Mathematical Modelling

We’re using our initial research findings to develop mathematical models that simulate latrine pit-filling under different conditions. These will help us understand much faster how to control fill-rates.It can take years for one pit latrine to fill up, and while this can be welcome for users, it makes life difficult for us.

We can’t measure it until it’s happened, so we have to wait to collect the data. To help speed things up, our partners at Imperial College are building a mathematical model of the fill rate so that we can predict it using a computer. The model will represent the main processes that occur in the pit (like aerobic degradation, anaerobic degradation and water drainage) as well as accounting for the condition of the pit and the user behaviour.

The advantage is that on the computer we can speed time up, so we can simulate how quickly a pit might fill in different conditions. For example, we could simulate the fill rate if the user had a growing family or if the summer was particularly dry. By considering several different scenarios we can start to spot whether there are particular factors that affect the fill rate more significantly. We can then focus on understanding these factors even more.

Of course, we need to make sure that model reflects the reality, and this is definitely a challenge. Initially we need to develop an understanding of the complex processes that are occurring, and data is needed to test the model. Alongside pit monitoring in the field, our laboratory experiments also help us to isolate specific processes so we can model them better.

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