A circular approach to organic waste on a Caribbean island

Over the past two years, researchers from Wageningen University & Research have investigated various aspects of organic waste flows on Bonaire. Project leader Ana Lopez Contreras discusses the (provisional) outcomes of the project: “Our research was very broad, but an important part was an inventory of waste flows on the island. We looked at organic flows, such as organic waste, manure, sludge, and sargassum.”

Organic waste is already partly reused

This inventory provides insight into how waste can be processed in a more circular manner. Surprisingly, many organic waste streams are already being reused quite a bit. “It was striking that a lot of organic waste, such as old vegetables and fruit, is already being used, especially as feed for animals. Farmers collect this waste and give it to their livestock. As a result, relatively little organic waste is collected and dumped at the island's landfill. In fact, only garden waste and manure are available in large quantities.”

The researchers have found a possible circular application for both of these residues: “Colleague Hellen Elissen, together with her team and students, , tested whether chicken manure can be used as a raw material for the cultivation of insect larvae and the production of frass (insect manure). That appears to work well,” López Contreras explains. The researchers also see opportunities for garden waste: “You can easily process it into compost, possibly together with chicken manure. Compost is already being produced on a pilot scale on Bonaire.”

When, where, and how much sargassum washes up?

Since 2011, large amounts of sargassum seaweed have been washing up on shores in the Caribbean, causing significant damage to nature, the tourism sector, and public health. López Contreras notes, “This has also been an annual problem on Bonaire since 2017, but due to the lack of data on when, where, and how much sargassum washes up, it was difficult to determine how this organic waste can best be used in a circular manner.” The researchers found a solution: “My colleague Matthijs van der Geest and colleagues used satellite images to reconstruct the timing, distribution, and extent of the sargassum influx in the coastal zone of Bonaire. Based on this data, they then determined the biomass of sargassum that can be harvested annually for circular use.”

Using satellite images, they also found a clear positive relationship between the level of sargassum influx and the mortality of mangrove forests in the bays of Bonaire. This information helps identify areas where the mangrove forest needs better protection against sargassum influx. The next step is to see whether the sargassum biomass can be valorized together with other organic waste, for example, by turning it into biogas.

Dealing with organic waste flows on an island

This research on Bonaire highlights the challenges of dealing with organic waste flows on an island.

“We have now done this research on Bonaire, but there are, of course, other islands in the Caribbean with similar challenges surrounding the processing of organic waste,” says Lopez Contreras. “I hope we can work much more with the residents of the islands so that we can share more knowledge. So that people can really implement improvements for the circular use of manure, garden waste, and sargassum.” Some improvements also require adjustments to legislation and regulations. “So you have to tackle this together with the local partners. This way, good ideas don't end up in a drawer but really improve life for people and the health of nature.”