1.
Project Record
April 2016
Pollution in Mozambique
Sanitation for Better Health
Ted Sindabizera Ntwari
Erin Kelley
Josh Patterson

2. Project Record: 4/28/16
Choosing a Design
ABSTRACT
Once background information was gained about flooding in Mozambique, a list of specifications
was created as guidelines for possible design solutions. We used these specifications to create a
spec test in order to perform a quantitative analysis of our designs from our qualitative
specifications. After creating our spec test, we researched various methods and designs
previously used to deal with the problem at hand, flooding of latrines in rural Mozambique. Each
team member researched one design and made modifications to have it better meet our needs.
The designs were then run through the spec test to see which ones best fit the general regions of
interest in Mozambique. A final design, design 1, was selected and is ready for improvement.
Ways to further improve this design were also recommended to future teams.
VERSION HISTORY
Version Author(s) Date Description File Name
1 Erin Kelley
Ted Sindabizera
Ntwari
Josh Patterson
4/28/16
Latrine Designs
Goal of Study
By the end of this study we hope to have one design that will meet most of our specifications that
will fall into our cost range and will be easily built and maintained by the communities we are
focusing on in Mozambique. Along with selecting a possible design, there is also the goal of
making recommendations to upgrade this particular design to better fit the needs of the
community.
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Specs test:
In order to choose a design that would meet the desired specifications a test was created. Once all
of the specifications were proposed, they were give a rank of one to three, with three being the
most important specification. This gave each spec a weight of importance. Next, each design
was examined in detail and each person ranked the design on how well that specific design met
that specification by giving the design a number on a scale of 1­10, with 10 being the design met
that particular specification extremely well. Once each design had a number for each spec,
individuals specs were multiplied by their weight of importance and then summed together to
give each design a total score. The higher the score, the better the design fit our specifications.
Specs
● Cost < $100
● Water resistant­ limiting water pollution
● Ventilated­ prevents smells
● Offers Privacy­ Can be used without being noticed.
● Handicap accessible­ accesible to all members of the community
● Reusable­ can be emptied and used again after pit is filled
● Height of latrine compared to water level (can be above ground)­ at least 3 meters above
highest point of the water table.
● Limits flies­ helps prevent spread of disease
● Aesthetics­ Should be semi­appealing so the community accepts it.
● Container size­ The size of the container collecting the waste should be .5m^3 (around
4 months)
● Resistant to collapsing­ Due to water causing the soil to shift.
● Community lead sanitation­ meaning that the community could build it, up keep it, and
they will take ownership of the latrine.
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4. Project Record: 4/28/16
Design 1:
Our first design is a reusable, dual container
latrine with urine separation. We used the design shown
in the diagram. The base would be 2x1 m and stand
1.5m tall and made from concrete. There would be two
used 55 gal oil drums contained within the base. Each
of these containers can hold the waste produced by a
family of 8 in four months. There would only be 3 walls
and one support beam on the side without a solid wall
for the base. Instead of having a wall on one side there
would be a support beam in the middle and the rest
would be open, this allows access to the drums so they
can be emptied. This open space would be covered by a tarp. The upper shelter would be made
out of local lumber such as bamboo to limit cost as well as make it easier to access. The latrine
slab will have two drop holes with a single urine collecting groove located between the two drop
holes. The base will have the dimensions for length, width, and height of 2m x 1m x 1.5m
respectively.
One problem that needs to be addressed with this design is maintaining the waste. For
solid waste to compost properly it needs to be agitated, usually through turning. This design
would need to be modified to include a crank or some other method of agitation. Another
problem is that it is not easily handicapped accessible due to it being raised off the ground. With
flash flooding the ability of the base to withstand impact could also be a concern. If there is a
flash flood the structure must be able to withstand impact from the water as well as any debriegh
being forced against it.
We put the design through our spec test to see how viable it would be for a flood prone
area in Mozambique. This test gives a numerical value to each of our specifications so we can
have a quantitative analysis for each of our designs. This test would be more accurate and useful
if we could refine it for a specific client and area, but as it is now it gives us a rough estimate of
how practical our designs would be for the general area. This design received a 215.5 on our
spec test, which is the highest score for any of our designs.
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Materials used:
● Concrete
● Rebar
● 55 gal drum
● Tarp
● Bamboo
Cost:
● Reused poly 55 gal drums: 2x$14= $28
● 75 m of Rebar = $5
● .64 m^3 concrete= $67
● tarp= $5
● Bamboo: Negligible
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Design 2:
The second design that was investigated was the Urine Diverting Dry Toilet or UDDT. The main
idea of this is to separate the urine from the feces. The benefit of this is that the storage container
will take longer to reach its maximum
capacity and will have to be emptied less
often. Due to the fact that the solid waste
needs to decompose for a longer time period
than the urine, the feces can be stored for six
months while the urine can be used 2 months
after or filtered into the ground away from
wells and other water supplies. The UDDT
consists of a specially designed toilet with a
front section for urine and the rear section is
where the feces are deposited. The urine is
then drained into some sort of plastic
container such as a gas can. One idea we had
for the feces collection container is to use an
old 55 gallon oil drums. In the article this
community used woven wooden baskets
with burlap bags to collect the waste. If the
oil drums are used we calculated that they
will last a family of eight for around four
months. When one drum is filled it can be
replaced with a second one. The first one
will then be moved and mostly sealed with maybe a few air holes in the top to allow for faster
treatment. After six months the feces can be used as fertilizer. The urine needs to sit for around
3­4 months and then it can also be used in gardens. The wooden shed providing privacy for the
user can be constructed out of local materials such as bamboo which if it is very common in the
area could possibly be free. In the cost estimate below the price of wood from Lowes was used,
however to save on cost, local woods should be used. The dimensions of the structure are around
4ft x 4ft x 8ft. Below several technical engineering drawings needed for construct are displayed.
Modifications to these drawings will need to be made in order to allow space to place the oil
drums beneath the structure. Another idea had come up as a modification to the oil drums that
allowed for a faster treatment process was to add some sort of crank.
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Cost estimate for the UDDT
It is important to note that the following cost estimate is in fact just an estimate. Some of
the materials were estimated from data given in 2010. The wood estimate was for spruce pine
from Lowes which will most likely be more expensive than local woods found in Mozambique.
Design strengths
­ Above the ground so we do not need to worry about the soil crushing our container
­ Separates waste into two different containers allowing for fertilization with the urine to
take place sooner than fertilization with feces.
­ Will not fill up as quickly due to separation of urine and feces.
­ Made fairly cheaply
­ Offers privacy for users
­ Can be constructed by community
­ Doesn’t need to be emptied weekly
­ Community accepted
Design Weaknesses
­ Users must climb to a raised bathroom which will draw attention
­ Needs to be modified to make it accessible to the handicapped
­ Will need to switch out the containers every four months which will not be enough time
to treat the other full container
­ Base not as stable when wood is used instead of concrete
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Design 3
I. Design description
This design is entirely above ground. It consists of two concrete rings placed one next to each
other (see dimension sheet) a meter high each to serve as waste containers within one entire
chamber. The rings have a volume of 0.58 meters cubed each, which implies that each one can
hold the waste for about 6 months for an 8 member family. Each compartment is jointed with a
slab foundation by sealing. the sealing is done with cement and sand. This is a crucial part of the
design as this will prevent buoyancy of the rings in a case of flooding, thus preventing the waste
from seeping out.
Figure 1.1
The chamber (or base of the structure) enclosing the two rings is fenced all around with
non­porous concrete preferably in order to prevent water from rainfall to enter the chamber in a
case of flooding.
The design also comprises of 2 holes for defecation each vertically aligned with the rings and a
hole for urine collection connected to a urine diverting pipe that drives the urine to a urine pot
outside the chamber. The slope of this pipe should be at least 2% downward­oriented to avoid
precipitation of phosphate into the pipe, thus causing clogging. For a urine drainage system, the
urine contained in the urine pot can be drained on a regular basis by leaching. For the purpose of
emptying the feces, a circular section with a diameter of the rings (3’) will be partially cut out
around each defecation hole in such a way that a piece of concrete is easily opened and closed,
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allowing to reach the plastic bags containing the waste in the rings.
Another feature attached to the base of the structure would be a 2’x2’x2’ traditional sink made of
aluminum. Note that this feature is not considered in the current. It would only be considered
upon request of whichever community ends up being the project’s client.
The upper structure of the design will be made out of bamboo poles. This includes the front,
back and side covers as well as the roof. The reason for that is that this type of material is freely
obtained in Mozambique. The poles are of a 2.5’’ diameter. The ideal setup would be to have
them vertically embedded into concrete when it is still liquefied. Consideration will be given to
capping the bottom end of each pole so that in case of flooding, water will be prevented from
penetrating concrete and entering in each pole causing rotting. For underground construction, the
type of concrete used will have to resist the ingress of moisture and aggressive species from the
soil.
The design will also have two ventilation pipes starting from the waste containers and extending
3 feet away from the roof. A screen should be placed on top of each pipe to prevent flies from
reaching the waste containers thus causing diseases in the community.
The following figures represent the finished design as well as engineering drawings detailed
dimensions.
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II. Materials used
● Feces chamber (concrete)
● Rings (concrete)
● Slab foundation (concrete)
● Urine diverting pipe (PVC)
● Urine pot (plastic)
● Ventilation pipe (PVC)
● Upper structure (Bamboo poles)
III. Cost analysis
● 150 kg (cement +sand+brick)= $93.30
● Vent pipe=$3.83
● Urine diverting pipe =40 cents
● Urine pot= $2.05
● Bamboo poles = $0.00
Total cost =$99.58
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IV. Advantages of the design
­ Cost < $100.
­ Structurally stable.
­ Well Ventilated.
­ Comprises of a screen on top of the vent pipe, which limits flies.
­ Follows the recommended volume of the feces vault.
­ Overall design not too complex for a community to build​.
­ The waste containers are made out of concrete. They are structurally stable. Therefore,
there are no issues with buoyancy potentially leading to contamination in a case of severe
flooding.
­ The joint of the slab foundation and rings is sealed with cement and sand, which prevents
leakage at the bottom, thus contamination.
­ Usage of Bamboo poles as covers for the upper structure, significantly minimizes the
overall cost of the design.
­ Because of the structural stability of the base, the ramp is lowered from a regular ramp of
a mounted latrine. This will offer a better privacy handicap accessibility.
V. Inconveniences of the design
­ Emptying the waste by pulling plastic bags from the filled ring will be burdensome
considering that the waste will have been deposited for 6 months.
­ Since the ramp of the latrine is lower than the maximum height of the water tables in a
case of flooding (2m), the entire base of the structure will be submerged impending usage
of the latrine for a certain amount of time.
­ Bamboo poles are preferable food resources for termites. Therefore, an extra layer of
coating (wood preferably) has to be considered which increases the total cost.
­ Having the poles embedded into concrete can cause tipping of the entire upper structure
about the point of contact between the bottom end of each pole and top of the base in case
severe flooding.
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Conclusion
Now that each design has been examined in depth and run through our spect test, we can now
choose design #1 as our final choice. It scored the highest on the spec test and will hopefully be a
good fit for flooding areas in rural Mozambique. Like any design there is always room for
improvement and modification. Making the system handicapped accessible would be one
addition that would be important to make in order to ensure that everyone in the community or
home would be able to use it. Another modification would be to reinforce the base to help limit
damage from impacts from debris and flooding. Our thinking behind this modification is that
concrete, even though it provides a very stable base is not completely indestructible. Further
research should be done to find ways to make sure the concrete base will hold up against debris
smacking into the walls during a flood. Another thing to look into would be a wash station for
cleaning after people are done doing their business. This station should be kept inside the up
structure for privacy. A further investigation into design improvements would be the next
recommended step in this project toward helping communities in rural Mozambique. Having a
specific client and area would also help us refine this design to best suite the needs of that
particular community.
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References
D. Hurtado, “Compost Latrines in Rural Panama: Design, Construction and Evaluation of
Pathogen Removal,” pp. 1–81, 2005.
“Hydraulic Performance Assessment after Water Management Reforms,” ​A Tradition in
Transition, Water Management Reforms and Indigenous Spate Irrigation Systems in Eritrea
PhD, UNESCO­IHE Institute for Water Education, Delft, The Netherlands, pp. 101–112, 2007
R. Gensch, A. Miso, G. Itchon, and E. Sayre, “Low­Cost Sustainable Sanitation Solutions for
Mindanao and the Philippines,” 2010.
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