and the Efficacy of Pit Latrine Additives - Water Research Commission

pipe and also prevent the exposure of faeces to atmospheric air, escape of odours and flies to the
surrounding environment.
1.1.3 Superstructure
The superstructure provides privacy to the users, protects the pit from rain and sun, provides enough
shadow to the pedestal, thereby preventing flies that are newly formed from leaving the pit itself and also
channels air through the pedestal to the vent pipe thereby controlling faecal odours. The superstructure is
usually constructed on or around the cover slab, and out of similar materials to the main house of the family
to which it is attached.
1.1.4 Vent pipe with fly-screen
The main function of the screened ventilated pipe is to control odour and flies. It is necessary that the
screened ventilation pipe stands completely straight in order to allow penetration of light into the pit. The pipe
should extend 500 mm above the roof of the superstructure; movement of wind across the top of the vent
pipe induces a suction that draws air out of the vent pipe. Flies are attracted to the odours at the top of the
vent pipe, but cannot get into the pipe due to the presence of a fly-screen. Since flies are attracted by light,
flies that are already in the pit will be attracted to the top of the vent pipe from the inside by the sunlight that
shines down the vent pipe, but will not be able to escape due to the presence of the fly-screen. Thus the
screened vent pipe should control odours and flies in the pit. (Mara, 1984).
1.1.5 Pedestal, lid and superstructure door
In Southern Africa, pit latrines are commonly built with a pedestal (squat plates or squat holes are more
common in central and northern Africa and Asia). A variety of pedestal designs and materials are used,
including cement, plastic and porcelain. Cement pedestals are sturdy and fairly inexpensive, but tend to
absorb urine and thus the entire superstructure acquires an unpleasant smell over time when these are
used. The most important feature of the pedestal is that it should have a lid that does not fit tightly to the
seat. The lid prevents the ingress of light into the pit, thus discouraging flies from exiting through the
pedestal. However, the lid should not prevent the ingress of air into the pit since suction induced by the
movement of wind across the top of the vent pipe will pull air into the pit via the pedestal, thus ensuring
odour control.
Similarly, the superstructure should be fitted with a door and roof to keep the latrine dark, further reducing
the ingress of light into the pit via the pedestal.
1.2 Project aims
This project proposed to undertake field and laboratory investigations of VIPs and their contents in and
around the eThekwini Municipal area in order to understand the conditions to be found in the pits and to
propose design and operating practice that will extend the life of pits. The study proposed to concentrate on
three main areas of interest:
Water balance in pits under different hydrogeological conditions (water draining into the pit, water
draining out of the pit, no water transfer in or out of the pit)
Stabilisation rates in pits (organic, pathogens)
Efficacy and action of additives on pit processes
The project contract specified the following aims for this project:
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