Latrines
Pit Latrine
Latrines, and especially pit latrines, are the most commor and simple sanitation systems. A pit latrine is practical for rural areas because it is the cheapest possible system and the easiest to build.
One major problem with pit latrines is the limited capacity: only a certain number of people can use the latrine, or else it becomes full too quickly and another pit must be dug. Another problem is that the latrine, if it is improperly made or made in the wrong place, can contaminate nearby wells or surface water. Also, if the ground water level is near the surface it may not be possible to dig a deep pit.
CAPACITY
The volume of the pit may be planned by using the rough figure of at least 0,06 cubic meters per person per year. Thus a pit which is 1 m square and 3 m deep may serve a family of five for about 6 years, before it becomes two-thirds full and a new pit has to be dug.
Pit latrines of the type shown on here (Figs. 1 & 2) should not be used by large numbers of people unless there is space available to dig several pits. If many people use the same pit it will quickly become full, and the ground around It can become contaminated.
It is a good idea to dig two pits at once, so that when one is 2/3rds full it can be closed, filled to the top with soil, and left there for 6 month3 to a year; by which time the harmful, disease-causing organisms in it will have been destroyed. The slv.dge can be taken out and mixed with compost, making a very valuable (and non-imported) fertilizer for gardens or farms.
- NOTE: Human wastes which have not been composted for at least 6 months should never be used as a fertilizer for food crops, because disease can be spread that way.
LOCATION
The pit latrine should be located at least 6 m away from any house, and at least 30 m away from any water source: well, bore hole or stream. The latrine should never be located uphill from a water source, this if extremely Important.
DESIGN AND CONSTRUCTION OF THE SQUATTING SLAB
The squatting slab should be designed with easy cleaning in mind. It is made out of concrete reinforced by iron rods as shown in Fig. 1. The rods should be about 8 mm in diameter.
The slab may be square, round, or rectangular in shape. A common size is 100 by 100 cm. The whole slab will weigh about 140 kg. The advantage of a round slab is that it can easily be rolled around the site and into place. The slab should be about 7 cm thick. The raised foot rests make the slab easier to clean. The shape of the hole and foot rests may vary; a typical arrangement is shown here. The hole should be at least 36 cm long to prevent soiling of the slab, and less than 18 cm wide so that small children can't fall through.
The distance from the back of the hole to the back wall of the latrine should be at least 15 cm, so that it is not necessary to lean against the wall when squatting.
Make a cover for the latrine hole out of wood, with a long handle (Fig. 2).
CONSTRUCTION
The first step is to precast the squatting slab, as described on the previous page.
Make the hole for the latrine large enough so that it won't become full too quickly. The soil should be firm enough so that the weight of the latrine structure won't cause the hole to collapse. If the soil is firm enough, the foundation slab can be poured around the edge of the hole (first remove the top soil) (Fig. 1). If the soil is a bit soft, reinforce the foundation slab.
If the soil is very soft, it will not be able to bear the weight of the construction. Then it will be necessary to construct a lining for the hole to be sure that it will not collapse. The lining can be made with blocks; or in a round hole with concrete rings, as described under the section on wells. The foundation slab then rests on top of the lining and cannot sink down into the soft soil (Fig. 2).
When you construct the foundation slab, fix some steel rods or holdfasts in the concrete, as shown in Figs. 1 & 2. These can be used later to anchor the wooden structure of the toilet.
When the foundation slab is cured, place the precast squatting slab on top of the foundation and secure it in place with a weak mortar (Fig. 3).
TOILET ROOM
The toilet room can be built from mud or landcrete blocks, and plastered with mud. However, be sure that the foundation can support the walls because they are heavy, and in soft soil they may sink down and collapse the hole. Also, when the hole is full and a new one has to be dug, the walls have to be built completely new.
Because of the above problems with block walls, it is advisable to construct a light-weight structure out of timber and metal sheets. The light-weight structure can be removed when the pit is full and installed again over a new pit. The squatting slab can also be re-used (Fig. 1).
The structure must be anchored well to the foundation slab so that it is not blown away in strong winds.
TOILET PARTITIONS
If a community lairine with several compartments is needed, use the system drawn on page 124 of the Drawing Book.
First do the setting out. Then dig the round pits and make foundation slabs around the pits. Construct arches or lay a reinforced concrete beam across the center of each pit.
There are four squatting slabs over each pit. Lay each one carefully so that one edge rests on the concrete beam and two other sides rest on the foundation slab. Use soxne weak mortar between the slab and the supports, to ensure that the slabs are flat and stable.
The partitions between the toilets should be light-weight structures of timber and metal sheetc or waterproof plywood. The outside walls can bo constructed from landcrete blocks or mud.
Many of the materials from the above structure can be re-used after the holes become 2/3rds full and new pits are dug. The light-weight partitlons, the squatting slabs and the reinforced beams can all be taken out and used in the new construction.
PERMANENT LATRINE
If the latrine is constructed so that the pit can be cleaned out when it becomes two-thirds full, then it is no longer necessary to dig a new pit every few years. in the design explained here, the pit contents are removed through a manhole from the outside of the toilet room.
Make a reinforced concrete beam or an arch across the pit (Figs. 1 & 2) to support the back wall of the toilet, the floor, and the concrete manhole cover.
Cast the foundations around the pit and under the future walls of the toilet (Figs. 1 & 2). On top of the foundations cast the floor slab with the openings for the manhole and toilet. The toilet can be made with the same squatting slab design as the other latrines, or a seat may be constructed above the hole (Fig. 3).
The rising walls are constructed directly on top of the floor slab (Fig. 4). They may be built out of mud, sandcrete or landcrete blocks, since the structure will be permanent. Make sure that the toilet room is will ventilated and the roof is securely anchored to the building. The wall in front of the entrance can be built up to about 180 cm high (Fig. 4).
BUCKET LATRINE
One of the oldest and generally least cleanly systems for waste removal is the bucket latrine. As in the cross section in Fig. 1, the squatting slab is set over a collection chamber with a bucket. The chamber should be closed off with a removable fly screen. The bucket should fit into a niche on the floor, so it is always returned to position directly under the hole in the slab when it is replaced after cleaning.
The area behind the latrine should be paved, and a drain and a soak away should be made to get rid of the water used for cleaning the toilet and collection chamber.
The bucket latrine system is only possible where there is an organized system for regular collection and disposal of the bucket contents. This is usually not possible in rural areas.
AQUA PRIVY SYSTEMS
An aqua privy is basically a septic tank directly under a latrine. Its advantages are that it has fewer problems with smells, flies, and disease spreading than a regular latrine. However, at least two buckets of water must be poured into the privy every day for it to operate properly, and this can be a problem where there is no water source nearby.
An aqua privy for the use of one family may hav pit which is about 1 cubic meter in volume (about 0,15 cubic meters per person) The manhole should be large enough so that the sludge can be removed from the pit from time to time; whenever the tank is one-third full. If the tank is not emptied in time the drain pipe will become blocked and the system will fail.
Add some reinforcement to the squatting slab over the tank to support the back wall of the toilet. Make sure that the inside of the tank is waterproof, because if it leaks the water level cannot be maintained and smells can pass through the chute. If necessary paint the inside walls of the tank with waterproof paint. Make sure that there is a good ventilation system, with a fly screen over the end of the pipe which ventilates the tank (Fig. 2).
It is very important to maintain the water level within the tank. If possible, washing facilities can be made nearby and connected with the tauk, so that tho water from the sink or shower room goes into the tank and maintains the water level.
SOAKAWAYS
A soakaway is basically a hole in the ground filled with stones, through which water can seep away into the surrounding soil instead of forming a pool on the surface of the ground where mosquitos can breed.
Dig a hole and fill it with large stones at the bottom and smaller ones at the top. Drain pipes from bathing areas, etc. can lead into the pit; they should end up in the centre. Cover the soakaway with soil, but make sure that the soil does not enter between the stones and block the drainage pipe. The soakaway can be covered with a layer of concrete to keep the top soil out (Fig. 1).
Soakaways should be at least 30 m away from wells or streams, and never uphill from a water source.
MANHOLES
Sometimes manholes are needed where long pipes have to be inspected at intervals. Manholes give easy access to the pipe junctions. A typical manhole layout is shown in the Drawing Book, page 125. This manhole can also serve as a kind of junction hole, from which mors than one pipe can cross. The slope should be the same for pipes entering and leaving the manhole (Figs, la & lb).
SEPTIC TANKS
Septic tanks are designed in such a way that the water takes at least 24 hours to pass through the system. During that time the heavier solids will settle to the bottom, forming the sludge. in the tank the solids are gradually broken down and become much reduced in volume.
Septic tanks should have two compartments (Fig, 2). The first compartment is twice the size of the second compartment. intermediate walls are sometimes made in order to reduce the speed of the water flow, and to make the distance that the water has to travel longer.
The sludge has to be removed from the tank every few years, whenever it becomes 1/3 full. This sludge will not be Bafe to use as fertilizer until it has been composted for several months. The water flowing out from the tank will also be contaminated with bacteria and disease organisms.
