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Student Publications
Author: Senthil Seliyan Elango
Title:
Urban Water Management (Final Thesis)
Area:
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Acknowledgements
I would like to thank AIU academic staff for invaluable support and
advice, offered
throughout this study. Special thanks also go to Mr. Gilroy Newball
for his interest in
and review of my assignments.
Mr. Kimberly Roff is thanked for her determination in reviewing each
of my program
evaluations, and for offering helpful commentary along the way.
I use this opportunity to thank the members of staff of The Atlantic
International
University for the opportunity to design and implement an
educational path for myself
that suits my intellectual and professional goals and is mutually
exclusive to the
pursuits of others.
I want to express a special thanks to Dr. Franklin Valcin for his
professional guidance
through the phases of this process and to acknowledge him has one of
the true
pioneers of Distance Learning globally.
I am indeed grateful to the other administrative staffs of the
Atlantic International
University who have facilitated me with financing my education.
Special thanks also go to my family and friends for their unending
support and good
cheer.
3
ABSTRACT
Thesis Goals and Specific Objectives
The goal of urban water management thesis to investigate components
of urban water
system and careful, economic use handling of the water in urban. The
first goal of this
thesis is to evaluate the waste and storm water management in urban.
The second goal
of the thesis is to recommend storm water management strategies for
urban residential
areas.
The sub-objectives that lead to the achievement of these goals are:
To explore various components of urban water supply system.
To explore number of
concepts about waste management which vary in their
usage between countries or regions.
To explore the need for storm water management and/or water
conservation
practices in urban residential areas.
To explore how storm water initiatives in the urbans.
To develop an evaluative framework based on the principles of
summative/formative program evaluation, policy instrument
evaluation, and
community-based social marketing;
To develop performance measures and interview questions based on the
criteria identified in the evaluative framework;
To obtain interview responses from homeowners/program participants
regarding their experience with a storm water or water conservation
program;
4
INTRODUCTION
Urban water infrastructure typically includes water collection and
storage facilities at
source sites, water transport via aqueducts (canals, tunnels and/or
pipelines) from
source sites to water treatment facilities; water treatment, storage
and distribution
systems; wastewater collection (sewage) systems and treatment; and
urban drainage
works. This is illustrated as a simple schematic in Figure. Generic
simulation models
of components of urban water systems have been developed and are
commonly
applied to study specific component design and operation issues.
Increasingly,
optimization models are being used to estimate cost-effective
designs and operating
policies. Cost savings can be substantial, especially when applied
to large complex
urban systems (Dandy and Engelhardt, 2001; Savic and Walters, 1997).
Figure. Schematic showing urban surface water source, water
treatment prior to urban
use, and some sources of nonpoint urban drainage and runoff and its
impacts.
Most urban water users require high-quality water, and natural
surface and/or
groundwater supplies, called raw water, often cannot meet the
quality requirements of
domestic and industrial users. In such situations, water treatment
is required prior to
its use. Once it is treated, urban water can then be stored and
distributed within the
urban area, usually through a network of storage tanks and pipes.
5
Pipe flows in urban distribution systems should
be under pressure to prevent
contamination from groundwater's and to meet various user and fire
protection
requirements. After use, the `wastewater' is collected in a network
of sewers, or in
some cases ditches, leading to a wastewater treatment plant or
discharge site. In many
urban areas the sewage system has a dual function. The sewers
collect both
wastewater from households and the runoff from streets and roofs
during storm
events. However, the transport capacity of the sewer network and the
treatment
facilities are limited. During intense rainfall, overflows from the
sewage system
discharge a mixture of surface runoff and wastewater to the surface
waters. This has a
negative impact on the water quality of urban surface waters.
Wastewater treatment plants remove some of the impurities in the
wastewater before
it is discharged into receiving water bodies or on land surfaces.
Water bodies
receiving effluents from point sources such as wastewater treatment
plants may also
receive runoff from the surrounding watershed area during storm
events. The
pollutants in both point and non-point discharges will affect the
quality of the water in
those receiving water bodies.
This thesis briefly describes these urban water system components
and reviews some
of the general assumptions incorporated into optimization and
simulation models used
to plan urban water systems. The focus of urban water systems
modeling is mainly on
the prediction and management of quantity and quality of flows and
pressure heads in
water distribution networks, wastewater flows in gravity sewer
networks, and on the
design efficiencies of water and wastewater treatment plants. Other
models can be
used for the real-time operation of various components of urban
systems.
DESCRIPTION
Main Components of an urban water system
Collecting water
The entire area from which a stream or river receives its water is
called a catchment.
A catchment is a natural drainage area, bounded by sloping ground,
hills or
mountains, from which water flows to a low point.
Virtually everybody lives in a catchment, which may include hundreds
of sub-
catchments. What happens in each of the smaller catchments will
affect the main
catchment.
The water that comes out of a tap once flowed across a catchment �
and that is why
catchments are a crucial part of urban water systems.
The quality of the catchment determines the quality of the water
harvested from it.
Few communities have pristine water sources and the quality of water
from most
sources is at risk from activities occurring in the catchment.
6
Storing water
In some urban water systems, the water supply is obtained directly
from a river or
another body of freshwater. In others, rivers are dammed and the
water supply is
distributed from artificial storages, such as reservoirs.
Dams are built across rivers and streams to create reservoirs to
collect water from
catchments to ensure sufficient supply will be available when
needed. Dams also have
been built for a range of purposes besides water supply, such as
agriculture and
hydro-electricity generation.
Water may also be released from a reservoir as an "environmental
flow" to maintain
the health of the ecosystem downstream of the reservoir. It is
estimated that the
significant reservoirs built around the world store five billion
megalitres of water.
Transporting water
Water is transported from catchments to communities by a variety of
means including
pipelines, aqueducts, and open channels or via natural waterways.
Treating water
Before water is used for human consumption, its harmful impurities
need to be
removed. Communities that do not have adequate water treatment
facilities, a
common problem in developing regions, often have high incidences of
disease and
mortality due to drinking contaminated water. A range of syndromes,
including acute
dehydrating diarrhoea (cholera), prolonged febrile illness with
abdominal symptoms
(typhoid fever), acute bloody diarrhoea (dysentery) and chronic
diarrhoea (Brainerd
7
diarrhoea). Numerous health organizations point
to the fact that contaminated water
leads to over 3 billion episodes of diarrhoea and an estimated 2
million deaths, mostly
among children, each year.
Contaminants in natural water supplies can also include
microorganisms such as
Cryptosporidium and Giardia lamblia as well as inorganic and organic
cancer-causing
chemicals (such as compounds containing arsenic, chromium, copper,
lead and
mercury) and radioactive material (such as radium and uranium).
Herbicides and
pesticides reduce the suitability of river water as a source of
drinking water. Recently,
traces of hormonal substances and medicines detected in river water
are generating
more and more concern.
To remove impurities and pathogens, a typical municipal water
purification system
involves a sequence of processes, from physical removal of
impurities to chemical
treatment. Physical and chemical removal processes include initial
and final filtering,
coagulation, flocculation, sedimentation and disinfection, as
illustrated in the
schematic of Figure.
As shown in Figure, one of the first steps in most water treatment
plants involves
passing raw water through coarse filters to remove sticks, leaves
and other large solid
objects.
Sand and grit settle out of the water during this stage. Next a
chemical such as alum is
added to the raw water to facilitate coagulation. As the water is
stirred, the alum
causes the formation of sticky globs of small particles made up of
bacteria, silt and
other impurities. Once these globs of matter are formed, the water
is routed to a series
of settling tanks where the globs, or floc, sink to the bottom. This
settling process is
called flocculation.
After flocculation, the water is pumped slowly across another large
settling basin. In
this sedimentation or clarification process, much of the remaining
floc and solid
material accumulates at the bottom of the basin. The clarified water
is then passed
through layers of sand, coal and other granular material to remove
microorganisms �
including viruses, bacteria and protozoa such as Cryptosporidium �
and any
remaining floc and silt. This stage of purification mimics the
natural filtration of water
as it moves through the ground.
8
Fig. Typical processes in water treatment plants.
The filtered water is then treated with chemical disinfectants to
kill any organisms
that remain after the filtration process. An effective disinfectant
is chlorine, but its use
may cause potentially dangerous substances such as carcinogenic
trihalomethanes.
Alternatives to chlorine include ozone oxidation (Figure). Unlike
chlorine, ozone does
not stay in the water after it leaves the treatment plant, so it
offers no protection from
bacteria that might be in the storage tanks and water pipes of the
water distribution
system.
Water can also be treated with ultraviolet light to kill
microorganisms, but this has the
same limitation as oxidation: it is ineffective outside of the
treatment plant. Figure
13.3 is an aerial view of a water treatment plant serving a
population of about
50,000.Sometimes calcium carbonate is removed from drinking water in
order to
prevent it from accumulating in drinking water pipes and washing
machines. In arid
coastal areas desalinated brackish or saline water is an important
source of water for
high-value uses. The cost of desalination is still high, but
decreasing steadily. The two
most common methods of desalination are distillation and reverse
osmosis.
9
Distillation requires more energy, while
osmosis systems need frequent maintenance
of the membranes.
The distribution system
After water has been treated to protect public health, improve
aesthetics by removing
color and taste and odour as required, it is ready to be delivered
to consumers. The
system of mains and pipes used to deliver the water is known as the
distribution, or
reticulation, system.
Treated water may be held at a treatment plant or immediately
discharged into the
system of mains and pipes that will transport it to consumers' taps.
On the way it may
be held in short-term storages, usually known as service reservoirs,
which are located
as close as possible to where the water will be used.
Sufficient water is required in a local area to supply periods of
high demand, as on a
hot summer day. From a design perspective, the needs of fire
services usually
determine the capacity of the system.
An important characteristic of a drinking water distribution system
is that it is closed,
to prevent contamination by birds, animals or people. In contrast,
irrigation water is
usually delivered in open channels or aqueducts.
A significant part of the water supply system lies buried
underground. Out of the
public eye, such infrastructure can be overlooked. It is easy to
forget how valuable
and essential water distribution systems are to the community. In
terms of money
spent on supplying water in Australia, most of it has been invested
in the mains and
pipes buried under the streets of towns and suburbs across the
country.
Most distribution systems have developed and expanded as urban areas
have grown.
A map of a water distribution system would show a complex mixture of
tree-like and
looped pipe networks, together with valves and pumps.
Distribution systems require regular cleaning (flushing and
scouring), maintenance
and a program to replace pipes and other equipment as they near the
end of their
useful lives. Water mains can be expected to have a useful life of
40 to 100 years.
Many of the pipes under the older parts of our cities may be towards
the upper end of
this range.
Challenges in Urban Water Management
The challenges in urban water management are ample. In the
developing world there
is still a significant fraction of the population that has no access
to proper water
supply and sanitation. At the same time population growth,
urbanization and
industrialization continue to cause pollution and depletion of water
sources. In the
developed world pollution of water sources is threatening the
sustainability of the
10
urban water systems. Climate change is likely
to affect all urban centers, either with
increasingly heavy storms or with prolonged droughts, or both. To
address the
gigantic challenges it is crucial to develop good approaches, so
that policy
development and planning are directed towards addressing these
global change
pressures, and to achieving truly sustainable urban water systems.
Current approach as described in international policy documents
The `Dublin Statement' (International Conference on Water and the
Environment,
1992) and the `Agenda 21' (UN Department for Sustainable
Development, 1992)
unfold a vision about how water resources are best managed, to serve
the people,
without damaging the environment. The `Dublin Statement' formulated
a number of
principles that since have formed the basis for Integrated Water
Resources
Management (IWRM). IWRM addresses the issue of water management from
a river
basin perspective, since this is the scale that includes (all)
relevant cause-effect
relations and stakeholder interests. The principles of the `Dublin
Statement' are:
Fresh water is a finite and vulnerable resource, essential to
sustain life,
development and the environment. Management of water resources
requires linking social and economic development with environmental
protection, within the river basin or catchment area.
Water development and management should be based on a participatory
approach, involving users, planners and policy-makers at all levels.
Decisions are taken at the lowest appropriate level, with full
public
consultation and involvement of users in planning and
implementation.
Women play a central part in the provision, management and
safeguarding
of water. Institutional arrangements should reflect the role of
women in
water provision and protection. Empowerment of women to participate
in
decision-making and implementation, as defined by them, needs to be
addressed.
Water has an economic value in all its competing uses and should be
recognized as an economic good. Access to clean water and sanitation
at
an affordable price is a basic right of all human beings. Failure to
recognize the economic value of water in the past has led to
wasteful use
and environmental damage.
These principles were applied to the urban environment as well and a
future city was
envisaged where appropriate water charges are in place, which will
help reduce water
scarcity and will reduce the need for developing ever more distant
(and costly)
sources. Waste discharge controls must be enforced and cannot be
seen as reasonable
trade-offs for prosperity brought by industrial growth
(International Conference on
Water and the Environment, 1992).
Innovative approaches in urban water management
The Bellagio Statement
Several projects, programmes and approaches go a step further than
the WFD. One of
these is the `Bellagio Statement', formulated by the Environmental
Sanitation
Working Group of the WSSCC in 2000. Its principles are believed to
be essential for
11
achieving the objective of worldwide access to
safe environmental sanitation and a
healthy urban water system (reference):
1. Human dignity, quality of life and environmental security should
be at the centre of
the new approach, which should be responsive and accountable to
needs and demands
in the local setting.
� Solutions should be tailored to the full spectrum of social,
economic, health and
environmental concerns � the household and community environment
should be
protected � the economic opportunities of waste recovery and use
should be harnessed
2. In line with good governance principles, decision-making should
involve
participation of all stakeholders, especially the consumers and
providers of services.
Decision-making at all levels should be based on informed choices �
incentives for
provision and consumption of services and facilities should be
consistent with the
overall goal and objective � rights of consumers and providers
should be balanced by
responsibilities to the wider human community and environment
3. Waste should be considered a resource, and its management should
be holistic and
form part of integrated water resources, nutrient flows and waste
management
processes.
� Inputs should be reduced so as to promote efficiency and water and
environmental
security � exports of waste should be minimized to promote
efficiency and reduce the
spread of pollution � wastewater should be recycled and added to the
water budget
4. The domain in which environmental sanitation problems are
resolved should be
kept to the minimum practicable size (household, community, town,
district,
catchment, city) and wastes diluted as little as possible.
� Waste should be managed as close as possible to its source � water
should be
minimally used to transport waste � additional technologies for
waste sanitization and
reuse should be developed
GENERAL ANALYSIS
Waste water
Waste management is
the collection, transport,
processing,
recycling or
disposal of
waste materials. The term usually relates to materials produced by
human activity,
and is generally undertaken
to reduce their effect
on health,
aesthetics or
amenity.
Waste management is also carried out to reduce the materials' effect
on the
environment and to recover
resources
from them. Waste management can involve
solid,
liquid or gaseous
substances, with different methods and fields of expertise for
each.
Waste management
practices differ for developed
and developing nations, for
urban
and rural areas,
and for residential and
industrial,
producers. Management for non-
hazardous
residential and institutional waste in metropolitan areas is
usually the
responsibility of
local
government authorities, while management for non-hazardous
commercial and industrial waste is usually the responsibility of the
generator.
Waste management methods vary widely between areas for many reasons,
including
type of waste material, nearby land uses, and the area available.
12
Disposal
Landfill
Disposing of waste in a landfill involves burying waste to dispose
of it, and this
remains a common practice in most countries. Historically, landfills
were often
established in disused
quarries, mining
voids or borrow pits. A properly-designed and
well-managed landfill can be a hygienic and relatively inexpensive
method of
disposing of waste materials. Older, poorly-designed or
poorly-managed landfills can
create a number of adverse environmental
impacts such as wind-blown litter,
attraction of vermin,
and generation of liquid
leachate. Another
common byproduct of
landfills is gas (mostly composed of
methane and
carbon dioxide),
which is produced
as organic waste breaks down anaerobically. This gas can create odor
problems, kill
surface vegetation, and is a greenhouse gas.
Design characteristics of a modern landfill include methods to
contain leachate such
as clay or plastic lining material. Deposited waste is normally
compacted to increase
its density and stability, and covered to prevent attracting
vermin (such as
mice or
rats). Many
landfills also have landfill gas extraction systems installed to
extract the
landfill gas.
Gas is pumped out of the landfill using perforated pipes and flared
off or
burnt in a gas
engine to generate
electricity.
Many local authorities, especially in rural areas, have found it
difficult to establish
new landfills due to opposition from owners of adjacent land. As a
result, solid waste
disposal in these areas must be transported further for disposal or
managed by other
methods. This fact, as well as growing concern about the
environmental impacts of
excessive materials consumption, has given rise to efforts to
minimize the amount of
waste sent to landfill in many areas. These efforts include taxing
or levying waste sent
to landfill, recycling waste products, converting waste to energy,
and designing
products that use less material.
Incineration
Incineration is a disposal method
that involves combustion of waste material.
Incineration and other high temperature waste treatment systems are
sometimes
described
as "thermal treatment". Incinerators convert waste materials
into heat, gas,
steam, and
ash.
Incineration is carried out both on a small scale by individuals and
on a large scale by
industry. It is used to dispose of solid, liquid and gaseous waste.
It is recognized as a
practical method of disposing of certain
hazardous
waste materials (such as biological
medical waste).
Incineration is a controversial method of waste disposal due to
issues
such as emission of gaseous
pollutants.
Incineration is common in countries such as
Japan where land is more
scarce, as these facilities generally do not require as much
area as landfills.
Waste-to-energy (WtE) or energy-from-waste (EfW) are broad terms for
facilities that
burn waste in a furnace or boiler to generate heat, steam and/or
electricity. Modern
combustion technologies maintain the advantages of incineration
without its
numerous disadvantages, while providing a clean energy source.
Installation of a
"boiler" such as the
RCBC
(rotary cascading bed combustor) allows the consumption
of problem waste as fuels for the generation of
electricity.
Municipal solid waste,
sewage,
sludge,
"dirty coals", and coal
byproducts, are
cleanly and efficiently
13
consumed for
energy
production with
emissions well within strict regulatory
standards. The fly
ash byproduct is inert, and can be mixed
with compost.
Tridel SA, a public corporation, is a modern waste-to-energy plant
in Lausanne,
Switzerland. It
provides both electrical and thermal energy, totaling about 60
MW. It
uses an oscillating firebed. The emitted gases are treated to reach
as low as about 10%
of the permitted values of pollutants as regulated by the severe
Swiss legislation,
except for NOx, which is held at 50%. The water used is collected
mostly from roofs
and paved areas and all waste water conforms to strict standards.
Solid waste is
mostly treated clinker plus washed fly ash and is almost inert,
occupying about 10%
of the volume of the original compacted
municipal waste
and other sources. Heavy
metals,
including mercury,
are extracted and sent by rail for recycling. A unique
feature is that much of the waste arrives by rail, through a
purpose-built 4 km tunnel;
as the plant is built about 250 m higher than the lake, this avoids
the pollution from
numerous trucks per day climbing the steep hill. Environmentally,
Tridel SA supplies
almost 10% of the electricity consumed in its catchment area at full
output, from a
renewable fuel. Economically, it is viable.
Waste management concepts
There are a number
of concepts about waste management which vary in their usage
between countries or regions. This section presents some of the most
general, widely-
used concepts.
Waste hierarchy
The waste hierarchy refers to the "3 Rs"
reduce,
reuse and
recycle, which
classify
waste management strategies according to their desirability in terms
of waste
minimization. The waste hierarchy remains the cornerstone of
most waste
minimization strategies. The aim of the waste hierarchy is to
extract the maximum
practical benefits from products and to generate the minimum amount
of waste.
Extended producer responsibility
Extended Producer Responsibility (EPR) is a strategy designed to
promote the
integration of all costs associated with products throughout their
life cycle (including
end-of-life disposal costs) into the market price of the product.
Extended producer
responsibility is meant to impose accountability over the entire
lifecycle of products
and packaging introduced to the market. This means that firms which
manufacture,
import and/or sell products are required to be responsible for the
products after their
useful life as well as during manufacture.
Polluter pays principle
The Polluter Pays Principle is a principle where the polluting party
pays for the
impact caused to the natural environment. With respect to waste
management, this
generally refers to the requirement for a waste generator to pay for
appropriate
disposal of the waste.
14
Urban Wastewater Management: The Outlook for
the Future
Urban wastewater management is at a critical juncture in the United
States and
elsewhere. Methods must again change in response to urban
development, population
growth, and diminishing natural resources. Based on information in
recent literature,
current research focuses, and trends in the engineering and
regulatory community,
three aspects of wastewater management are becoming increasingly
important now
and will continue to be important in the foreseeable future
development of wastewater
management. The three aspects are decentralized wastewater
management (DWM),
wastewater reclamation and reuse, and heightened attention to
wet-weather flow
(WWF) management. Currently, consideration of these three aspects in
wastewater
management planning is improving the functionality of wastewater
systems and
creating sustainable alternatives to the traditional centralized
SSSs.
The reduction in recent years of federal grant money for the
construction of
wastewater collection and treatment systems required municipalities
to search for
cost-effective wastewater management alternatives. In addition,
federal legislation
(e.g., the 1977 amendments to the Clean Water Act) required
communities to consider
alternatives to the conventional centralized sewer system, and
financial assistance was
made available. The requirement that municipal and industrial
discharges identify
cost-effective wastewater management solutions has curtailed the
sometimes blind
selection of centralized SSSs for newly urbanizing areas. And as
stated earlier, since
World War II newly urbanizing areas have been constructed with lower
density than
the historical urban areas for which centralized sewer systems were
originally
designed. The applicability of centralized management concepts in
these less-densely
populated urbanizing areas is questionable. The factors of
cost-effectiveness and
appropriateness have contributed to the development of alternative
wastewater
management methods including DWM technologies. Decentralized
wastewater
management (DWM) is defined as the collection, treatment, and reuse
of wastewater
at or near its source of generation. A significant improvement in
the newer
decentralized technologies compared to the decentralized privy
vault-cesspool system
of the nineteenth century is the ability to integrate seamlessly and
effectively with
water-carriage waste removal. From the public's perspective, the
primary deterrent to
implementation of alternative wastewater management technologies has
been the fear
of a life-style change. Most individuals desire wastewater
management to be
unobtrusive, convenient, and not to require significant maintenance
efforts on their
part. The newer decentralized technologies have been developed to
integrate easily
with traditional plumbing fixtures and do not require a significant
life-style
adjustment. Essentially, the core components of DWM are the same as
centralized
collection and treatment systems, but the applied technologies are
different. Water
carriage is still prevalent, but the wastewater is treated on site
or near the site and not
transported to a central treatment facility. Decentralized systems
currently serve
approximately 25 percent of the U.S. population, and approximately
37 percent of
new development. DWM systems have been shown to save money, to
promote better
watershed management, and to be suitable for a variety of site
conditions. Research
has improved the operation and management of septic tanks and
developed innovative
and improved on-site treatment technologies, e.g., intermittent and
recirculating
packed-bed filtration. The result has been the increased
implementation of DWM in
developing urban fringe areas, the same areas where centralized SSSs
would likely
15
have been implemented two decades earlier if
federal funding could have been easily
secured. From the policy making and regulatory perspective, the most
prominent
concern about DWM is the lack of a body of authority with the
appropriate powers to
operate, manage, and regulate the system in the same manner as a
centralized system.
Creating such a managing body would require changing the status quo
that has existed
for many years, something many think is not possible. The primary
difficulty in the
near future for DWM is anticipated to be overcoming the years of
institutional inertia
built up in favor of centralized SSSs. One additional issue
hindering the
implementation of DWM technologies is the limited basic design
requirements
available. Because of the newness of the current decentralized
technologies,
engineering textbooks and manuals do not yet have adequate coverage
of the
concepts. A period of several years is needed until the necessary
information is widely
available and the ideas become incorporated into standard
engineering practice.
The second wastewater management concept that will be important in
the future is
wastewater reuse. Wastewater reuse generally occurs on site or at
the end of a
centralized collection and treatment operation. The development of
local and on-site
wastewater reuse technologies will further encourage the use of DWM
technologies.
DWM, coupled with wastewater reuse, has the potential to be a highly
cost-effective
wastewater management method in less densely populated urbanizing
areas. Increased
reuse of wastewater at the end of a centralized collection and
treatment operation will
reduce the demand for water resources, but will not, in general,
promote the use of
alternative wastewater management options. Difficulties with
wastewater reuse
include public perception of selected uses for the reclaimed
wastewater and the need
to find economic uses of reclaimed wastewater and waste products.
Currently, reuse is
more attractive economically in the industrial setting than in the
residential setting.
But with growing populations and the future demands on potable water
in residential
areas, wastewater reuse will likely become more economical in
residential areas.
Managing the quantity and quality of wet-weather flow (WWF) is the
final issue
expected to significantly influence the development of wastewater
management in the
future. In the nineteenth and early twentieth centuries, WWF was
viewed as a
mechanism to cleanse the urban area of built-up filth on roadways
and in the sewers.
WWF gradually became viewed as wastewater when centralized SSSs
developed into
the wastewater management technology of choice in the early
twentieth century.
Separate storm-water discharges were observed to pollute waterways
and create
nuisance conditions. Even with some early recognition, it has taken
the better part of
the twentieth century for the importance of WWF in water quality
degradation to
become thoroughly documented. Currently, all wet weather induced
discharges (e.g.,
combined-sewer overflow (CSO), sanitary-sewer overflow (SSO), and
separate storm-
water discharges) are known to have detrimental effects on receiving
water. In the
late 1960s and throughout the 1970s, regulations were enacted in
response to the
documented effects of WWF on water quality degradation. The initial
step was the
1972 passage of the Federal Water Pollution Control Act Amendments,
which
established policies for controlling wastewater discharges in an
effort to protect water
quality and acknowledged storm water as significant. The extension
of the National
Pollution Discharge Elimination System (NPDES) to include municipal
separate
storm-water discharges in the 1990s is having a significant effect
on urban wastewater
management. The requirement of municipal and industrial storm-water
control and
the current direction of combined-sewer overflow (CSO) and
sanitary-sewer overflow
16
(SSO) policies suggest the need to reconsider
past wastewater management methods
and technologies that were developed before storm-water discharges,
CSO, and SSO
were water quality concerns.
Due to the widespread problems of CSO, there has been a massive
effort to control or
eliminate CSOs at the municipal, state, and federal level. The
improved understanding
of combined-sewer systems (CSS) has renewed the interest in the use
of centralized
CSSs in the United States and elsewhere under specific conditions.
Lessons learned
from past combined system problems have enlightened current
engineers and
improved the operation of existing systems. For example, CSSs can be
planned for
newly urbanizing areas of the appropriate density to take advantage
of new
construction to provide adequate inline and offline storage and
increased capacity at
the wastewater treatment facility. In addition, new construction of
wastewater
treatment facilities could be coordinated with the new CSSs to
accommodate the
increased sludge-handling capacity required. The improved storage
capacity coupled
with improved storm-water management would theoretically reduce CSO
frequency.
The SSO problem has also come under scrutiny over the past decade.
Most SSOs are
a result of excessive groundwater infiltration and storm-water
inflow (I/I) causing the
sewer system to be overwhelmed. Overflow structures provide the
necessary relief to
protect the integrity of the collection and treatment system, but
have an adverse effect
on the receiving water. During wet weather, a sanitary sewer conduit
taking on
excessive I/I essentially operates as a combined sewer. Millions of
dollars in fines
against a municipality can accumulate for SSO violations.
Investigations into the
causes of the SSO and the implementation of corrective actions could
also cost
millions of dollars. The level of funds required to address and
correct SSO problems
suggests the need to reduce wet-weather induced I/I in future
wastewater management
methods.
Studies in the past have compared the performance of centralized
combined- versus
separate-sewer systems. The results from the studies have shown
combined and
separate systems to discharge similar quantities of pollutants over
the long term,
suggesting that neither has environmental advantages. This is
similar to the
conclusions of Rudolph Hering's report to the National Board of
Health in 1880. The
need for a careful economic comparison between combined and separate
systems is
vital now that sanitary advantages are not as apparent. An unbiased
comparison of
combined and separate systems has renewed the interest in CSSs.
Heaney et al., for
example, reported that CSSs may discharge a smaller pollutant load
to the receiving
water than separate systems in cases where the storm water is
discharged untreated
and the sanitary wastewater is treated effectively. They presented
an example in
southern Germany where CSSs were being designed with extensive
infiltration
components to reduce the inflow of storm water to the drainage
systems, reducing the
frequency and magnitude of CSO events. CSSs are also used in
Switzerland and Japan
with similar results. In the United States, similar micro-management
techniques are
being used to improve the performance of CSSs. Proper planning of
micro-
management concepts, especially localized storm-water detention,
will improve the
performance of new CSSs, making them more attractive in the future.
17
Urban waste water disposal system management
Urban waste water disposal systems are very complex hydraulic
engineering systems
comprising a number of spatial elements with characteristic
parameters (natural part
of the basin, urbanized city space), hydrographic network with the
receptor, climatic
and hydrographic characteristics of the basin, sewage system and the
structures within
it, waste water treatment facilities, culturological and sociologic
properties of the
people living in the basin etc.Extremely complex and specific issues
of the urban
waste water disposal systems, due to their complexity, and
multidisciplinary
character, as well as due to a large number of influential
parameters, are nowadays,
successfully solved in the developed countries by the integral
management with the
application of the modern computer system and technologies. By the
integral solution
of the urban space problems, sewage system, waste water treatment
facilities
and the receptors (figure ), using the existing historical or
current data bases, modern
simulation and optimization models, careful planning and production
of appropriate
scenarios, nowadays the optimal high-efficiency strategies are
attained in the world,
their basic goal being the �hygienic� disposal of waste waters, that
is maximal
reduction of waste water outlets and of harmful effects on the
recipients and the
environment, with minimization of capital investments and
operational costs.
18
The basic characteristic of the modern solutions of the urban waste
water disposal
systems is a high level of influence of information and
communication technology in
the definition of the final solutions and in their application.
Nowadays, no one is able
to anticipate the speed and scope of the development of information
and
communication technologies with certainty, but their influence in
the future will
surely be very important.
The influence of the sewage system on the waste water treatment
facility, and on the
receptor due to the uncontrolled overflow of waste waters is very
significant. Because
of the high oscillations of hydraulic and biological load,
especially at unbalanced
sewage systems, particularly the efficiency of the biological part
of the waste water
facility is reduced and the large problems occur in its operation.
The experiences of
the developed countries demonstrate that there is no efficient
protection of the water
resources without efficient planning, dimensioning, organization,
management and
the work of the sewage system itself, and the modern solution of
urban waste waters
disposal systems and protection from pollution are based on this
fact.
Wastewater Treatment
The wastewater generated by residences, businesses and industries in
a community
consists largely of water. It often contains less than 10% dissolved
and suspended
solid material. Its cloudiness is caused by suspended particles
whose concentrations in
19
untreated sewage range from 100 to 350 mg/l.
One measure of the strength of the
wastewater is its biochemical oxygen demand, or BOD5. BOD5
is the amount of
dissolved oxygen aquatic microorganisms will require in five days as
they metabolize
the organic material in the wastewater. Untreated sewage typically
has a BOD5
concentration ranging from 100 mg/l to 300 mg/l. Pathogens or
disease-causing
organisms are also present in sewage. Coliform bacteria are used as
an indicator of
disease-causing organisms. Sewage also contains nutrients (such as
ammonia and
phosphorus), minerals and metals. Ammonia can range from 12 to 50
mg/l and
phosphorus can range from 6 to 20 mg/l in untreated sewage.
As illustrated in Figures 13.7 and 13.8, wastewater treatment is a
multi-stage process.
The goal is to reduce or remove organic matter, solids, nutrients,
disease-causing
organisms and other pollutants from wastewater before it is released
into a body of
water or on to the land, or is reused. The first stage of treatment
is called preliminary
treatment.
Preliminary treatment removes solid materials (sticks, rags, large
particles, sand,
gravel, toys, money, or anything people flush down toilets). Devices
such as bar
screens and grit chambers are used to filter the wastewater as it
enters a treatment
plant, and it then passes on to what is called primary treatment.
Clarifiers and septic tanks are generally used to provide primary
treatment, which
separates suspended solids and greases from wastewater. The
wastewater is held in a
tank for several hours, allowing the particles to settle to the
bottom and the greases to
float to the top. The solids that are drawn off the bottom and
skimmed off the top
receive further treatment as sludge. The clarified wastewater flows
on to the next,
secondary stage of wastewater treatment.
This secondary stage typically involves a biological treatment
process designed to
remove dissolved organic matter from wastewater. Sewage
microorganisms cultivated
and added to the wastewater absorb organic matter from sewage as
their food supply.
Three approaches are commonly used to accomplish secondary
treatment: fixed-film,
suspended-film and lagoon systems.
Fixed-film systems grow microorganisms on substrates such as rocks,
sand or plastic,
over which the wastewater is poured. As organic matter and nutrients
are absorbed
from the wastewater, the film of microorganisms grows and thickens.
Trickling filters,
rotating biological contactors and sand filters are examples of
fixed-film systems.
Suspended-film systems stir and suspend microorganisms in
wastewater. As the
microorganisms absorb organic matter and nutrients from the
wastewater, they grow
in size and number. After the microorganisms have been suspended in
the wastewater
for several hours, they are settled out as sludge. Some of the
sludge is pumped back
into the incoming wastewater to provide `seed' microorganisms. The
remainder is
sent on to a sludge treatment process. Activated sludge, extended
aeration, oxidation
ditch and sequential batch reactor systems are all examples of
suspended-film
systems. Lagoons, where used, are shallow basins that hold the
wastewater for
several months to allow for the natural degradation of sewage. These
systems take
advantage of natural aeration and microorganisms in the wastewater
to renovate
sewage.
Advanced treatment is necessary in some systems to remove nutrients
from
wastewater. Chemicals are sometimes added during the treatment
process to help
remove phosphorus or nitrogen. Some examples of nutrient removal
systems are
20
coagulant addition for phosphorus removal and
air stripping for ammonia removal.
Final treatment focuses on removal of disease-causing organisms from
wastewater.
Treated wastewater can be disinfected by adding chlorine or by
exposing it to
sufficient ultraviolet light. High levels of chlorine may be harmful
to aquatic life in
receiving streams, so treatment systems often add a
chlorine-neutralizing chemical to
the treated wastewater before stream discharge. Sludges are
generated throughout the
sewage treatment process. This sludge needs to be treated to reduce
odours, remove
some of the water and reduce volume, decompose some of the organic
matter and kill
disease-causing organisms. Following sludge treatment, liquid and
cake sludges free
of toxic compounds can be spread on fields, returning organic matter
and nutrients to
the soil.
Artificial wetlands and ponds are sometimes used for effluent
polishing. In the
wetlands the natural diurnal variation in the oxygen concentration
is restored.
Furthermore, artificial wetlands can reduce the nutrient content of
the effluent by the
uptake of nitrogen and phosphorus by algae or macrophytes. The
organic matter may
be harvested from the ponds and wetlands.
A typical model for the simulation of the treatment processes in
wastewater treatment
plants is the Activated Sludge Model (Gujer et al., 1999; Henze et
al., 1999;Hvitved-
Jacobsen et al., 1998). Activated sludge models predict the
production of bacterial
biomass and the subsequent conversion of organic matter and
nutrients into sludge,
CO2 and N2 gas.
Modern wastewater treatment
The basic principle treating the highly concentrated wastewater
occurring in small
volumes only is based on separating the domestic wastewater flow
applying modern,
low-energy membrane technology.
By advanced anaerobic technology (high-performance digestion) the
concentrate flow
is directly metabolized into biogas (methane, carbon dioxide) for
energy generation.
The filtrate flow, which is free of solids, is purified in modern
wastewater membrane
bioreactors. This anaerobic process step works with a high biomass
concentration
producing only little amounts of secondary sludge.
In the anaerobic high-performance digestion with integrated micro
filtration, the
organic mass is converted from highly-concentrated primary and
secondary sludge by
the microbial mineralization chain into CH4, CO2 and NH4. Due to the
high
concentration present, ammonia nitrogen can by economically recycled
from the
sludge fermentation procedure.
As already mentioned, the filtrate flow with the organic compounds
dissolved in it
undergoes anaerobic purification. This occurs in a high-performance
bioreactor with
biomass enrichment via membrane technology. The filtrate flow
generated is
hygienically harmless and reaches bathing water quality. It can be
directly infiltrated
into the ground or be used as process water.
After the second membrane separation stage, remaining nitrogen and
phosphorus
compounds are taken from the solids-free wastewater, whereby the
precipitation
product can also be recycled as a fertilizer.
21
Storm Water Management
In most urban areas, population is increasing rapidly and the issue
of supplying
adequate water to meet societal needs and to ensure equity in access
to water is one of
the most urgent and significant challenges faced by decision-makers.
With respect to
the physical alternatives to fulfill sustainable management of
freshwater, there are two
solutions: finding alternate or additional water resources using
conventional
centralized approaches; or better utilizing the limited amount of
water resources
available in a more efficient way. To date, much attention has been
given to the first
option and only limited attention has been given to optimizing water
management
systems.
Among the various alternative technologies to augment freshwater
resources,
rainwater harvesting and utilization is a decentralized,
environmentally sound
solution, which can avoid many environmental problems often caused
in conventional
large-scale projects using centralized approaches.
Rainwater harvesting, in its broadest sense, is a technology used
for collecting and
storing rainwater for human use from rooftops, land surfaces or rock
catchments using
simple techniques such as jars and pots as well as engineered
techniques. Rainwater
harvesting has been practiced for more than 4,000 years, owing to
the temporal and
spatial variability of rainfall. It is an important water source in
many areas with
significant rainfall but lacking any kind of conventional,
centralized supply system. It
22
is also a good option in areas where good
quality fresh surface water or groundwater
is lacking. The application of appropriate rainwater harvesting
technology is
important for the utilization of rainwater as a water resource.
Advantages of Rainwater Harvesting
Rainwater harvesting can coexist with and provide a good supplement
to
other water sources and utility systems, thus relieving pressure on
other water
sources.
Rainwater harvesting provides a water supply buffer for use in times
of
emergency or breakdown of the public water supply systems,
particularly
during natural disasters.
Rainwater harvesting can reduce storm drainage load and flooding in
city
streets.
Users of rainwater are usually the owners who operate and manage the
catchments system, hence, they are more likely to exercise water
conservation
because they know how much water is in storage and they will try to
prevent
the storage tank from drying up.
Rainwater harvesting technologies are flexible and can be built to
meet almost
any requirements. Construction, operation, and maintenance are not
labor
intensive.
Types of Rainwater Harvesting Systems
Typically, a rainwater harvesting system consists of three basic
elements: the
collection system, the conveyance system, and the storage system.
Collection systems
can vary from simple types within a household to bigger systems
where a large
catchments area contributes to an impounding reservoir from which
water is either
gravitated or pumped to water treatment plants. The categorization
of rainwater
harvesting systems depends on factors like the size and nature of
the catchment's areas
and whether the systems are in urban or rural settings. Some of the
systems are
described below
Catchment Areas
Rooftop catchments: In the most basic form of this technology,
rainwater is collected
in simple vessels at the edge of the roof. Variations on this basic
approach include
collection of rainwater in gutters which drain to the collection
vessel through down-
pipes constructed for this purpose, and/or the diversion of
rainwater from the gutters
to containers for settling particulates before being conveyed to the
storage container
for the domestic use. As the rooftop is the main catchment area, the
amount and
quality of rainwater collected depends on the area and type of
roofing material.
Reasonably pure rainwater can be collected from roofs constructed
with galvanized
corrugated iron, aluminium or asbestos cement sheets, tiles and
slates, although
23
thatched roofs tied with bamboo gutters and
laid in proper slopes can produce almost
the same amount of runoff less expensively (Gould, 1992). However,
the bamboo
roofs are least suitable because of possible health hazards.
Similarly, roofs with
metallic paint or other coatings are not recommended as they may
impart tastes or
color to the collected water. Roof catchments should also be cleaned
regularly to
remove dust, leaves and bird droppings so as to maintain the quality
of the product
water (see figure 1).
Land surface catchments: Rainwater harvesting using ground or land
surface
catchment areas is less complex way of collecting rainwater. It
involves improving
runoff capacity of the land surface through various techniques
including collection of
runoff with drain pipes and storage of collected water. Compared to
rooftop
catchment techniques, ground catchment techniques provide more
opportunity for
collecting water from a larger surface area. By retaining the flows
(including flood
flows) of small creeks and streams in small storage reservoirs (on
surface or
underground) created by low cost (e.g., earthen) dams, this
technology can meet water
demands during dry periods. There is a possibility of high
rates of water loss due to
infiltration into the ground, and, because of the often marginal
quality of the water
collected, this technique is mainly suitable for storing water for
agricultural purposes.
Various techniques available for increasing the runoff within ground
catchment areas
involve: i) clearing or altering vegetation cover, ii) increasing
the land slope with
artificial ground cover, and iii) reducing soil permeability by the
soil compaction and
application of chemicals (see figure 2).
24
Clearing or altering vegetation cover: Clearing vegetation from the
ground can
increase surface runoff but also can induce more soil erosion. Use
of dense vegetation
cover such as grass is usually suggested as it helps to both
maintain an high rate of
runoff and minimize soil erosion.
Increasing slope: Steeper slopes can allow rapid runoff of rainfall
to the
collector. However, the rate of runoff has to be controlled to
minimize soil erosion
from the catchment field. Use of plastic sheets, asphalt or tiles
along with slope can
further increase efficiency by reducing both evaporative losses and
soil erosion. The
use of flat sheets of galvanized iron with timber frames to prevent
corrosion was
recommended and constructed in the State of Victoria, Australia,
about 65 years ago
(Kenyon, 1929; cited in UNEP, 1982).
Soil compaction by physical means: This involves smoothing and
compacting
of soil surface using equipment such as graders and rollers. To
increase the surface
runoff and minimize soil erosion rates, conservation bench terraces
are constructed
along a slope perpendicular to runoff flow. The bench terraces are
separated by the
sloping collectors and provision is made for distributing the runoff
evenly across the
field strips as sheet flow. Excess flows are routed to a lower
collector and stored
(UNEP, 1982).
� Soil compaction by chemical treatments: In addition to clearing,
shaping and
compacting a catchment area, chemical applications with such soil
treatments as
sodium can significantly reduce the soil permeability. Use of
aqueous solutions of a
silicone-water repellent is another technique for enhancing soil
compaction
technologies. Though soil permeability can be reduced through
chemical treatments,
soil compaction can induce greater rates of soil erosion and may be
expensive. Use of
sodium-based chemicals may increase the salt content in the
collected water, which
may not be suitable both for drinking and irrigation
purposes.
Collection Devices
Storage tanks: Storage tanks for collecting rainwater harvested
using guttering may be
either above or below the ground. Precautions required in the use of
storage tanks
include provision of an adequate enclosure to minimize contamination
from human,
animal or other environmental contaminants, and a tight cover to
prevent algal growth
and the breeding of mosquitoes. Open containers are not recommended
for collecting
water for drinking purposes. Various types of rainwater storage
facilities can be found
in practice. Among them are cylindrical ferrocement tanks and mortar
jars. The
ferrocement tank consists of a lightly reinforced concrete base on
which is erected a
circular vertical cylinder with a 10 mm steel base. This cylinder is
further wrapped in
two layers of light wire mesh to form the frame of the tank. Mortar
jars are large jar
shaped vessels constructed from wire reinforced mortar. The storage
capacity needed
should be calculated to take into consideration the length of any
dry spells, the
amount of rainfall, and the per capita water consumption rate. In
most of the Asian
countries, the winter months are dry, sometimes for weeks on end,
and the annual
average rainfall can occur within just a few days. In such
circumstances, the storage
capacity should be large enough to cover the demands of two to three
weeks. For
example, a three person household should have a minimum capacity of
3 (Persons) x
90 (l) x 20 (days) = 5 400 l.
25
Rainfall water containers: As an alternative to
storage tanks, battery tanks (i.e.,
interconnected tanks) made of pottery, ferrocement, or polyethylene
may be suitable.
The polyethylene tanks are compact but have a large storage capacity
(ca. 1 000 to 2
000 l), are easy to clean and have many openings which can be fitted
with fittings for
connecting pipes. In Asia, jars made of earthen materials or
ferrocement tanks are
commonly used. During the 1980s, the use of rainwater catchment
technologies,
especially roof catchment systems, expanded rapidly in a number of
regions,
including Thailand where more than ten million 2 m3 ferrocement
rainwater jars were
built and many tens of thousands of larger ferrocement tanks were
constructed
between 1991 and 1993. Early problems with the jar design were
quickly addressed
by including a metal cover using readily available, standard brass
fixtures. The
immense success of the jar programme springs from the fact that the
technology met a
real need, was affordable, and invited community participation. The
programme also
captured the imagination and support of not only the citizens, but
also of government
at both local and national levels as well as community based
organizations, small-
scale enterprises and donor agencies. The introduction and rapid
promotion of
Bamboo reinforced tanks, however, was less successful because the
bamboo was
attacked by termites, bacteria and fungus. More than 50 000 tanks
were built between
1986 and 1993 (mainly in Thailand and Indonesia) before a number
started to fail,
and, by the late 1980s, the bamboo reinforced tank design, which had
promised to
provide an excellent low-cost alternative to ferrocement tanks, had
to be abandoned.
Conveyance Systems
Conveyance systems are required to transfer the rainwater collected
on the rooftops to
the storage tanks. This is usually accomplished by making
connections to one or more
down-pipes connected to the rooftop gutters. When selecting a
conveyance system,
consideration should be given to the fact that, when it first starts
to rain, dirt and
debris from the rooftop and gutters will be washed into the
down-pipe. Thus, the
relatively clean water will only be available some time later in the
storm. There are
several possible choices to selectively collect clean water for the
storage tanks. The
most common is the down-pipe flap. With this flap it is possible to
direct the first
flush of water flow through the down-pipe, while later rainfall is
diverted into a
storage tank. When it starts to rain, the flap is left in the closed
position, directing
water to the down-pipe, and, later, opened when relatively clean
water can be
collected. A great disadvantage of using this type of conveyance
control system is the
necessity to observe the runoff quality and manually operate the
flap. An alternative
approach would be to automate the opening of the flap as described
below.
A funnel-shaped insert is integrated into the down-pipe system.
Because the upper
edge of the funnel is not in direct contact with the sides of the
down-pipe, and a small
gap exists between the down-pipe walls and the funnel, water is free
to flow both
around the funnel and through the funnel. When it first starts to
rain, the volume of
water passing down the pipe is small, and the *dirty* water runs
down the walls of the
pipe, around the funnel and is discharged to the ground as is
normally the case with
rainwater guttering. However, as the rainfall continues, the volume
of water increases
and *clean* water fills the down-pipe. At this higher volume, the
funnel collects the
clean water and redirects it to a storage tank. The pipes used for
the collection of
rainwater, wherever possible, should be made of plastic, PVC or
other inert substance,
26
as the pH of rainwater can be low (acidic) and
could cause corrosion, and
mobilization of metals, in metal pipes.
In order to safely fill a rainwater storage tank, it is necessary to
make sure that excess
water can overflow, and that blockages in the pipes or dirt in the
water do not cause
damage or contamination of the water supply. The design of the
funnel system, with
the drain-pipe being larger than the rainwater tank feed-pipe, helps
to ensure that the
water supply is protected by allowing excess water to bypass the
storage tank. A
modification of this design is shown in Figure 5, which illustrates
a simple
overflow/bypass system. In this system, it also is possible to fill
the tank from a
municipal drinking water source, so that even during a prolonged
drought the tank can
be kept full. Care should be taken, however, to ensure that
rainwater does not enter
the drinking water distribution system.
GENERAL RECCOMMENDATION
Innovation Trends in Urban Water Supply and Sanitation.
Parallel with growing urban population drinking water demand
especially in mega
cities in the developing countries, is growing quickly and takes
increasing part of total
water resources of the world. In spite of the fact that urban
population uses only small
amount of available water for consumption, delivery of sufficient
water volumes
constitutes a difficult logistic and economical problem. In spite of
grate efforts during
several decades, still about 1.2 billion people in the developing
countries lack access
to safe drinking water supply. By the year 2050 an estimated 65% of
the world
population will live in areas of water shortage (Milburn, 1996).
Newer sources
(Knight, 1998) say that the pace of population growth is slowing
down and if this
trend will be continuing "only" 25 - 40 % of population will face
shortages of fresh
water.
There is a fundamental connection between present state in water
supply, sanitation,
organic waste management and agricultural development worldwide.
While
sustainable provision of water and sanitation for growing population
is in itself an
outstanding challenge, the new target is to develop technologies and
management
strategies that can make organic residuals from human settlements
useful in rural and
urban agriculture for production of food. Content of nutrients in
excreta of one person
is sufficient to produce grain with all nutrition necessary to
maintain life of just one
person.
Thus, theoretically, there is no reason for hunger for anybody.
Thus, it can be stated
that the need of increased agricultural production requires new
developments in
sanitation and solid waste handling technology to make recycling of
nutrients from
households to agriculture possible. Thus, methods of sanitation and
handling organic
solid wastes become a fundamental parts of water management
challenge representing
a crucial interface between type of sanitation, state of the
environment, health of
populations and food production.
Traditional methods used in water resources development and in
supply of sanitation
27
were and still are unable to satisfy fast
growing needs of developing countries. The
problem with supply of water and sanitation to growing urban
agglomerations has,
according International Water Resources Association already grown to
the scale of a
problem number one in the world (Milburn 1996). Solution of this
problem depends
on research and introduction of innovative technologies in water
sector and on long-
term national planning and development using technical, behavioral
and legislative
means. The new challenge is to adopt already emerging technical
solutions as well as
logistic and organizational methods and turn present problems to
opportunities. It is
clear that it may be possible to increase agricultural production
without increasing the
use of fossil fertilizers provided that sanitation technology could
be made capable of
recycling nutrients from households to agriculture. Water and
sanitation system
solutions known from developed countries are not only to expensive
in investments
and running costs to majority of developing countries but also does
not possess ability
to recycle
nutrients.
General outline of the complex solution and its necessary elements
have been already
defined and it is clear that such solutions will require rethinking
and innovation in
entire water and sanitation sector. It is also clear that the
majority of developing
countries will, even in spite of possible future economical
development, not copy
water and sanitation solutions known from developed world. At stake
is to much:
economical burden of such solutions versus possibility to increase
agricultural
production without use of fossil fertilizers and subsequent land
degradation. The
general goals of the future complex solution have been formulated
and several
elements is already under development. It is clear that in order to
alleviate problems
with water supply it is necessary to develop methods for multiple
and/or quality
dependent water use in households and introduce more efficient
economical
incentives to save water. It is also clear that some countries must
come back to ancient
habits to collect and use storm water for non-consumptive water
uses. For example
roof storm water may be used after separation of runoff from first
minutes if the
rainfall using simple mechanical devices.
Development of new technologies and innovative total water system
solutions for
urban areas is needed to satisfy present human needs with respect to
living standards
and the present environmental goals. These future system solutions
will encompass
water supply, quality-dependent water consumption, reuse of
rainwater, on-water-
borne sanitation and new methods of wastewater re-use in
agriculture. Decreasing
availability of clean water implies that water-borne sanitation is
not feasible solution
for any country not equipped with effective wastewater treatment,
and especially not
for countries in dry climate conditions. Two important tasks can be
listed in
connection to sanitation issue: first of all safe, cost-effective
and socially acceptable
water saving and safe sanitation alternatives or dry-sanitation
technologies should be
further developed and implemented, for the second it is necessary to
facilitate smooth,
long-term transition in which water-borne and dry sanitation
solutions exist parallel in
the same city. Since sanitation is mostly lacking not in central
parts of cities but in
suburban areas, introduction of dry sanitation may bring rapid and
low-cost
alternative to satisfy the needs of those less wealthy. Wider
introduction of dry
sanitation (including separation sanitation) solutions will require
increased research
28
efforts to adapt already developed solutions to
the varying local cultural and
economical conditions of developing countries. The challenge in this
context to create
socially and economically acceptable technologies of agricultural
uses of nutrients
present in human excreta.
Methods of safe and hygienic utilization wastewater from water-borne
sanitation
systems that are present in central parts of many large cities in
developing countries
have been discussed for a long time, but still there is no generally
accepted way for
utilization of wastewater in agriculture. The problem may be
technically addressed in
two ways: the first one is to introduce changes in water supply
systems e.g. for
example to introduce dual supply systems, one for less polluting
water uses and
second for heavily polluted uses such as sanitation where reused
water is used.
Effluents from less polluting uses could be directly used in
peri-urban agriculture
while wastewater from sanitation would be used only for irrigation
of non-
consumptive crops. Due to high costs of such solution, another
approach that is
discussed would manipulate on direct agricultural use of raw
wastewater. In
agricultural production of non-consumption crops wastewater could be
use without or
after primary treatment only, and for consumption crops wastewater
would be treated
to carefully calculated standards depending on risks for crop uptake
of chemical and
bacterial pollution (Bahri 1998). Innovations in inexpensive
wastewater purification
systems that extensively use aquatic plants to purify wastewater are
very promising in
this context. One example of such system is so called
Phytodepurational Activated
Sludge Systems (Bifotem @aol.com, 1999).
Another exciting area of new development is within so called urban
or peri-urban
agriculture. Urban agriculture is as old as human settlements and
cities. People have
always tried to improve their living conditions by cultivation of
crops in the vicinity
of their houses. Parallel with growth of cities, urban agriculture
is growing for better
or worse, in many cities without research, approval and control by
central
organizations. In several places urban agriculture has long
tradition and no adverse
effects on health of population were noticed. For example in
Calcutta, wetlands are
traditionally used for low-cost waste-water treatment.
Simultaneously, these wetlands
constitute highly productive multilevel aquaculture system used for
solid waste
recycling and food production with vegetables, fruit trees and fish
as outputs. In 1992
this system was first recognized by central authorities as an
ecological treatment and
bio-mass production plant, i.e. object worth protection and further
development. After
that, new wetland developments in Calcutta were initiated for the
same purpose.
Recently aid agencies (UNDP for example) and governments have begun
to realize
the potential of urban agriculture.
New development towards small-scale urban agriculture, possible to
arrange on very
limited area of a densely populated city, begun in Botswana where so
called "Sanitas
wall" has been developed. The invention is based on application of
gray water from
households for growing crops for consumption. In condition of
lacking space in urban
environment, a wall made of concrete (or sun-burned clay)
two-compartment stones
are constructed. One compartment is filled with sand and the other
with compost
where plants can grow. These bricks are put on each other to height
of about three
meters. Plants are irrigated with household's gray water. Three
meters high and about
29
3 meters long wall is enough to absorb average
volume of gray water from one
household. Figure 1 shows construction of Sanitas wall (Gunther,
1998, Winblad,
1998). Another new solution to apply in small-scale agriculture is
so called permanent
growing strips (Jarl�v 1998) see Figure 2. Instead of ploughing,
soil is ripped in
permanent strips to which rainwater is concentrated to take the
crops through drought
periods. The amount of water for irrigation is significantly lower
than in normal
agriculture. The method can give astonishing 10 to 25 times more
grain per hectare
than from traditional agriculture.
Yet another solution is to grow vegetables in concrete Bow
Benches,i.e. concrete pots
with bow shaped bottom. Scientific community of water researchers
has an important
role to play in further development of methods used in urban
agriculture including
aquaculture, pond systems, irrigation with wastewater, and newer
types of small-scale
gray water-feed agriculture in peri-urban areas. Scientists should
see the benefits of
such developments and contribute with their knowledge in order to
find safe and
efficient technical solutions. It is important to make local studies
leading to
establishment of safety rules with respect to construction, water
quality standards and
consumption restrictions. Also important is opening of new research
leading to
substitution of fossil fertilizers with nutrients that are presently
discarded as
wastewater sludge or organic solid wastes.
Real goal is then not only to recycle water and nutrients but also
all matter and,
especially, organic matter that constitutes ca 85 % of all "wastes"
produced in human
settlements. At the moment only about 5 % of solid wastes that
households generate
in the industrialized world is biologically digested to recover
nutrients. Theoretically
it is possible to use up to 85% of solid wastes as recyclable
resource (Gajdos 1995).
That brings us to think much further than just about composting or
urine separating
toilets. We begin to talk about bio-reactors that are able to
decompose not only
household wastes but also all organic refuses from all human
activities.
Microbiological processes in specially designed bio-reactors can
digest all organic
residuals and the end products will be biogas and bio-fertilizers.
In the same way as
for wastewater, the task of "solid waste management"is no longer
limited to collection
and safe disposal but more a question how to organize collection,
transportation and
recycling. In stead of problems and pollution the end products may
feed the growing
population and be a source of really clean energy. Thus, we are
beginning to talk not
only about some new isolated technologies but instead about new
total system
solutions.
Urban Water System Modeling
Optimization and simulation models are becoming increasingly
available and are used
to analyze a variety of design and operation problems involving
urban water systems.
Many are incorporated within graphic�user interfaces that facilitate
the use of the
models and the understanding and further analysis of their results.
30
Model Selection
A wide range of models is available for the simulation of
hydrodynamics and water
quality in urban systems. The selection of a particular model and
the setup of a model
schematization depends on the research question at hand, the
behavior of the system,
the available time and budget, and future use of the model. The
research question and
the behavior of the water system determine the level of detail of
the model
schematization. The time scale of the dominating processes and the
spatial
distribution of the problem are key elements in the selection of a
model, as is
illustrated in Figure and Table.
Figure shows the time scales of the driving forces and their impact
in urban water
systems. It may be wise to consider the processes with largely
different time scales
separately, rather than joining them together in one model. For
instance, the water
quality of urban surface waters is affected by combined sewer
overflows and by many
diffusive sources of pollution. A combined sewer overflow lasts
several hours and the
impact of the discharge on the oxygen concentration in the surface
water lasts for a
couple of days. The accumulation of heavy metals and organic
micro-pollutants in the
sediment takes many years and the influx of the diffusive sources of
pollution is more
or less constant in time. The impact of combined sewer overflows on
the oxygen
concentration can be studied with a detailed, deterministic
simulation model for the
hydrodynamics and the water quality processes in the surface water
system. A typical
time step in such a model is minutes; a typical length segment is
within the range
from 10 to 100 metres. The accumulation of pollutants in the
sediment can be
modeled by means of a simple mass balance. Another example is shown
in Table
13.10. In this example the wastewater collection and treatment
system in an urban
area is modeled in three different ways. In the first approach, only
the river is
modeled. The discharge of effluent from a wastewater treatment plant
is taken into
account as a boundary condition. This is a useful approach for
studying the impact of
the discharge of effluent on water quality.
In the second approach, a detailed water and mass balance is made
for an urban area.
The main routes of water and pollution are considered. Generic
measures, such as the
disconnection of impervious areas from the sewage system, can be
evaluated with this
type of model schematization. In the third, most detailed, approach,
a model
schematization is made for the entire sewage system and, eventually,
the wastewater
treatment plant.
31
Figure. Time scales of driving forces and impacts in urban
water systems.
Three methods of making a model schematization for an urban water
system.
32
Optimization
The use of the storage, transport and treatment capacity of existing
urban
infrastructure can be optimized in many cases. Optimization of urban
water systems
aims at finding the technical, environmental and financial best
solution, considering
and balancing measures in the sewage system, the wastewater
treatment plant and the
surface water system at the same time. For instance, the optimum use
of the storage
capacity in a sewage system by means of real-time control of the
pumps may
eliminate the need for a more expensive increase in treatment
capacity at the
wastewater treatment plant.
Storage of runoff from streets and roofs in surface water may be
better for river water
quality than transporting the runoff to the wastewater treatment
plant and subsequent
discharging it as effluent. Table 13.11 shows a matrix with the key
variables of
storage, transport capacity and treatment capacity in the sewage
system, the
wastewater treatment plant and the surface water. Methods for
finding optimal
solutions are becoming increasingly effective in the design and
planning of urban
infrastructure. Yet they are challenged by the complexity and
non-linearity of water
distribution networks, especially urban ones.
Numerous calibration procedures for water distribution system models
have been
developed since the 1970s. Trial and error approaches (Rahal et al.,
1980; Walski,
1983) were replaced with explicit type models (Boulos and Wood,
1990; Ormsbee
and Wood, 1986). More recently, calibration problems have been
formulated and
solved as optimization problems. Most of the approaches used so far
are either local
or global search methods. Local search gradient methods have been
used by Shamir
(1974), Lansey and Basnet (1991), Datta and Sridharan (1994), Reddy
et al. (1996),
Puma and Liggett (1992), and Liggett and Chen (1994) to solve
various steady-state
and transient model calibration problems (Datta and Sridharan, 1994;
Savic and
Walters, 1995; Greco and Del Guidice, 1999; Vitkovsky et al., 2000).
Evolutionary search algorithms are now commonly used for the design
and calibration
of various highly non-linear hydraulic models of urban systems.
They are particularly suited for search in large and complex
decision spaces, e.g. in
water treatment, storage and distribution networks. They do not need
complex
mathematical matrix inversion methods and they permit easy
incorporation of
additional calibration parameters and constraints into the
optimization process (Savic
and Walters, 1995; Vitkovsky and Simpson, 1997; Tucciarelli et al.,
1999; Vitkovsky
et al., 2000).
In addition to calibration, these evolutionary search methods have
been used
extensively to find least-cost designs of water distribution systems
(Simpson et al.,
1994; Dandy et al., 1996; Savic and Walters, 1997). Other
applications include the
development of optimal replacement strategies for water mains (Dandy
and
Engelhardt, 2001), finding the least expensive locations of water
quality monitoring
stations (Al-Zahrani and Moied, 2001), minimizing the cost of
operating water
distribution systems (Simpson et al., 1999), and identifying the
least-cost
development sequence of new water sources (Dandy and Connarty,
1995).
33
These search methods are also finding a role in
developing master or capital
improvement plans for water authorities (Murphy et al., 1996; Savic
et al., 2000). In
this role they have shown their ability to identify low-cost
solutions for highly
complex water distribution systems subject to a number of loading
conditions and a
large number of constraints. Constraints on the system include
maximum and
minimum pressures, maximum velocities in pipes, tank refill
conditions and
maximum and minimum tank levels.
As part of any planning process, water authorities need to schedule
the capital
improvements to their system over a specified planning period. These
capital
improvements could include water treatment plant upgrades or new
water sources as
well as new, duplicate or replacement pipes, tanks, pumps and
valves. This scheduling
process sewer WWTP surface water storage moderate none limited �
high transport
capacity limited � high treatment capacity none high limited
Urban Water Systems requires estimates of how water demands are
likely to grow
over time in various parts of the system. The output of a scheduling
exercise is a plan
that identifies what facilities should be built, installed or
replaced, to what capacity
and when, over the planning horizon. This plan of how much to do and
when to do it
should be updated periodically long before the end of the planning
horizon. The
application of optimization to master planning for complex urban
water infrastructure
presents a significant challenge. Using optimization methods to find
the minimum-
cost design of a system of several thousand pipes for a single
demand at a single point
in time is difficult enough on its own. The development of least
cost system designs
over a number of time periods that experience multiple increasing
demands can be
much more challenging.
Consider, for example, developing a master plan for the next twenty
years divided
into four five-year construction periods. The obvious way to model
this problem is to
include the system design variables for each of the next four
five-year periods, given
the expected demands at those times. The objective function for this
optimization
model might be to minimize the present value of all construction,
operation and
maintenance costs. As mentioned previously, this is a very large
problem that is
probably unmanageable with the current state of technology for real
water distribution
systems.
Dandy et al. (2002) have developed and applied two alternative
modeling approaches.
One approach is to find the optimal solution for the system for only
the final or
`target' year. The solution to this first optimization problem
identifies those facilities
that will need to be constructed sometime during the twenty-year
planning period. A
series of sub-problems are then optimized, one for each intermediate
planning stage,
to identify when each necessary facility should be built. For these
sub-problems, the
decisions are either to build or not to build to a predetermined
capacity. If a
component is to be built, its capacity has already been determined
in the target year
optimization.
For the second planning stage, all options selected in the first
planning stage are
locked in place and a choice is made from among the remaining
options. Therefore,
the search space is smaller for this case. A similar situation
applies for the third
planning stage. An alternative approach is to solve the first
optimization problem for
just the first planning stage. All options and all sizes are
available. The decisions
34
chosen at this time are then fixed, and all
options are considered in the next planning
stage. These options include duplication of previously selected
facilities. This pattern
is repeated until the final `target' year is reached.
Each method has its advantages and disadvantages. For the first,
`build-to-target'
method, the optimum solution is found for the `target year'. This is
not necessarily the
case for the `build-up' method. On the other hand, the build-up
method finds the
optimal solution for the first planning stage, which the
build-to-target method does
not necessarily do. As the demands in the first planning stage are
known more
precisely than those for the `target' year, this may be an
advantage.
The build-up method allows small pipes to be placed at some
locations in the first
time planning stage, if warranted, and these can be duplicated at a
later time; the
build-to-target method does not. This allows greater flexibility,
but may produce a
solution that has a higher cost in present value terms.
The results obtained by these or any other optimization methods will
depend on the
assumed growth rate in demand, the durations of the planning
intervals, the economic
discount rate if present value of costs is being minimized, and the
physical
configuration of the system under consideration. Therefore, the use
of both methods is
recommended. Their outputs, together with engineering judgment, can
be the basis for
developing an adaptive master development plan. Remember, it is only
the current
construction period's solution that should be of interest. Prior to
the end of that
period, the planning exercise can be performed again with updated
information to
obtain a better estimate of what the next period's decisions should
be.
ACUTALIZATION
Case Study 1: Storm Water Management
Ringdansen is a residential development in the south-eastern part of
the City of
Norrk�ping, which is located approximately 140km to the southwest of
Stockholm.
Two identical sets curved apartment blocks arranged in circles -
Guldringen (Gold
Ring) and Silverringen (Silver Ring) - constitute Ringdansen. Each
block has an inner
and outer circle of buildings which are of varying heights (2 to
8-storeys).
The blocks were constructed between 1970 and 1972 and belong to
Hyresbost�der i
Norrk�ping AB, a municipally owned housing company. In 1994, the
municipality
started a development programme to renovate the area. The Ringdansen
project began
in 1997 with the aim to create an ecologically sustainable
residential area with low
household consumption of energy and various recycling plans,
including rainwater. A
computer model was developed to explore the water saving potential
of the rainwater
collection scheme. This was evaluated in terms of its water saving
efficiency (WSE),
which is a measure of how much potable water has been saved in
comparison to the
overall demand.
35
Significant water saving efficiencies at Ringdansen are possible if
rainwater tanks are
included as part of a dual water supply solution, especially if low
water consumption
appliances are installed. Assuming that the whole roof area at
Ringdansen is used to
collect rainwater and rainwater is used only for toilet flushing, a
40m3 tank would
give a saving of more than 60% of the main water supply. For a low
flush washing
machine, a 40m3 rainwater tank can save almost 40% of the water
demand. The same
tank capacity would be result in a 30% saving if both toilets and
laundries are
supplied with rainwater. For each ring, it is estimated that an 80m3
rainwater tank
with a collection area of 20,000m2 would supply almost 60% of the
water needed for
irrigation of the central area during the summer months. Preliminary
results reveal
that if half the households have a car, about 60% of the water
demand for car washing
can be met using water from a dedicated rainwater system of 20m3
with a collection
area of 20,000m2. This assumes 50 litres per wash and that each car
is washed once a
month. Results from the irrigation scenario show that about 60% of
the water needed
for irrigation during the summer months could be supplied with an
80m3 tank and a
collection area of 20,000m2. In general, it was found that for a
certain roof
area/storage combination the highest WSE is reached for the smallest
population
density, while those for the default and large population densities
are practically the
same. It was also found that WSE at Ringdansen is little affected by
increases in
effective surface area for all the storage capacities. Significant
water savings can be
made with a 20m3 rainwater tank and a collection area of 20,000m2 if
low flush-
volumes appliances are installed. If, for example, only a small
portion of the whole
36
roof area is available for collecting rainwater
and local conditions only allow the
installation of the small rainwater tank, almost half of the
drinking water used for
flushing toilets and at least one fifth of the water used for
laundry can be saved on an
annual basis. If existing toilets and washing machines are retained
at Ringdansen
(standard appliances), about one third of the water needed for
flushing toilets can be
provided by rainwater, but only if a 90m3 rainwater tank is
installed. The sensitivity
of the model output to changes in individual parameters has been
determined for four
main scenarios of rainwater use: only for toilet flushing, only for
laundry, a
combination of toilet and laundry, and for irrigation. In addition,
preliminary results
were obtained for car washing. For each scenario, several
combinations of collection
area and storage capacity were modeled. A virtual Ringdansen
population was built-
up from a number of different occupancy scenarios (one to five
people for each flat)
relating to three different population densities: default, small and
large.
37
Case Study 2: Urban Water Supply: Ghaziabad City, India
National Capital Region (NCR), a unique region, is the fastest
growing region. It has the
best economic base for growth of industries and new economy as well
(software, Export
Promotion Zone (EPZ) and Special Economic Zones (SEZ)). Within NCR,
Ghaziabad is
one of the fast developing Delhi metropolitan area city. Ghaziabad
district, carved out of
Meerut district in 1976, had Ghaziabad as class I city. During
partition of India, it was a
class III town. With onset of industrialization of the surrounding
areas, it became class II
town in 1961 and with growth rate of 82.10% in 1961-1971, it
acquired the status of class
I city in 1971. After Kanpur, Ghaziabad is the biggest industrial
city in Uttar Pradesh
(U.P.) state. The city has grown at very fast pace during the last
three decades to emerge
as a Metro and strengthen its economic base. The city has one of the
best road and rail
connections among cities in U.P. State (Map 1).
The urban development of the city has been achieved through Master
Plan 1981 and
Master Plan 2001 from a population base of 70000 (1961) to 2.72
(1981) lakh and 9.68
lakh (2001), an emerging metro as per census (Map 2). River Hindon
flows through the
city dividing it into east of Hindon (Cis Hindon Area i.e. CHA) and
west of Hindon
(Trans Hindon Area i.e. THA). CHA constitutes 2/3rd in area and
population while THA
constitutes 1/3rd area and population. The proportion of the slum
population to total
population is one third.
38
39
The status of Ghaziabad was upgraded from
Municipal Board to Municipal Corporation,
known as Ghaziabad Nagar Nigam (GNN) on 31 August 1994 following
74th
Constitution Amendment Act 1992 and conformity legislation by state
government. GNN
area has been divided into four administrative zones namely City
zone, Kavi Nagar Zone,
Vijay Nagar Zone and THA Zone. The area is further divided into 60
wards.
The economy of the town has been bi-functional �
industries-cum-services since 1971.
The industrial development of the city is visible on both sides of
Hindon River. Chemical
and allied distillery (33%) dominates its industrial scene. It is
also an important centre for
trade and commerce in western U.P. sub-region. The workforce
participation ratio and
percentage workers in secondary sector are marginally declining but
the size of work
force in the city has maintained its increasing trend.
Water Supply System
Hydro-geologically, U.P. sub-region of NCR, comprising of Ghaziabad,
Meerut and
Bulandshahr districts, is a part of vast central Ganga plain, a
monotonous stretch of a low
relief plain. Ghaziabad district is very fertile and it lies in the
doab of Ganga and Yamuna
rivers. The district is bestowed with shallow and deep aquifers and
the city has been
exploiting the ground water source since last four decades. Apart
from utilizing ground
water for providing water through hand pumps in rural and
unauthorized areas, ground
water has been utilized for piped water supply since 1955, when
piped water supply
scheme was introduced.
The water supply facility, in developments carried out by Nagar
Palika and thereafter
Ghaziabad Improvement Trust, was on colony basis. From 1977, onwards
Ghaziabad
Development Authority started developing the Master Plan sectors and
with U.P.Jal
Nigam services, water supply facility continued to be provided on
sector basis without
any water supply master plan. To prepare the status and
pre-feasibility report of water
supply in Ghaziabad city, U.P.Jal Nigam, in 1995, delineated the
water supply zones for
equitable, economical and efficient distribution of water. Ghaziabad
city, under the
jurisdiction of GNN and Development Authority has been divided into
CHA having 23
Master Plan sectors which are reorganized into 19 water supply zones
(WS Zns) and 10
Master Plan sectors of THA reorganized into 10 water supply zones.
Residential areas of
the Railways, Central Government and Police Department are
considered in separate
water supply zones having their own independent water supply system
(Map 3).
40
A rosy picture of water supply in the city is projected by the water
works department of
GNN though in reality, situation is entirely different. For future
planning of resource
(water and finances) it is equally important to know the existing
situation and the
assessment of need and availability of resources. The generic issues
with regard to the
existing water supply situation at city level are:
Receding water table: ban on ground water abstraction for sale and
supply
(commercial) of water in Ghaziabad Nagar Nigam area by Central
Ground Water
Authority highlights the depleting and deteriorating ground water
conditions.
Poor quality of services: intermittent supplies of 2 to 3 hours once
a day in
specific water supply zones of THA while twice a day in remaining
water supply
zones of THA & CHA . Accompanied with supply at low pressure.
Inadequate service coverage: piped water supply covers 5% of the
abadi
population, 16% of slum population, 65% of general population
(excluding slum
population).
Weak financial position : financial position of the GNN with respect
to water
supply is not healthy as revenue collected from the service is
barely sufficient to
cover its operation and maintenance expenses; and
Sizeable investment needs: GNN can invest only 15 to 30 % of the
income from
water supply on the new projects while for substantial investment
they have to
depend on government grants and subsidy.
41
CONCLUSION
Urban water systems must include not only the reservoirs,
groundwater wells and
aqueducts that are the sources of water supplies needed to meet the
varied demands in an
urban area, but also the water treatment plants, the water
distribution systems that
transport that water, together with the pressures required, to where
the demands are
located. Once used, the now wastewater needs to be collected and
transported to where it
can be treated and discharged back into the environment. Underlying
all of this hydraulic
infrastructure and plumbing is the urban storm water drainage
system.
Well-designed and operated urban water systems are critically
important for maintaining
public health as well as for controlling the quality of the waters
into which urban runoff
are discharged. In most urban areas in developed regions, government
regulations require
designers and operators of urban water systems to meet three sets of
standards. Pressures
must be adequate for fire protection, water quality must be adequate
to protect public
health, and urban drainage of waste and storm waters must meet
effluent and receiving
water body quality standards. This requires monitoring as well as
the use of various
models for detecting leaks and predicting the impacts of alternative
urban water treatment
and distribution, collection system designs and operating,
maintenance and repair
policies.
Modeling the water and wastewater flows, pressure heads and quality
in urban water
conveyance, treatment, and distribution and collection systems is a
challenging exercise,
not only because of its hydraulic complexity, but also because of
the stochastic inputs to
and demands on the system. This chapter has attempted to provide an
overview of some
of the basic considerations used by modellers who develop
computer-based optimization
and simulation models for design and/or operation of parts of such
systems. These same
considerations should be in the minds of those who use such models
as well.
42
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