics, service life, water temperature, freezing conditions, pipe diameter, pressure inside and outside the pipe, soil quality, hydrodynamic conditions, erosion, and engineering costs. 7.2.9 If the sewage discharge needs to turn, its angle should be greater than 120°. 7.2.10 The buried depth of the sewage discharge pipeline to the sea should be calculated according to the number and tonnage of ships passing through the buried area, the size and weight of the pipe, the outer diameter and wall thickness of the pipe, and the scouring effect of the tide and current on the seabed. 7.2.11 According to the pipeline laying form, that is, surface laying or seabed burial, an appropriate diffuser should be used. 7.2.12 When calculating the length of the discharge pipe, the discharge pipe should be perpendicular to the flow direction of the sea current, and the water depth at the end of the discharge arm should be greater than 10°. It should be ensured that the edge of the plume generated when the sewage discharged from the first hole of the diffuser reaches the water surface does not touch the coast. 7.2.13 The length and orifice design of the diffuser should meet the specified initial dilution multiple requirements (about 100 times), and the characteristic parameter of the diffuser dilution function should not be less than 150 times.
7.2.14 The length of the diffuser is closely related to the dilution effect. The length of the diffuser is expressed by the following formula: Lb = 4.27Q5h -2/g172
Wherein:
la——diffuser length, in meters (m); Q--sewage discharge, in cubic meters per second (t/s); π--the maximum buoyancy height of sewage, in meters (m); &--reduced gravity acceleration, in meters per square second (m/s); S. initial dilution.
-+( b )
7.2.15 The flow velocity in the diffuser should reach the self-purification flow velocity, that is, not less than 0.6 m/s, and generally can be taken as about 0.8 m/s~1.0 m/s. The diffuser laid on the seabed layer should be equipped with a flap gate at the end, which is closed at ordinary times and opened when flushing. 7.2.16 The diffuser should be composed of several pipes with decreasing diameters to maintain the self-cleaning flow rate of the diffuser. 7.2.17 The spacing between the diffuser nozzles is approximately equal to 1/3 of the depth from the nozzle to the water surface. The nozzle spacing should be less than the diffuser length to meet the requirement that the sewage discharged from each nozzle does not overlap each other during the initial dilution and diffusion process. The calculation formula for the number of nozzles is as follows: 31-u
Wu Zhong:
Lp--diffuser effective length, in meters (m);-…sewage discharge depth, in meters (m). +-+-*++--(?)
7.2.18 The determination of the nozzle aperture should meet the requirements of sewage dilution and diffusion to ensure that large-sized suspended matter in the sewage can pass smoothly. In areas where sediment accumulates rapidly, there should be a sprinkler to prevent sediment from blocking the diffuser mouth. The outflow rate of the nozzle should be large enough. When designing, the Fr should be greater than 1.0, and the nozzle aperture should be 5cm to 23cm. The aperture of the nozzle on the i-th diffuser is calculated as follows: cf
rCpV2gE
The outflow velocity of sewage at the nozzle on the first diffuser: Ua = Cp V2gE:
—Flow rate of the i-th hole H:
Cp——Outflow coefficient of the nozzle on the first pipe; g Gravitational acceleration, in meters per square second (m/): F, the eddy diffusion coefficient at the discharge port (X-i). (8)5 Normal use and installation design conditions should be considered separately, and the pipeline system should be designed for these two conditions according to the load conditions. The design should ensure the function of the pipeline system under the design conditions and prevent possible structural failure or damage. 7.2.6 The structural analysis model of the pipeline system should be able to accurately simulate the main characteristics of the real structural system, including load, support conditions and structural characteristics. The mechanical calculation of the pipeline system should be carried out according to the requirements of statics, dynamics, material strength theory, fracture mechanics and damage mechanics. 7.2.7 The strength, stability and fatigue safety indicators of all pipeline accessories under working loads and environmental loads should not be lower than the indicators required by the pipeline.
7.2.8 The material for manufacturing sewage pipes should be selected according to factors such as sewage characteristics, service life, water temperature, freezing conditions, pipe diameter, pressure inside and outside the pipe, soil quality, hydrodynamic conditions, erosion, and engineering costs. 7.2.9 If the sewage discharge needs to turn, its angle should be greater than 120°. 7.2.10 The buried depth of the sewage discharge pipeline to the sea should be calculated according to the number and tonnage of ships passing through the buried area, the size and weight of the pipe, the outer diameter and wall thickness of the pipe, and the scouring effect of the tide and current on the seabed. 7.2.11 According to the pipeline laying form, that is, surface laying or seabed burial, an appropriate diffuser should be used. 7.2.12 When calculating the length of the discharge pipe, the discharge pipe should be perpendicular to the flow direction of the sea current, and the water depth at the end of the discharge arm should be greater than 10°. It should be ensured that the edge of the plume generated when the sewage discharged from the first hole of the diffuser reaches the water surface does not touch the coast. 7.2.13 The length and orifice design of the diffuser should meet the specified initial dilution multiple requirements (about 100 times), and the characteristic parameter of the diffuser dilution function should not be less than 150 times.
7.2.14 The length of the diffuser is closely related to the dilution effect. The length of the diffuser is expressed by the following formula: Lb = 4.27Q5h -2/g172
Wherein:
la——diffuser length, in meters (m); Q--sewage discharge, in cubic meters per second (t/s); π--the maximum buoyancy height of sewage, in meters (m); &--reduced gravity acceleration, in meters per square second (m/s); S. initial dilution.
-+( b )
7.2.15 The flow velocity in the diffuser should reach the self-purification flow velocity, that is, not less than 0.6 m/s, and generally can be taken as about 0.8 m/s~1.0 m/s. The diffuser laid on the seabed layer should be equipped with a flap gate at the end, which is closed at ordinary times and opened when flushing. 7.2.16 The diffuser should be composed of several pipes with decreasing diameters to maintain the self-cleaning flow rate of the diffuser. 7.2.17 The spacing between the diffuser nozzles is approximately equal to 1/3 of the depth from the nozzle to the water surface. The nozzle spacing should be less than the diffuser length to meet the requirement that the sewage discharged from each nozzle does not overlap each other during the initial dilution and diffusion process. The calculation formula for the number of nozzles is as follows: 31-u
Wu Zhong:
Lp--diffuser effective length, in meters (m);-…sewage discharge depth, in meters (m). +-+-*++--(?)
7.2.18 The determination of the nozzle aperture should meet the requirements of sewage dilution and diffusion to ensure that large-sized suspended matter in the sewage can
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