and the Efficacy of Pit Latrine Additives - Water Research Commission

The presence of large amounts of non-degradable material in a pit has two effects: (i) the pit fills
quicker due to the large material addition rate and (ii) the rate at which biodegradable material is
covered over in the top layer and therefore deprived of oxygen is increased resulting in lower potential
for aerobic degradation during residence in the top layer
The amount of moisture present in the pit contents will have an effect on both biological and transport
processes. Moisture assists in solubilisation of potentially soluble components (including salts, easily
digestible organic material and carbon dioxide). It allows movement of soluble components relative to
stationary solid components (Martin et al., 2003). It also affects the concentration of dissolved
components: addition of water to the pit decreases the concentration of salts and organics leached out
of solid material. These concentrations may have a significant effect on the rate of biological activity in
the pit, or the extent of microbial inhibition if the latter is caused by a water soluble component.
The presence of organic material in the pit from e.g. disposal of kitchen refuse or addition of soil will
contribute to the load and diversity of micro-organisms in the pit and assist in the establishment of a
healthy natural micro-organism population in the pit provided that pit conditions are conducive to such.
In summary, it is not possible to predict what will be in any particular pit without at least looking into the pit, or
digging the contents out. Considerable variability may be expected in organics content, moisture content,
non-biodegradable content and micro-organism population.
3.2.3 What happens to things in the pit
What is added to a pit depends mostly on user habits and to a lesser extent on the physical design of the
structure. What occurs in the pit depends to on the same two factors; in addition, the geo-hydrology of the
locality of the pit will also affect the processes that occur therein.
An important step in developing a strategy for improving the design and operation of pit latrines is to
understand what processes occur in the pit, how they occur, and what factors will affect the rate at which
they occur. Once the processes are understood, it becomes possible to propose methods of enhancing the
processes either through the addition of chemical or biological agents or through simple design changes.
Examination of available literature has indicated that certain factors may have a significant effect on the
performance of a pit latrine). These are summarised in Table 3.1.
Table 3.1: Factors that may affect performance of a pit latrine
Construction and location Operation Maintenance
Construction of walls and base of the Age of the pit
Frequency/history of emptying
pit
Permeability of the walls and base of
the pit
addition of other material (e.g.
household waste)
Amount of seed material left after
emptying
Construction of slab, collar and Ingress of (non-urine) liquid via the Additives used to enhance digestion
superstructure of the latrine
top of the pit
Height of water table (low/high) Rate of filling / number of users Ownership: Communal or private
Type of soil
anal cleansing material
Presence of bedrock or sandy aquifer
Proximity of other pits
From the literature review, the following possible effects may occur in the pit:
Accumulation: Material that does not degrade or drain out of the pit will accumulate and cause the
volume of pit contents to increase.
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