and the Efficacy of Pit Latrine Additives - Water Research Commission

3.3.1 Techniques for characterising pit latrine samples
Where appropriate, Standard Methods (APHA, 1998) have been used to analyse the pit latrine samples.
Where no appropriate method was published, adaptations of existing methods or entirely new methods were
developed. Each methods and the principle behind the measurement is presented here.
3.3.1.1 COD
Chemical oxygen demand (COD) measures the amount of oxygen required to completely oxidise a sample
of organic material to CO 2 , H 2 O and NH 3 . It is a measure of the organic material in a sample that is not
dependent on the chemicals that make up the material. It does not provide an indication of the biologically
available organic material in the sample, but is simple and accurate to measure, and therefore is regarded as
a reliable indicator of organic content. It is also a useful indicator of the energy required to stabilise the
sample. COD was measured for whole (unfractionated) samples and for filtrate of filtered samples, or
supernatant of centrifuged samples. The last two measurements were used as an indication of the dissolved
organic material in the sample. COD was measured using the open reflux method for particulate samples
and the closed reflux (titrimetric) method for soluble or filtered samples according to Standard Methods
(APHA, 1998).
3.3.1.2 Biodegradability
The serum bottle technique (Owen et al., 1978) was used to measure the amount of anaerobically
biodegradable COD in a sample. The sample to be analysed was incubated in a 125 ml serum bottle with a
portion of healthy anaerobic sludge, with a non-limiting supply of nutrients and the biogas production
quantified. The biodegradable COD fraction was calculated from the difference in methane production from
bottles containing sample, and control bottles that contained only anaerobic sludge and nutrient solution.
3.3.1.3 Characterisation of solids
Measurement of total solids and organic solids were performed according to Standard Methods (APHA,
1998). The difference between wet and dry solid masses recorded in the total solids analysis was the
moisture content of the sample. Pits situated in locations with well-drained sandy or fractured rock geology
are likely to have low moisture content, while pits built in clay, or in areas with a high water table are likely to
retain considerably more moisture.
3.3.1.4 Anaerobic Activity
Simple gas production measurements from samples that were anaerobically incubated in serum bottles
(without additional biomass or sludge) were obtained. These indicate baseline anaerobic activity in samples
without any intervention.
3.3.1.5 Methanogenic Activity
Measurements of methane production rate were obtained from samples that were anaerobically incubated in
serum bottles (without additional biomass or sludge) were obtained by measuring the total gas production
rate and the methane composition. The methane production rate was calculated by mass balance using the
same method as for biodegradability (section 3.3.1.2)
3.3.2 Results of studies characterising the contents of pit latrines
Faeces do not have well defined characteristics, but will depend on the diet and general state of health of the
person who produced them. This study investigated characteristics of fresh faecal material and samples
obtained from pit latrines. The purpose of the study was to obtain detailed characterisation of both faecal
material and pit latrine samples to develop a sense of what the major differences between the different types
of faecal sludge are, and what might have caused them (i.e. what happens to the material in the pit). In
contrast to other parts of the study, a differentiation was made between particulate and soluble
characteristics. It was acknowledged from the beginning that the faeces used in this study may not have
been similar to those that went into the pits from which samples were drawn.
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