and the Efficacy of Pit Latrine Additives - Water Research Commission

The standard deviations in this batch are high, thereby limiting the conclusions that can be drawn from the
results.
Figure AB.4 presents all cumulative gas production data from batches 1, 2 and 3 from Set 1.
2.3 Overall analysis of Set 1 experiments
In this section, the results of batches 1, 2 and 3 are combined and analysed to see if there is are any general
trends that may be observed.
2.3.1 General observations
Experiment 16 was performed twice, in batch 1 and batch 2. The gas production results for experiment 16
from both batches are presented in Figure AB.5. Theoretically these should have been true replicates with
statistically similar results. However, it can be seen that the results from the same experiment performed in
the two batches are significantly different. This result implies either that experimental error within the
experiments is greater than any differences that may be caused by the addition of moisture or alkalinity, or
that there is a correlation between batch number and gas production.
Cumulative gas production after 40 d for the bottle 16 in function of the set
3.50
3.00
Volume of gas produced (Nml/gCOD)
2.50
2.00
1.50
1.00
0.50
0.00
SET 1 SET 2
n° Set
10 j 20 j 30 j 40 j
Figure AB.5: Gas production from experiment T 16 from batch 1 and 2
It must be noted that although a single source of material was used for all experiments in this set, the total
mass of material required was around 2 kg of pit latrine contents, and clearly there will always be substantial
heterogeneity in such a large sample of predominantly faecal material. This may be the cause of the
significantly different behaviour observed in each of the tests.
Examination of Figure AB.4 indicates an apparent negative correlation between moisture content and gas
production, while there might be some positive relationship between additional alkalinity and gas production.
However as seen in Figure AB.1 to Figure AB.3 most measurements of gas production exhibit high standard
deviation. Furthermore, the amount of gas produced per experiment, generally less than 3 ml per bottle over
40 days is substantially less than the maximum possible gas production (420 ml/bottle, see beginning of
Section 2.2). Thus it was concluded that the poor gas production observed may have been due to the fact
that the sample used was fairly well degraded before the beginning of the experiments and hence that there
was only a limited amount of degradation that could occur in the experiments. This implies that the
experiment was fundamentally flawed and that the hypotheses to be tested (viz. additional alkalinity and
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