Attachment G-1: Pit Latrine Diagram
Fig E.1a: Pit Latrine
Fig E.1b: Plan View of Twin Pits
Fig E.1c: Section of a water-sealed pan
Fig E.1d: 3D view of Overflow Pipe
Fig E.1e: 2D view of Overflow Pipe
Attachment G-2: Composting Latrine Diagram
Fig E.2a: Compost Toilet
Fig E.2b: Dimensions of vault
Attachment G-3: Pros and Cons of Pit Latrine and Composting Latrine
Pit Latrine
Advantages
1. Convenient Æ pour flush, no odor
2. Hygienic during emptying
3. Emptying done every 3 years
4. Minimal maintenance
Disadvantages
1. Needs water
2. Emptying takes effort
3. Soil must be permeable
Composting Latrine
Advantages
1. Soil need not be permeable
2. Vault is above the ground,
emptying is very easy
3. Waste product can be used as
fertilizer
Disadvantages
1. More costly to build the vault above the
ground ($ 544.2 vs $ 140 for pit latrine)
2. Empty more often than pit latrine (once a
year)
3. Takes up a lot of space
4. High maintenance Æ add sawdust,
woodchip, ashes, etc
5. Problems with odor and insects
Attachment G-4: Exact Pit Calculation for Pit Latrine
Pit
Volume of discharge = 0.05 m3/ person/ year 1
Size of one household = 9 persons
Number of years before emptying = 3 years
Volume for 9 persons for 3 years=(0.05 m3/ person/ year)*(9 persons)*(3 years)=1.35 m3
Pit area = (1.25 m) * (1.25 m) = 1.56 m2
Depth = Volume / Area = (1.35 m3)/ (1.56 m2) = 0.87 m
The depth of the pit should be designed 0.20 m deeper from the surface to prevent wastes
from coming too near to the surface after the designated time.
Thus, Pit Depth = 0.87 m + 0.20 m = 1.07 m = 1.1 m
In summary, the pit dimension is 1.25 m long * 1.25 m wide * 1.1 m deep
Pit Cover
The pit cover should extend 12 cm from each side of the pit. Thus:
Length = length of pit + 2 * (0.12 m) = 1.25 m + 0.24 m = 1.49 m2
Width = width of pit + 2 * (0.12 m) = 1.25 m + 0.24 m = 1.49 m2
Thickness of pit cover = 6 cm = 0.06 m
Thus, volume of pit cover = (1.49 m) * (1.49 m) * (0.06 m) = 0.133 m3
Cover Base
The cover base should extend 10 cm from each side of pit. Thus:
Area of cover base = (1.25 m + 0.10 m) * (0.10 m) * 4 = 0.54 m2
Thickness of cover base = 2 cm = 0.02 m
Thus, volume of cover base = (0.54 m2)* (0.02 m) = 0.0108 m3
Slab
Area of slab = (1.0 m) * (1.2 m) = 1.2 m2
Thickness = 2 cm = 0.02 m
Thus, volume of slab = (1.2 m) * (0.02 m) = 0.024 m2
1
Taken from Lifewater International website: 0.04 m3/ person/ year. We add 0.01 m3 factor of safety
http://lifewater.org/resources/san1/san1d2.pdf (March 2006)
Shelter
Area of shelter base = (1.0 m) * (1.2 m) = 1.2 m2
Height = 1.8 m
Area of shelter wall = 2 * (1.0 m) * (1.8 m) + 2 * (1.2 m) * (1.8 m) = 7.92 m2
The area of the roof extends 0.12 m from each side of the shelter
Area of roof = (Length of shelter + 0.12 m) * (Width of shelter + 0.12 m) = (1.2 m + 0.12
m) * (1.0 m + 0.12 m) = 1.48 m2
Attachment G-5: Calculation for Composting Latrine
Vault
Volume of discharge = 0.06 m3/ person/ year 1
Size of one household = 9 persons
Number of years before emptying = 1 year
Volume for 9 persons for 2 year = (0.06 m3/ person/ year)*(9 persons)*(1 year) = 0.54 m3
Since for composting toilet, the two vaults are side by side, thus we do calculations for
total volumes of both vaults instead of individual vault.
Volume for 2 vaults = (0.54 m3) * 2 = 1.08 m3
Vault area = (1.10 m) * (1.60 m) = 1.76 m2
Height = Volume / Area = (1.08 m3)/ (1.76 m2) = 0.61 m
For composting latrine, we allow an additional 0.10 m height of vault to prevent wastes
from coming to close to the surface after the designated time.
Thus, vault height = 0.61 m + 0.10 m = 0.71 m = 0.70 m
In summary, the vault dimension is (1.10 m long) * (1.60 m wide) * (0.70 m high)
Thickness of vault wall is 75 mm and thickness of divider between the two vaults is 100
mm
Total area of vault wall = 0.075 m * (2 * (2*0.80 m + 0.075 m + 0.10 m) + 2 * (1.10 m +
0.075 m) = 7.25 m2
Total volume of vault wall = (7.25 m2) * (0.70 m) = 5.08 m3
1
Taken from Lifewater International website: 0.06 m3/ person/ year. http://lifewater.org/resources/san1/san1d2.pdf
(March 2006)
Slab
Slab length = length of vault + 2*0.075 m + 0.10 m = 1.60 m + 0.15 m + 0.10 m = 1.85 m
Slab width = width of vault + 2*0.075 m = 1.10 m + 0.15 m = 1.25 m
Thickness of slab = 10 cm = 0.10 m
Thus, volume of slab = 1.85 m * 1.25 m * 0.10 m = 0.231 m3
Attachment G-6: Comparison between different materials
Materials Unit Cost
Material
Cement
Wood
Gravel
Sand
Brick
Chicken wires
Zinc Sheet
8 inch PVC
Toilet Seat
Hammer
Saw
Labour
Lock
Hinges
Nails
Wire netting
Unit
25 kg
m2
m3
unit
m2
m2
m
unit
unit
unit
day
Unit Cost
5.3
4.5
40
0.04
2
5
3
20
2
5
7
2
2
1
2
Reference
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
Data collected from previous visit (August 2005)
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
Data collected from previous visit (August 2005)
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
FUCOHSO latest information (February 2006)
Data collected from previous visit (August 2005)
Data collected from previous visit (August 2005)
Data collected from previous visit (August 2005)
Data collected from previous visit (August 2005)
Data collected from previous visit (August 2005)
Table G.6a: Materials unit cost
Different materials are used to build vault, slab and shelter
Vault can be made out of concrete, brick or ferro-cement
Slab can be made out of concrete, ferro-cement, or wood
Shelter can be made out of concrete, brick, ferro-cement or wood
We use the construction of the shelter to compare the cost of different materials
Area of shelter base = 1.0 m * 1.2 m = 1.2 m2
Height = 1.8 m
Area of shelter wall = 2 * 1.0 m * 1.8 m + 2 * 1.2 m * 1.8 m = 7.92 m2
Area of shelter wall minus door = 7.92 m2 – 1.0 m * 1.8 m = 6.12 m2
Using concrete, the thickness of the wall can be 10 cm = 0.10 m
Thus, volume of concrete used = 6.12 m2 * 0.10 m = 0.612 m3
Concrete is a mixture of 1 part cement to 3 parts sand to 4 parts gravel
Total volume of concrete used = 0.612 m3
Volume of wet cement = 1/ (1 + 3 + 4) * 0.612 m3= 0.0765 m3
Volume of dry cement = 0.0765 m3 * 1.65 = 0.126 m3
Weight of 0.0692 m3 = 0.126 m3 * 50 kg / 0.0322 m3 = 196 kg
Cost of cement = 196 kg/ 25 kg * $ 5.3 = $ 42
Volume of gravel = 4/ 8 * 0.612 m3 = 0.306 m3
Cost of gravel = 0.306 m3 * $ 40 = $12.24
Total cost of concrete = $ 42 + $ 12.24 = $ 54.24
Using brick:
Dimension of brick: 40 cm * 20 cm
Area of one brick = 0.04 m * 0.02 m = 0.0008 m2
No of brick needed = 6.12 m2/ 0.0008 m2 = 7650
Total cost of brick = 7650 * $ 0.04 = $ 306
Using ferro-cement, the thickness of the wall can be 5.0 cm = 0.05 m
Thus, volume of ferro-cement used = 6.12 m2 * 0.05 m = 0.306 m3
Ferro-cement is a mixture of 1 part cement to 3 parts sand
Total volume of ferro-cement used = 0.306 m3
Volume of wet cement = 1/ (1 + 3 + 4) * 0.306 m3= 0.0383 m3
Volume of dry cement = 0.0383 m3 * 1.65 = 0.0631 m3
Weight of 0.0692 m3 = 0.0631 m3 * 50 kg / 0.0322 m3 = 98 kg
Cost = 98 kg/ 25 kg * $ 5.3 = $ 20.8
Cost of chicken wire = 6.12 m2 * $ 2/ m2 = $ 12.24
Total cost of ferro-cement = $ 20.8 + $ 12.24 = $ 33.04
Using wood:
Cost of wood = 6.12 m2 * $ 4.5 = $ 27.54
Material Comparison Table:
Material
Concrete
Brick
Ferro-cement
Wood
Cost
$54
$306
$33
$27
Lifetime/ years
40
50
20
5
Strength
good
good
good
poor
Attachment G-7: Family size of each household
No of people
9
2
2
1
4
8
6
5
7
6
8
6
7
5
6
3
4
3
1
No of families vs Family size
6
5
No of families
No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
4
Series2
3
2
1
0
1
2
3
4
5
Family size
7
4
7
7
4
6
1
5
3
4
Total number of families (not including isolated house) = 29
Total number of people = 141
Average family size = 4.87
6
7
8
9
Attachment G-8: Materials Cost
Material
Cement
Wood
Gravel
Sand
Chicken wires
Zinc Sheet
Unit
25 kg
m2
m3
m2
m2
Unit Cost/ $
5.3
4.5
40
2
5
Refer to Table G.6a for thorough unit cost and cost reference
Cost for Pit Latrine
The cost listed below is based on using ferro-cement for pit cover, cover base and slab
and wood for shelter.
•
•
•
Ferro-cement uses 1 part cement and 3 part sand.
Wet volume is the final volume of cement and dry volume is the volume of ferrocement when it is not yet mixed with water. Dry volume is 1.65 * Wet volume1.
0.322 m3 of dry cement weigh 50 kg
Total volume of ferro-cement used (pit cover, cover base, slab) = 0.024 m2 + 0.0108 m3 +
0.133 m3 = 0.1678 m3
Volume of wet cement = 1/ (1 + 3) * 0.1678 m3 = 0.04195 m3
Volume of dry cement = 0.04195 m3 * 1.65 = 0.0692 m3
Weight of 0.0692 m3 = 0.0692 m3 * 50 kg / 0.0322 m3 (1) = 107 kg
Material
Cement
Wood
Unit
25 kg
m2
Gravel
m3
Sand
Chicken wires
Zinc Sheet
8 inch PVC
Toilet Seat
Labour
Lock
Hinges
Nails
Wire netting
m2
m2
m
unit
day
Unit Cost
5.3
4.5
Quantity
107 kg
7.5
Cost/ $
23
34
40
-
-
2
5
3
2
1.8
5
-
7
2
2
1
2
4
Total Cost
4
9
15
20
28
2
2
1
2
140
Cost of entire project = $ 140 * 29 = $ 4060
1
Taken from Lifewater website: http://www.lifewater.ca/Appendix_J.htm (March 2006)
Cost for Composting Latrine
The cost listed below uses concrete for vault and slab and wood for shelter.
•
•
•
Concrete uses 1 part cement, 3 parts sand and 4 parts gravel.
Wet volume is the final volume of cement and dry volume is the volume of
cement when it is not yet mixed with water. Dry volume is 1.65 * Wet volume1.
0.322 m3 of cement weigh 50 kg
Total volume of concrete used = 5.08 m + 0.231 m = 5.31 m3
Volume of wet cement = 1/ (1 + 3 + 4) * 5.31 m3 = 0.664 m3
Volume of dry cement = 0.664 m3 * 1.65 = 1.10 m3
Weight of 0.0692 m3 = 1.10 m3 * 50 kg / 0.0322 m3 (1) = 1700 kg
Volume of gravel used = 4/ 8 * 5.31 m3 = 2.67 m3
Material
Cement
Wood
Gravel
Unit
25 kg
m2
m3
Unit Cost
5.3
4.5
40
Sand
-
-
Chicken wires
Zinc Sheet
m2
m2
-
8 inch PVC
m
-
Toilet Seat
Labour
Lock
Hinge
Nails
Wire netting
unit
day
-
Quantity
1700 kg
7.5
2.66
-
-
5
Cost/ $
360
34
106.2
1.8
-
-
7
2
1
1
2
4
1
2
1
1
Total Cost
9
28
2
2
1
2
544.2
Cost of entire project = $ 544.2 * 29 = $ 15781.8
1
Taken from Lifewater website: http://www.lifewater.ca/Appendix_J.htm (March 2006)
Attachment G-9: Details of Technological Innovation
A. Pit Alarm System
The diagram above shows a mechanical pit alarm system. The detachable pipe allows
detection of solid waste a few months before the pit gets filled up. User will find water
being flushed down slower than usual. And this is the indicator that the pit is almost full
and it is not long till he/ she has to change the pit used.
The second pit alarm system is more electronical. It relies on a voltage source, which can
be solar powered battery. Once the solid reaches a certain height, there will be a layer of
water on top of it. Water is a conductor of electricity, and it will close the circuit, lighting
the light bulb, which will alert the user that it is time to empty the pit.
Another alternative is to use chemical properties of the solid waste to generate small
current, which will light up the light bulb. Research will be done on the area of
electrochemical cell and chemistry content of the excreta to look into this possibility.
B. Cost Saving Shelter
Generally a shelter is designed with ventilation on top. This is an extension to that idea.
By making the ventilation bigger, while at the same time making sure that the angle of
the netting is such that nobody can look to the level of the toilet seat, privacy and cost
saving can be achieved at the same time. This is assuming that the cost of netting is much
cheaper than the material wall. The design will be most effective if brick is used for
shelter wall since a reduction of a few more bricks mean a lot of cost saving.
C. Pit Emptying Tool
The pit emptying tool works with leg muscles, since it is stronger than arm muscle. The
main two components are the wheel and the sliding mechanism. The function of the
sliding mechanism is to lift the whole ploughing tool up when it hits the ground, thus
allowing continuous motion. The earth will be collected at one site.
Another design for the tool is shown below:
A bucket is added to collect the earth.
Attachment G-10: Specific Soil Tests
The two soil tests that need to be carried out in our next trip are the test for groundwater
level and percolation test, which is a test for the permeability of the soil.
Test for Groundwater Level
The depth of the pit is to be 1 m above the groundwater level. Our design pit depth is 1.1
m. Thus the groundwater level should be at least 2.1 m deep.
Procedure:
1. Dig a hole 2.5 m deep
2. Wait for two hours for the groundwater to enter the hole
3. Check for the depth of the water level inside the hole. This can be done by
disturbing the water with a stick, or a stone tied on a string and note the length of
the stick or string inside the hole
4. If the water level is more than 2.1 m deep, the site is suitable for pit construction
5. The test should be carried out during the wettest season of the year
Percolation Test
1. Two percolation tests must be conducted at the proposed site. Two test holes are
dug to the depth of the pit (1.1 m). Generally, the results of the two tests will be
about the same. If they differ, use the slower of the two percolation rates to design
the system.
2. Dig or bore a hole about 300mm in diameter, or 300mm square, to the proper
depth. Do not use the same hole used for locating groundwater. Make the walls of
the hole vertical. Scrape the walls to remove any patches of compacted soil. Place
about 50mm of clean gravel in the bottom of the hole.
3. Fill the hole with water and let it soak overnight. This will allow ample time for
soil swelling and saturation, and provide more accurate test results.
4. Place a board or piece of lumber across the center of the hole and anchor it firmly
in place, perhaps by placing a rock on each end. The board must not be moved
until the test is complete. Mark a point near the center of the board to be used as a
guide for the remainder of the test.
5. Most or all of the water poured in the day before will have drained away. Pour in
enough water so that the depth is 200mm.
6. Place a pointed slat or similar measuring stick next to the reference mark on the
board and slide it down until it just touches the water surface. Ripples on the
water can be observed when the slat touches. Note the exact time and draw a
horizontal line on the slat, using the edge of the board for a guide, as shown in
Figure 2.
7. Repeat step 6 at l0-minute intervals. If the water level drops rapidly, repeat at oneminute intervals. Do not allow the water to drop lower than 100mm. If it does,
pour in more water to the 200mm depth and continue the test.
8. Note the spacing between the pencil marks on the slat. When at least three spaces
become approximately equal, as shown in Figure 3, the test is completed. This
may take as little as one-half hour or as long as several hours.
9. Using the measuring tape or ruler, measure the space between the equal pencil
markings and compute how long it took the water level to drop 25mm. This step
is necessary because percolation rates are described in terms of "minutes per
25mm." This can be approximated closely with the ruler and a series of equally
spaced markings on the slat, as shown in Figure 3, or it can be calculated.
10. If the percolation rate for 25mm isbetween 10 and 60 minutes, the soil is
acceptable.
Attachment G-11: Site layout