and the Efficacy of Pit Latrine Additives - Water Research Commission

A practical definition was used to differentiate between faecal sludge and household refuse components of
the VIP contents; those that could be macerated using a 1.7 l kitchen blender without damaging the blender
were considered to be faecal sludge. All other material was removed and considered to be household refuse.
No measurements of the relative masses of these two components were made. However, they were
observed to vary widely between pits.
There is clearly considerable variability in pit contents characteristics as shown by the very large difference
between minimum and maximum observed values for all determinants. However, it was observed that the
average values reported here were typical of a large fraction of the pits investigated, and may be considered
reasonable values to use for estimating solids and COD loads in pit latrine material.
There is a clear difference between COD load per mass of dry solid for faeces and pit latrine sludge as
measured in this study. If it is assumed that the majority of COD added to the pit originates from faeces, the
implication is that a considerable amount of organic material is degraded or volatilises in the pit, before it
could appear in the samples that were subsequently analysed for COD. Since the variation in COD load per
mass of dry pit latrine sludge is relatively small compared to the difference between faeces and pit latrine
sludge, the implication is that much of the COD loss occurs soon after the material is added to the pit. This
result is one of the key factors that supports the general theory presented in section 3.1; i.e. that a significant
portion of biodegradable material in faeces disappears through aerobic degradation processes before it has
formed a layer with sufficient volume to be sampled.
3.4 Investigation into the processes in pit latrines
This section summarises the work performed by Magagna and reported in his MSc Eng Thesis submitted for
examination at Politecnico di Milano, Milan, Italy in July 2006 (Magagna, 2006). The work was extended by
Nwaneri and will be included in her MSc dissertation.
The research investigated the degradation processes occurring in VIP latrines. The aims of this work were to
assess:
Physico-chemical characteristics of pit contents at different points in the pit;
Biodegradability of pit contents at different points in the pit;
Methanogenic activity at different points in the pit;
3.4.1 Hypotheses
The research was structured to answer the following questions about the processes in VIPs:
Is the mechanism predominantly an anaerobic degradation process No research has been previously
carried out in order to determine if the conditions are suitable for anaerobic digestion to take place.
What is the role of the water There should be little water added to the pit by the user; the water should
be limited to that contained in the faeces and urine or used for cleaning the toilet, although other water
may arrive in the pit from other sources.
What happens to the biologically inert material/compounds that are added to the pit
It was hypothesised that:
Biologically inert material that is added to the pit does not degrade and is not transported within the pit
or out of the pit (i.e. it remains in association with the solid material with which it was added);
Water plays a role in the diffusion of organic content.
The amount of COD (organic content) decreases with the age of the VIP content; therefore lower
concentrations of COD are expected at the bottom of the pit.
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