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Waste composition analysis

The first week of May was taken up with finishing Gambia’s first ever full-scale waste composition analysis.

Over five days, 10 sorters, including your intrepid consultant, sorted through two-and-ahalf tonnes of municipal waste in 25 samples (pictured). Just imagine the scene: 40°C, full personal protective equipment, a large amount of smelly organic waste and some very inquisitive cows. Yes, dear reader, I feel I have earned my waste management stripes.

So, what did we find? What wasn’t there was just as interesting as what was. Around a third of the waste was organic and, while this is in line with what might be expected in the UK, it is very much at the lower end of what is generally indicated for sub-Saharan Africa. A possible explanation is that such waste is seasonal, and we were at the end of the long dry season so much organic waste was relatively desiccated which reduces mass.

Almost a fifth of the waste by weight comprised plastic, and over half of this was plastic film. This is a massive proportion given the low density of the material.

But what was arguably most interesting was what wasn’t there: negligible amounts of PET, despite the ubiquity of plastic drinking water bottles across the country. This indicates an effective informal reuse system with water bottles being used repeatedly to hold a variety of liquids. Indeed, the bottles provided for drinking throughout the study were all spirited away at the end of each day to be refilled with a local drink, wonjo, brewed from hibiscus flowers and copious amounts of sugar.

There was also little glass, despite its widespread usage for soft drinks, which indicated the efficacy of the bottle deposit schemes in place, and very little metal, demonstrating the impact of informal metals collections. Indeed, children could be found around the site collecting and flattening ferrous metal containers.

A slightly depressing finding was that around 4% of the waste was disposable nappies, a proportion I found surprisingly high, indicating the onward global march of such products, even across the developing world.

All this shows the importance of basic baseline research before considering any sort of action. Had we assumed a similar waste stream to the UK then metals, glass and paper would have been high on the list of recyclable targets. These materials will be left to local reuse and recycling systems that are already clearly working effectively, with our focus being on materials that actually need further attention and require improved management.

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