DRINKING WATER DISTRIBUTION SYSTEM

Class Lecture Package -2

WATER DISTRIBUTION SYSTEM

Drinking water distribution system is a combination of components used to supply safe water to individual households

It collects treated water from treatment plant Household plumbing systems are also part of

distribution system

WATER DISTRIBUTION SYSTEM

WTPTransmission

Distribution network

Elevated storage tank

COMPONENTS OF DS

Pumping station Structural Electrical Pumping Piping

Distribution storage Tanks Pipe Valve

Distribution piping Pipes Valves

HYDRAULICS, PRESSURIZED FLOW

It is the flow (full) that is passed through the pipes

It needs the concepts of fluid mechanics and hydraulics to analyze the flow

Full flow

Partial flow

DESIGN OF PIPELINES

The construction of pipes involve large costs Needs modeling/predicting the behaviour

Experimental systems (model prototype) Numerical models

Cost Time Safety Ease of modification Aid to communication

TYPICAL HEADLOSS DIAGRAM

H

EGL

HYDRAULICS,PUMP

Pumps are integral components of a distribution system

It supplies the energy needed

Conditions and performance assessment is critical

Pump system carve is typically used for design

DischargeH

e

a

d

HYDRAULICS, DS

It uses the concept of pressurized flow Air bubbles can arise in the water Pipe breaks, leaks can cause variations in the

hydraulic calculations It considers steady state flows Hardy cross method is typically used hydraulic

analysis of pipe network

PIPELINE FRICTION EQUATION

Hazen-William equation

US unit

SI unit

V = velocity

C = roughness coefficient

R = hydraulic radius

S = friction headloss

TYPICAL VALUES OF CPipe material Value of CPVC 135-150Steel (mortar lining) 120-145Steel (unlined) 110-130Ductile iron (mortar lining) 100-140Ductile iron (unlined) 80-120Asbestos cement 120-130Concrete 130-140

TYPICAL DISTRIBUTION NETWORK

1

2 4

53

HARDY CROSS METHOD

It is a widely used method to calculate hydraulic behavior of a pipe network Head loss can also be computed

It is a trial and error procedure Very useful for large scale computation in computer

APPLICATION OF MODELS

Model selection Network representation Calibration Verification Problem definition Model application Display/analysis

HYDRAULICS, STORAGE

Storage is provided to ensure Reliability of supply Maintain pressure Improve operational flexibility and efficiency

Floating vs pumped storage Location of storage is important for efficient

use/supply of water

HYDRAULICS, STORAGE

Tank levels Settling overflow level Identifying service area Identifying pressure zone

Tank volume Fire and emergency storage demand

CORROSION

Corrosion is a big concern for water distribution systems

Typical three types of corrosion observed in distribution system Internal corrosion Microbial influenced corrosion Leaching

TYPICAL CORROSION IN DS

Metallic MIC Leaching

Metal Major Unknown Minor

Polymeric none Unknown Major

Cement based

major Unknown Major

METALLIC CORROSION

Both Internal and external corrosion are very common in metallic pipes

Three conditions required Metallic surface An oxidant Medium to transport the oxidant to the metal

MIC

It is caused by microbiological activity Some researchers feel biofilms protect metallic surface

from natural corrosion Presence and structure of biofilms

Hydraulic condition Nutrient availability Residual disinfectant Roughness of pipe

LEACHING

Leaching is typically defined as the release of material to water without involving conventional corrosion processes

Typical examples are metal bearing corrosion scales, monomers or calcium from cement matrix

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FACTORS AFFECTING CORROSION

Flow velocity Temperature pH Alkalinity Dissolved oxygen Total dissolved solids Hardness Bacteria

INDICATORS OF CORROSION

pH, alkalinity and calcium concentration indicate the potential of corrosion

Pipe inspection, analysis of pipe scales help to understand the potential for corrosion

Many indexes used Langelier Saturation Index Aggressive Index Ryznar Index Driving force index

CORROSION CONTROL

Controlling corrosion is a big challenge in water distribution

The presence of different material in the same DS can bring additional issues to reduce the corrosion Corrosion control mechanisms can cause harm to

some materials

CORROSION CONTROL

Typical corrosion control techniques Corrosion inhibitors

Orthophosphate Changes in water quality to reduce Lining on pipe surface/change pipe material

The chemicals used during water treatment process can affect the effectiveness

CONTROLLING MIC

Controlling MIC is basically controlling the formation of biofilms

Changes in water quality helps in controlling microbial growth in biofilm

Chlorine is not effective in destruction of biofilms Shock chlorination work at some materials

PIPE MATERIALS

Pipe materials can play an important part in the quality and quantity of water in DS

Pipes provides External and internal integrity of DS Interact with water quality

There are many different types of materials used in distribution system

CAST IRON

Historically, it is the most widely used material Lined unlined

The use of cast iron pipes for new construction is virtually non existent Pipe break problems Water quality problems

GRAY CAST IRON

It is an iron alloy centrifugally cast in sand or metal molds Large amount of carbon present Low melting point

Installation of these pipes have stopped in early 1970s

It has flat flakes

GRAY CAST IRON

The flakes reduces its strength Brittle in nature, not elastic

It is very weak in tension Two ways manufactured

Spun cast pipes Pit cast pipes

TYPES OF FAILURE IN GRAY CI PIPES

Wedge Splitting Spiral Cracking Corrosion Pitting Longitudinal Cracking Circumferential Breaks Bell SplitsVisit http://irc.nrc-cnrc.gc.ca/ui/bu/grayfailuretype_e.htmlTo see the details

DUCTILE IRON

Due to various limitations and problems associated with gray cast iron, ductile irons are being used since 1960s

Ductile iron is more elastic than cast irons It is made by adding small amount of magnesium and

controlling the manufacturing condition It is also very common as a material for distribution

system

STEEL

Steel pipes are typically used for large diameter pipes Transmission pipes

High strength, elastic and shock resistant It is relatively expensive It is more corrosion resistant than other iron

based pipes

CONCRETE

Concrete is inert, safe, long-lived and dependable

Different types of pipes used Steel cylinder Prestressed Noncylinder Pretensioned

ASBESTOS CEMENT CONCRETE

Source of durable and inexpensive piping Maintenance requirement is relatively high Many municipalities are looking for ways reduce

the maintenance costs Replacement of failed pipes

Due to environmental concerns, no new construction of AC pipes

PVC

Polyvinyl chloride is the most commonly used material for construction of new distribution systems

It is resistant to corrosion High strength to weight ratio Low historical information regarding its service

LINING

Lining is very important to reduce the pipe water interaction in various distribution systems

Low cost Long life Sustained smoothness Cement mortar lining common for iron pipes

LINING

Lining thickness plays an important role in determining effectiveness

It can be slowly attacked at soft water Coatings provides resistant to corrosion Leaching of cement mortar can be a concern in

some places

HW-2 Review an article by groups

Article review guideline is posted on ilearn The guideline is quite comprehensive. All the items may

not be applicable for your particular review. Do what applies to you

Everyone needs to review the articles themselves. The writing portion can only be shared by group members

Conduct the review within 2 pages Due: will be discussed in the class

Articles for Review Chlorine dioxide disinfection technology to avoid bromate

formation in desalinated seawater in potable waterworksBelluati, M.; Danesi, E.; Petrucci, G.; Rosellini, M. Source:Desalination, v 203, n 1-3, p 312-318, Febrary 5, 2007

Copper pipe failure by microbiologically influenced corrosionCantor, Abigail F. ; Bushman, James B.; Glodoski, Martin S.; Kiefer, Eric; Bersch, Randy; Wallenkamp, Hank Source: Materials Performance, v 45, n 6, p 38-41, June 2006

Effect of pipe corrosion scales on chlorine dioxide consumption in drinking water distribution systemsZhang, Zhe; Stout, Janet E.; Yu, Victor L.; Vidic, RadisavSource: Water Research, v 42, n 1-2, p 129-136, January 2008

Articles for Review Effect of chlorine on corrosion in drinking water systems

Cantor, Abigail F.; Park, Jae K.; Vaiyavatjamai, Prasit Source: Journal / American Water Works Association, v 95, n 5, p 112-122, May 2003

Options for recarbonation, remineralisation and disinfection for desalination plantsWithers, Anthony Source: Desalination, v 179, n 1-3 SPEC. ISS., p 11-24, July 10, 2005

Disinfecting the Coquitlam water supply: Ozone and UV disinfectionLandis, Heather; Neemann, Jeff; Hulsey, Bob; Fiorante, Reno; Neden, Doug; Singh, Inder Source: Ozone: Science and Engineering, v 29, n 4, p 287-290, July 2007

SELECTION OF PIPE MATERIAL

Service conditions Pressure Soil loads Corrosion potential of

soil Corrosive nature of

water

Availability Local availability Experienced

installation Sizes and thickness Compatibility with

available fittings

SELECTION

Properties of pipe Strength Ductility Corrosion resistance Fluid friction

resistance

Economics Cost Required life Cost of maintenance

and repairs

PERCENTAGE OF PIPE MATERIAL USED

Country CI DI AC Steel Plastic/PVC

Concrete Others

Canada 42 12 24 4 15 4 2US 46 11 20 1 14 2 3UK 81 10 2 6 1Germany 55 9 5 30 1Spain 30 50 4 15 1Netherlands 16 40 3 40 1

PIPES IN REGINA DISTRIBUTION SYSTEM

The distribution system is composed of different types of materials

The dominant material is AC Other materials used are Cast iron, PVC and

Steel Most of the distribution system are constructed in

the last 30 years

LEAD

Lead as household plumbing 20% of all service connections in US have lead Lead as a plumbing material is also widely used in

Canada Due to health concerns, there are no new

plumbing done with lead

LEAD

Lead based alloys are also used in plumbing Most of the existing lead connections are old Leaching of lead is common from household plumbing Changes in water chemistry play an important role in

the leachability of lead pipes Corrosion inhibitors are used to reduce the leachability

of lead

COPPER

Copper is also very common as household plumbing Since 1963, 5.3 million miles of copper tubing

installed in US households Also common in Canada

Copper based alloys are also used in joints and plumbing systems

COPPER

Copper also has leachability issues in water The leached copper can often goes through

typical wastewater treatment processes End up in wastewater sludge Concern for disposal of sludge

Flushing is often required in the morning before drinking water

PVC

PVC is very popular as household plumbing material for new construction

It has less corrosion problem than other conventional plumbing material

PVC is considered to be inert with the changes in water quality

WATER QUALITY ASPECTS

Water travels hours, or even days from the time it leaves the treatment to reach individual household Uncertainty of maintaining similar water quality in the

distribution system There are different types of reactions occurred

inside this large reactors

WQ ASPECTS

Pipe material can interact with the water to change the quality Iron oxidation/reduction encourage the presence of

iron and sulphate reducing bacteria (MIC) Cross connections can challenge the quality of

water in the distribution system

WQ ASPECTS

Water Distribution Systems Handbook

WATER TREATMENT CHEMICALS

Four major sources of chemicals in water treatment Coagulants Disinfectants Corrosion inhibitors Oxidants for chemical oxidation

WATER TREATMENT AND DS

The effect of coagulant types on the distribution system integrity has been explored limitedly

The effect of disinfectants on the distribution system has been investigated in detail Chlorine is more corrosive on the distribution system

than other disinfectants

WATER TREATMENT AND DS

Corrosion inhibitors are typically effective on specific materials It may deteriorate other types of materials in the distribution

system Zinc orthophosphate also increases zinc concentrations in

water The effects of other chemicals on the quality of water

are not explored in detail

WQ CHALLENGE IN DIFFERENT MATERIALS

Water Distribution Systems Handbook

DISINFECTION

Disinfectants serve two purposes Restrict microbial regrowth Protect from microbial intrusion from cross connection

Disinfectant concentration decreases over time due to protection from microbes Microbes however grows in biofilms Reaction with organic

DISINFECTION AND DBP

Disinfectants react with organic matter to form byproducts DBPs formed during water treatment process remain

in water (depending upon DBP formation kinetics) The reaction to form DBP continues in the

distribution systems

CHALLENGING INTERACTIONS

Corrosion control, microbial inactivation and DBPs all interact with each other

Optimization needed to manage these challenges

Corrosion Control

Microbial Inactivation

DBPs

WATER QUALITY MONITORING

Mechanism for identifying variations in water quality over time and space

The resulting database can also be used to model the distribution system behavior

Specialized monitoring can also support specific research objectives

WQ MONITORING

Monitoring can be conducted in three different ways Laboratory based Real time monitoring Online monitoring

Online monitoring is gaining popularity due to ease of operation

WQ MONITORING

Routing monitoring Regulatory requirements Sampling methods Sampling parameters

Synoptic monitoring Specific requirements

US REGULATORY LIMITS FOR WQ

Water Distribution Systems Handbook

WQ, STORAGE

Water quality can be affected in the storage Three different types of problems typically

observed Chemical Microbiological Physical

CHEMICAL PROBLEMS IN STORAGE

Loss of disinfectant residual Formation of DBPs Development of taste and odor Increase in pH Corrosion Buildup of iron and manganese Occurrence of hydrogen sulfide Leachate from internal coatings

OTHER PROBLEMS

Microbiological Bacterial regrowth Nitrification Worms and insects

Physical Sediment buildup Entry of contaminants temperature

MONITORING WQ IN STORAGE

Routine monitoring Typical parameters Nitrification Sediment Biofilm

Specialized monitoring can also be done based on the specific requirements

WQ, CONSTRUCTION & OPERATION

Numerous factors can have an impact on water quality in distribution system

Appropriate construction and operation practices can reduce the chances of WQ failures

Most standard operating procedures take care of these aspects

DISINFECTION OF NEW PIPES

Water mains are expected to be sterile in the construction site

Disinfection chemicals Liquid chlorine Sodium hypochlorite Calcium hypochlorite

Appropriate disinfection procedure need to be adopted Among other considerations are testing new mains,

repairs and disposal of highly chlorinated water

DISINFECTION OF STORAGE TANKS

Three different disinfection methods are used for filling tanks Water disinfected Tank disinfected Mixed

Underwater inspection is used for controlling the quality

CROSS CONNECTION CONTROL

It is any connection between a potable water systems and source of contamination

Backflow prevention techniques are used to control cross-connection

Typical backflow prevention Air gap Reduced pressure Atmospheric and pressure vacuum breakers

FLUSHING DS

Flushing is done using a hydrant or blowoffs to improve water quality Removes sediment, eliminate low chlorine, solve taste, odour

and turbidity problems Flushing can be enhanced by closing valves to

maximize velocity in pipes Switching disinfectants can improve the effectiveness of

DS cleaning

MODELING WATER QUALITY

Water quality modeling complements monitoring programs Monitoring programs are limited in distribution

system Thousands of miles of distribution systems Widespread monitoring programs are expensive and at

many case not feasible It can also be useful for prediction of water quality

WATER QUALITY MODELING

The presence of storage tanks bring lot of variability in hydraulic and water quality behaviour of the system Depending upon the water level in the storage tanks,

the quality of water may be affected Water quality modeling may not be as precise as

results from monitoring programs

EFFECTIVENESS OF WQ MODELS

Fraction of water originating from a particular source

Age of water in the system Concentration of nonreactive tracer compound

either added or removed from the system Concentration and loss rate of secondary

disinfectant

EFFECTIVENESS OF WQ MODELS

The concentration and growth rate of DBPs Number and mass of attached and free flowing

bacteria Indirect benefits

Complementing hydraulic models Help design of tanks and pipes Minimize risk associated with DBPs

WQ MODELS

Typical water quality models are steady state in nature Useful for contaminant movement at constant condition

WQ models are coupled with hydraulic models Common models

EPANET CYBERNET H2ONET Stoner synerGEE

GOVERNING EQUATIONS

The actual physical system is modeled as a network of links connected at nodes

Links are pipes, pumps or valves

Nodes are junction, source, consumption and storage points

ADVECTIVE TRANSPORT IN PIPES

Ci = concentration in pipe I as a function of distance x and time t

ui = flow velocity in pipe Ir(Ci) = rate of reaction as a function of

concentration

MIXING IN PIPE JUNCTIONS

i = link with flow leaving node k,Ik = set of links with flow into k,Lj = length of link j,Qj = flow in link jQk,ext = external source flow entering the network at node kCk, ext =concentration of the external flow entering at node

k

TYPES OF MODELS

Steady state models Assumes that hydraulic conditions do not change Storage does not affect water quality Simple to setup and solve

Dynamic models Takes account of hydraulic changes More accurate than steady state models

CASE STUDY

System modeling Design of the field study Results of the field study Verification study Presampling procedure Analysis of results Modeling of chlorine residual

MAPS OF CHESHIRE SERVICE AREA

Water Distribution Systems Handbook

ACTUAL VS PREDICTED FLURIDE CONCENTRATION

Water Distribution Systems Handbook

QUESTIONS ??