and the Efficacy of Pit Latrine Additives - Water Research Commission

sludge and therefore could be undertaken with a large number of replicates. Samples were kept in a fume
cupboard under high humidity conditions to minimise mass change by drying. Half of the experimental units
were open to simulate pit conditions with oxygen ingress, while the other half were closed to observe the
effect of the additives in lower layers when the oxygen supply is cut off. Mass loss results were compared to
those from units containing untreated pit latrine contents, and pit latrine contents with water or alkaline
solution. Chemical analyses of the pit latrine material before and after the test were performed and the
results used to ascertain whether any significant changes in sample characteristics could be observed
between different treatments.
In the course of this project a selection of pit latrine additive suppliers were contacted and asked to provide
information relating to the composition and efficacy of their products. Samples of these products were tested
using the protocol described.
4.3 Laboratory-scale testing of pit latrine additive products
Commercial pit latrine additives were found to contain large concentrations of active micro-organisms with
the ability to utilise organic substrates. However, neither the field trials, nor the laboratory trials provided
evidence that the use of these products could result in a significant reduction in either mass or volume of pit
latrine contents. There were two probable causes of this result:
In the study into processes in pit latrines, it was concluded that much of the biodegradable material in
faecal sludge is degraded very shortly after material is added to the pit latrine, mediated by the
presence of naturally occurring micro-organisms present in the pit latrine and the added faeces. Thus
the residual biodegradability of pit latrine contents is low compared to added faeces, and significant
decreases in the volume or mass of the bulk of the buried contents through biological degradation are
not possible;
The high concentration of naturally occurring degradative micro-organisms in the faeces and pit latrine
contents was of a similar order of magnitude to the concentration in the added pit latrine additives.
However the overall number of micro-organisms in the active surface layer of the pit latrine (calculated
by the concentration of micro-organisms multiplied by the mass or volume of the active surface layer)
was far greater then the total number of micro-organisms added with the treatment of commercial pit
latrine additive. Thus, although the added micro-organisms may have been successful in degrading
organic material, the increase in the rate of degradation due to treatment with pit latrine additives was
negligible since high degradation rates were observed in untreated samples.
An important observation was made in understanding the results of these experiments: Although pit latrine
content samples should be well mixed before being used in pit latrine additive trials, a random distribution in
biodegradation and mass loss rates in sub-samples must be expected due to the slightly different nature of
the material in each sub-sample. Thus the conclusion that a treatment has a significant effect on degradation
or mass loss rates observed in control or reference treatments must be made on the basis of a systematic
change observed in a number of replicates of the same treatment.
Thus when a particular unit exhibits a higher rate of mass loss than other units (as is seen in the first
replicate of treatment K, Figure 3), this cannot be interpreted as having been caused by the treatment unless
the other two replicates show an increased rate of mass loss when compared to the control units.
Under aerobic conditions (no limitation of oxygen supply), there was no significant increase in the rate of
degradation of pit latrine contents due to the addition of commercial pit latrine additives at the recommended
dosage rates (g additive/ m 2 pit latrine contents). Similarly under limited oxygen supply conditions (anaerobic
conditions) the rate of degradation was not enhanced by addition of commercial pit latrine additives at the
recommended dosage rates, and in fact, the overall rates of degradation in terms of observed mass loss
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