Our research is designed to make new discoveries that reduce fill rates of pit latrines and that will feed future innovation.
With partners from leading universities and research institutions around the world, we’re carrying out two closely-linked lines of work:
- Analysing and modelling latrine contents and processes to identify the major factors which control fill rate
- Understanding the influence of pit design, environment, usage and location on decomposition rates and pit lifetime.
Analysing Pit Contents
The major factors which control latrine fill-rate could include environmental conditions (eg pH, surrounding soil type), microbial composition, physical dimensions and degradation pathways.
Our work to understand these factors began with an extensive literature review, from which we developed the following research hypothesis:
Pit latrines are inefficient in digesting organic matter because neither aerobic nor anaerobic processes can work effectively for long enough, due to inappropriate and uncontrolled environments. Both processes stall, resulting in slow or incomplete breakdown of pit contents.
In order to identify major targets for decomposition we started a cross-sectional study in which over 40 latrines were selected on a one-off basis in Tanzania and Vietnam. Samples were collected from these at every 20-30cm of depth and tested for a full range of parameters, both biochemical (protein, carbohydrates, ammonia, ash content, chemical oxygen demand (COD), etc.) and physical (temperature, moisture content, pH). The results are currently being analysed.
Building the Bigger Picture
We also aim to study the full microbial diversity present in each latrine (in collaboration with the Wellcome Sanger Institute and Hurst Bioinformatics). Some latrine samples were selected to be exposed to biodegradability assays. These assays are carried out in collaboration with LeAF (Wageningen University).
Alongside the study of these parameters, we’re collecting of a range of other relevant data related to users (number, habits and diet), latrine structure and latrine dimensions. Some of this data is being collected through household questionnaires, and we are collaborating with a geophysics group based at Bradford University who are exploring the potential of the latest archaeological techniques to identify sub-surface changes in latrines.
Through collaboration with Imperial College, we’re also developing a mathematical model of pit latrine filling. We’ll link this closely with our experimental work to validate and identify factors with the greatest influence on fill rate.
Design, Environment and Usage
Questions about pit design, location, usage and environment are being answered through a longitudinal study of different latrine types in Tanzania and Vietnam. These cover a wide range of locations, design, management and use. This allows us to maximise the contrast and increase the possibility of identifying key factors which affect decomposition and fill rates.
A simple and reliable method for measuring fill rates had to be developed. Using a laser reader, we measure the empty void above the contents of the pit, and repeat this on a two monthly basis so we can see how much it has filled up over time. We carefully calibrated these readings to make sure that we measured the space in the pit accurately and that we always measured from exactly the same spot.
We followed fill rate for at least six months in each latrine, 12 where possible. Every latrine was then sampled every 20 cm from top to bottom, with samples collected from the centre of the pit. These are being analysed for the same parameters and characteristics as in our cross-sectional survey.
We also set-up a volume reduction test in our laboratory in Ifakara, to see if there is a correlation between factors such as COD reductions (or any other parameter) and a reduction in volume.
We’d love to hear from researchers, scientists or product developers who have ideas for how we can solve the exciting challenges we face.
Please get in touch if you think you can help.