CEEB313 – WATER & WASTE WATER
ENGINEERING
DESIGN OF A WATER RETICULATION FOR
SECONDARY DISTRIBUTION SYSTEM
TABLE CONTENT
BIL
TITLE
PAGE
1
INTRODUCTION
2
2
IMPACT OF THE SECONDARY
DISTRIBUTION SYSTEM
8
3
DESIGN AND CALCULATION
13
4
CONCLUSION
26
1.0: INTRODUCTION
The secondary water distribution system is used as a link between the main distribution pipe and the house connection including the fire hydrants.The design must achieve the sufficient preassure and quantity of water in the most cost effective manner. The transmission of water from the source or water treatment plant to the various consumers is usually done in two stages, distribution and reticulation.
The former term is generally used to describe the system of bigger (or trunk) mains, reservoirs and, in some situations, pumping systems. In bigger systems such as in cities, the distribution function is well-defined and often operated separately. In large systems or where water is delivered to separate water suppliers, the initial delivery can be through bulk or trunk mains. The term reticulation is normally used to describe the street mains and connections to properties. However, use of these terms does tend to be interchangeable.
The distribution system is designed to:
reliably distribute bulk water supplies to the suburbs, or supply points provide water at the correct elevation and/or pressure
buffer the diurnal peaks in demand from the consumers
maintain the water quality.
To achieve these objectives, particular combinations of reservoir storage, ring mains and pumping arrangements are used, depending upon the system topography and size.
A distribution system may also be made up of distribution zones. A distribution zone is a part of the distribution system in which all consumers receive drinking-water of identical quality, from the same or similar sources, with the same treatment and usually at the same pressure and is usually clearly separated from other parts of the network, generally by location, but in some cases by the layout or composition of the pipe network. In these Guidelines the term distribution system is used to include specific zones.
Developing a system to distribute water to customers is a big investment for a community. Because a water distribution system is intended to serve a community for more than
50 years and it is buried and difficult to access, careful planning and consideration is needed. Water distribution systems have three major components: pipes, valves, and flush hydrants. Each part plays a role in ensuring adequate water service and in maintaining quality water.
Because the pipes and valves are buried, a detailed map is needed to gain quick access to the system for maintenance and repairs. A map is also an important planning tool for upgrades and expansions. It is common for an experienced operator or town employee to have detailed knowledge of the location of all distribution system components. Relying solely on memory, however, can put the distribution system at risk if problems occur when the responsible person is unavailable. A detailed map ensures that the investment in the community infrastructure is documented, and can be studied and shared with interested parties.
Water pipes should be laid out in loops to avoid dead-ends that create stagnant water. Water pipes must be buried at least 48 inches below the ground surface in Ohio to protect them from freezing.
Two types of water pipes are needed in a water system—transmission lines and distribution lines. Transmission lines are the pipes that carry the water from the source to the storage system. Transmission lines are the largest, thickest pipes in the system making them the most expensive. When planning a water system, try to keep the treatment and storage tanks close to the water source to reduce the cost of transmission lines.
Distribution pipes carry water out to the users. To protect water quality, water pipes must be at least 10 feet from sewer pipes and laid in separate trenches. The absolute minimum diameter for a distribution pipe is two inches. A six-inch diameter pipe is the minimum needed for fire flows and for serving fire hydrants.
Since water pipes will be used for at least 50 years, most communities look ahead to expanded service and often use bigger pipe than the minimum. Too large a pipe, however, can lead to water quality problems. If water stands too long in large pipes, the chlorine residual diminishes, metals can dissolve in the water, and biological films can grow.
Values are a critical part of a water system and are often an afterthought. Valves isolate portions of the water system for servicing. By carefully considering the placement of valves, water system repairs and maintenance can be conducted with minimal loss of service.
Valves that are not used for years may not function when the need arises. Valves can stick and even break if neglected. A valve exercise program is a necessary part of water distribution system maintenance.
c) Flush Hydrants
Flush hydrants are the most visible part of the water distribution system. They must be at the end of all lines to remove accumulated corrosion products from dead-ends. Flush hydrants should also be installed throughout the system to provide for periodic flushing to maintain high water quality. Sometimes people mistake flush hydrants for fire hydrants. Fire hydrants are larger and are often connected to larger pipes.
d) Critical points in a distribution system
Critical points are those points where procedures for equipment failure would lead to a public health hazard. Specific critical points are discussed in this chapter to highlight and differentiate the types of risk that are present in a distribution system. There are two types of critical points in the distribution system, those critical to continuity of supply and those critical to water contamination.
Water contamination is an obvious and direct risk to public health. It can occur directly by intrusion of contaminants into the system or by chemical reactions within the system (such as chemical reactions with the pipe structure). The contamination of water within the distribution system is discussed in detail in this chapter
Supply loss is also a critical point for public health, but is not the subject of these Guidelines. For the initial time (say several hours), the risks to the community are not those of thirst, they are those of fire fighting, minimal interruptions to industry, inadequacy of water for flushing away sewage, and for personal hygiene. The factors that could lead to supply loss include:
loss of source water supply
treatment failure
water main failure
service reservoir valve operation: inlet fails to open, drain fails to close
water contamination, meaning supply must be stopped.
Emergency storage is required in order to continue supply when the inlet main is broken, during upstream system maintenance, or during some other loss of supply situation.
In practice, most supply losses involve a dual failure: a mechanical/electrical defect or human error that occurs and an alarm system that fails to provide warning in time to take corrective action. Therefore the alarm system needs regular testing and valves need regular working and testing, and staff needs regular training. Situations that can lead to loss of supply should be addressed in the water safety plan or other appropriate manual.
2.0 : IMPACT OF THE SECONDARY DISTRIBUTION SYSTEM
The drinking water industry is striving to implement new regulations for secondary disinfection to prevent unwanted microbial contamination in the distribution system while minimizing the formation of disinfectant by-products (DBPs). From a public health perspective the need to increase disinfectant residual concentrations and/or switch disinfectants will be a critical factor indeveloping these regulations. However, these decisions can potentially lead to significant degradation of both water quality and distribution system materials via corrosion.
Aesthetic Effects
Odor and Taste are useful indicators of water quality even though odor-free water is not necessarily safe to drink. Odor is also an indicator of the effectiveness of different kinds of treatment. However, present methods of measuring taste and odor are still fairly subjective and the task of identifying an unacceptable level for each chemical in different waters requires more study. Also, some contaminant odors are noticeable even when present in extremely small amounts. It is usually very expensive and often impossible to identify, much less remove, the odor-producing substance.
Standards related to odor and taste: Chloride, Copper, Foaming Agents, Iron, Manganese pH, Sulfate, Threshold Odor Number (TON), Total Dissolved Solids, Zinc.
Color may be indicative of dissolved organic material, inadequate treatment, high disinfectant demand and the potential for the production of excess amounts of disinfectant by-products. Inorganic contaminants such as metals are also common causes of color. In general, the point of consumer complaint is variable over a range from 5 to 30 color units, though most people find color objectionable over 15 color units. Rapid changes in color levels may provoke more citizen complaints than a relatively high, constant color level.
Standards related to color: Aluminum, Color, Copper, Foaming Agents, Iron, Manganese, Total Dissolved Solids.
Foaming is usually caused by detergents and similar substances when water has been agitated or aerated as in many faucets. An off-taste described as oily, fishy, or perfume-like is commonly associated with foaming. However, these tastes and odors may be due to the breakdown of waste products rather than the detergents themselves.
Standards related to foaming: Foaming Agents. Cosmetic Effects
Skin discoloration is a cosmetic effect related to silver ingestion. This effect, called argyria, does not impair body function, and has never been found to be caused by drinking water in the United States. A standard has been set, however, because silver is used as an antibacterial agent in many home water treatment devices, and so presents a potential problem which deserves attention.
Standard related to this effect: Silver.
Tooth discoloration and/or pitting is caused by excess fluoride exposures during the formative period prior to eruption of the teeth in children. The secondary standard of 2.0 MG/L is intended as a guideline for an upper boundary level in areas which have high
levels of naturally occurring fluoride. The level of the SMCL was set based upon a balancing of the beneficial effects of protection from tooth decay and the undesirable effects of excessive exposures leading to discoloration. Information about the Centers for Disease Control's (CDC) recommendations regarding optimal fluoridation levels and the beneficial effects for protection from tooth decay can be found on its Community Water Fluoridation page.
Standard related to this effect: Fluoride. Technical Effects
Corrosivity, and staining related to corrosion, not only affect the aesthetic quality of water, but may also have significant economic implications. Other effects of corrosive water, such as the corrosion of iron and copper, may stain household fixtures, and impart objectionable metallic taste and red or blue-green color to the water supply as well. Corrosion of distribution system pipes can reduce water flow.
Standards related to corrosion and staining: Chloride, Copper, Corrosivity, Iron, Manganese, pH, Total Dissolved Solids, Zinc.
Scaling and sedimentation are other processes which have economic impacts. Scale is a mineral deposit which builds up on the insides of hot water pipes, boilers, and heat exchangers, restricting or even blocking water flow. Sediments are loose deposits in the distribution system or home plumbing.
Standards related to scale and sediments: Iron, pH, Total Dissolved Solids, Aluminum.
Although state health agencies and public water systems often decide to monitor and treat their supplies for secondary contaminants, federal regulations do not require them to do this. Where secondary contaminants are a problem, the types of removal technologies discussed below are corrective actions which the water supplier can take. They are usually effective depending upon the overall nature of the water supply.
Corrosion control is perhaps the single most cost-effective method a system can use to treat for iron, copper and zinc due to the significant benefits in
1. reduction of contaminants at the consumer's tap,
2. cost savings due to extending the useful life of water mains and service lines,
3. energy savings from transporting water more easily through smoother, uncorroded pipes, and
4. reduced water losses through leaking or broken mains or other plumbing.
This treatment is used to control the acidity, alkalinity or other water qualities which affect pipes and equipment used to transport water. By controlling these factors, the public water system can reduce the leaching of metals such as copper, iron, and zinc from pipes or fixtures, as well as the color and taste associated with these contaminants. It should be noted that corrosion control is not used to remove metals from contaminated source waters.
Conventional treatments will remove a variety of secondary contaminants. Coagulation (or flocculation) and filtration removes metals like iron, manganese and zinc. Aeration removes odors, iron and manganese. Granular activated carbon will remove most of the contaminants which cause odors, color, and foaming.
Non-conventional treatments like distillation, reverse osmosis and electrodialysis are effective for removal of chloride, nitrates, total dissolved solids and other inorganic substances. However, these are fairly expensive technologies and may be impractical for smaller
systems.Non-treatment options include blending water from the principal source with uncontaminated water from an alternative source.
Contaminant SecondaryMC L
Noticeable Effects above the Secondary MCL
Aluminum 0.05 to
0.2mg/L*
colored water
Chloride 250 mg/L salty taste
Color 15 color units visible tint
Copper 1.0 mg/L metallic taste; blue-green staining
Corrosivity Non-corrosive metallic taste; corroded pipes/ fixtures staining
Fluoride 2.0 mg/L tooth discoloration
Foaming agents 0.5 mg/L frothy, cloudy; bitter taste; odor
Iron 0.3 mg/L rusty color; sediment; metallic taste; reddish or orange staining
Manganese 0.05 mg/L black to brown color; black staining; bitter metallic taste
Odor 3 TON
(threshold odor number)
"rotten-egg", musty or chemical smell
pH 6.5 - 8.5 low pH: bitter metallic taste; corrosion high pH: slippery feel; soda taste; deposits
Silver 0.1 mg/L skin discoloration; graying of the white part of the eye
Sulfate 250 mg/L salty taste
Total Dissolved Solids (TDS)
500 mg/L hardness; deposits; colored water; staining; salty taste
Zinc 5 mg/L metallic taste
A new township development developed by PKNS located in Daerah Hulu Selangor, Selangor Darul Ehsan. There comprises of256 unit of single storey terrace house, day school for 700 students, surau for 300 person and wet market of 22 stall.By reffer the table 6.3, water consumption can be calculated as follow.The calculation which done for and :
Type of Development Water
Consumption Rate
No. of Units Total Water Consumption (L/d)
Single Storey Terrace Houses 1300 256 332,800 Surau 50 300 15,000 Day School 50 700 35,000 Wet Market 1500 22 33,000 TOTAL 415,800
So for convert Water Demand Total Water Demand, Q =
FOR calculating : Peaking factor = 2.5
12.03 L/s
AVERAGE FLOW AND FIRE FLOW (CASE 2) :
Fire Flow: 1140 L/s (19 L/s)(UTG) Q = 4.813 L/s + 19.0 L/s = 23.81 L/s
Designing of the nodes the loops design base on two cases which are the peak flow case and average flow + fire flow. The needed fire flow is the rate of water flow required for firefighting to confine a major fire to the buildings within a block or other group complex with minimal loss. From the guidelines for developers, we get that it is equal to 1140 L/d in which we convert it to L/s and get a value of 19L/s. The head pressure loss is 100.84 according to the plan layout. However, on the other side we have to get the flow at each node after we get the actual pressure head loss. Therefore, we need to design the nodes and draw the pipes to construct through software called EPANET.
4.0 : CONCLUSION
Finally, by using the software called EPANET, we have finished the design of a water reticulation for secondary distribution system. The system was designed based on average flow case and peak flow case. The values for the average flow case and peak flow case were 23.81 L/s and 12.03 L/s respectively. In both cases, the designs were designed with the same length of pipes and diameters. The only difference made was the base demand at each nodes. For both design there are a total number of junction and pipes are 39 and 48 respectively.
5.0 REFERENCES http://water.epa.gov/drink/contaminants/secondarystandards.cfm http://books.google.com.my/books? id=NeTmfhOfdAwC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=one page&q&f=false https://www.linkedin.com/groups/hi-how-fix-negative-pressure-3780529.S.111621301 EPANET MANUAL EPANET 2.0 https://www.youtube.com/watch? v=RyxOjo7siNg&index=8&list=PLB2780D59FE4D2065
