This course will examine current conditions and trends in water and sanitation services in low and middle income countries. Within it we will take a critical look at the underlying political, economic, social, and technical reasons why almost a billion people lack access to improved water supplies and almost 2 billion still do not have improved sanitation services.
Video 3.4: Condominial sewers, desalination
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來自 University of Manchester 的課程
发展中国家的水供应和卫生政策
58 個評分
從本節課中
Supply-Side Costs of Water and Sanitation Services
與講師見面
Prof Dale WhittingtonProfessor
Manchester Business School
Dr Duncan ThomasLecturer
Alliance Manchester Business School
In this video, I want to briefly discuss two technologies and
say a few things about their costs.
The first is condiminial sewers.
The second is desalinization.
Condominial sewers are a different low cost way to design sewer systems.
They incorporate the design and community planning insights of an innovative
Brazilian engineer, Jose Carlos Melo.
There are three main ways that condominial sewers lower costs
compared to traditional sewer systems.
First, they use smaller diameter sewer pipe.
Second, they use lower gradients that are not constructed deep under streets.
Traditional sewer lines have to be laid deep to protect them from pounding by
traffic.
Third, condominial sewer designs save on the length of pipe needed.
This slide shows three different condominial sewer designs.
On the left is a backyard design.
Here the small diameter lines are laid in sequence through the backyards of
house plots.
This design substantially reduces the length of sewer line required.
The disadvantage of this design is that if the sewer becomes blocked by the actions
of a downstream neighbor, the sewage backs up into the yards and
homes of the upstream houses.
More community organization and
planning are needed to address such collective action problems.
The middle design in this slide shows the condominial branch going through the front
yards of the houses.
The design on the right panel on this slide shows the condominial sewer line
laid under the sidewalk in front of the house.
Both the front yard and the sidewalk designs in the middle and
right panel use more sewer line than the backyard system, but
they still save money compared to traditional sewer systems.
This is because they do not have to be protected from heavy traffic and
because they use small bore or small diameter pipe.
This photograph clearly shows the size
of the small diameter sewer pipe used in neighborhood condominial systems.
Notice that it is not hard to handle by hand.
This means that it is possible for
communities to contribute labor to the construction of the condominial system.
This further reduces financing requirements.
This next photograph shows a hand dug trench for a condominial sewer line.
Notice how close the trench is to the houses.
This is another advantage of the condominial system.
The network design can be adapted for use in unplanned,
irregularly laid out neighborhoods much easier than a traditional sewer system.
This next photograph shows the location of a condominial sewer line in
the front of houses near a sidewalk.
This next slide shows a financial comparison of the cost
of a connection to a traditional sewer system and
to a condominial system in selected communities in Latin America.
The connection to a traditional system is estimated to cost about 276 USD,
compared to 142 USD for connection to a condominial system.
This next slide shows a cost comparison between a connection to a traditional
sewer system into a condominial system at another location.
You'll note that for this case,
a connection to both types of systems is substantially cheaper.
In this example, the condominial system is still cheaper, about 40%,
than the traditional system.
A good rule of thumb is that a connection to a condominial system is about 40 to 50%
cheaper than a connection to a traditional system.
Notice that although this is a very substantial cost reduction,
it is a reduction in only one of the seven cost components we discussed previously.
Also, at least for backyard designs,
the service provided by a condominial system may not be quite as convenient.
Now let's discuss desalinization technology.
Just a personal note before we begin, when I was a child, for a short time,
my father was a co-owner of a small bottled water company.
The company used thermal or
evaporation distillation techniques to produce distilled water.
My father always used the term desalinization, another is desalination.
I'm afraid desalinization is embedded in my brain, and I'll use it here.
The important thing for you to know about desalinization technology is
that the costs have fallen significantly over the last two decades.
And increasingly, it is a feasible, although still expensive,
raw water supply option.
Desalinization is now widely used around the world.
There are about 50 million cubic meters of production in operation.
Almost half of the global desalinization production is in the Middle East.
North America, Europe, and Asia each have about 15% of global production capacity.
There are two main desalinization technologies.
The old technology is thermal or evaporation.
The newer technology is membrane or reverse osmosis.
Most new desalinization capacity uses advanced membrane technology.
Membrane units are now available in many sizes or
capacities from very small to very large.
Small units are about the size of a small automobile,
large units are the size of a factory or a department store.
An important fact about desalinization technology that
you may not have thought about is that it is not just for coastal communities,
there is saline brackish water in many places that could be desalinized.
For example, saline ground water can be an input to a desalinization plant.
Costs have fallen to as low as $0.50 US per cubic meter for
seawater desalinization.
The costs depend on the salt concentration of the intake water and energy costs.
One big advantage of desalinization technology is the capacity can be
added incrementally at approximately the cost of previous capacity.
Another important aspect of the economics of desalinization is that it may have
added value as a way of diversifying a portfolio of raw water sources.
This diversification value is likely to be especially important when the reliability
or security of a city's other raw water sources are uncertain.
This slide shows a breakdown of the relative size of different components of
the total annual cost of a desalinization facility.
As shown, capital and energy are the two biggest cost components.
Together they constitute about 78% of the total annual cost.
These are very capital intensive and energy intensive facilities.
Note how small the labor contribution is to the total annual cost, just 4%.
In addition to the high energy use of desalinization facilities,
there are several associated environmental concerns.
The first is that the production process leaves a residual wastewater with a high
brine concentration.
This should be disposed of safely.
How big a disposal problem this is depends on where the desalinization facility is
located.
The second environmental concern is entrapment of sensitive marine organisms
in the plant intake.
Adverse environmental consequences can be reduced if care is taken with
the placement of the intake.
Third, reverse osmosis does leave some residuals in the output water that may
require additional treatment.
Just as an aside, it is fascinating to actually visit a desalination facility.
If you have a chance to do so, don't pass it up.
To wrap up, we often tend to think of water and
sanitation technologies as static.
And it is true that many have been around for a long time.
But condominial sewers and desalinization with membrane technology
remind us that important technological innovations are occurring in the water and
sanitation sector.
The important message here is that we need to be on the look out for
technological innovations.
Some of these innovations relate to policy interventions that have been designed and
implemented to change baseline conditions, but
others are best conceptualized as part of the dynamic baseline.
Such innovations were not in fact designed to change water and sanitation conditions.
They were occurring anyway.
But once they became widely available,
they have an important spill over effect on the water and sanitation sector.
For instance, condominial sewers were a policy intervention intended for
use in the water and sanitation sector.
On the other hand, there are developments, such as cell phones,
that enable households to pay their water bills electronically.
This is an innovation from other sectors that was not originally intended for
use in the water and sanitation sector, but has now spilled over.
