From waste to rainforest

By Michael Gregson | Published: 2:00 AM Apr 9 2021
Columns From waste  to rainforest

By Michael Gregson

Sri Lanka produces thousands of tons of coffee waste every year – but a technique being pioneered in another tropical country is using this potentially toxic effluent to regenerate forests.

According to the United Nations Food and Agriculture Organisation, the island produces almost 8,000 tons of coffee beans a year. However, 40 per cent – around 3,000 tons – is discarded pulp from around the seeds that are dried and roasted into the coffee we drink. Chemicals in the pulp can leak into water supplies and cause a range of illnesses from skin and eye irritation to nausea and breathing problems.

Often the coffee pulp goes without treatment directly to waste disposal sites. When this waste is dumped, it pollutes the environment in the coffee producing regions by leaching compounds into rivers, lakes and soil.

The relatively high content of organic acids, caffeine and tannins in the coffee pulp and wastewater can pose a serious environmental threat. The pollution generated from one ton of green coffee is estimated to be equivalent of the pollution produced by 2,000 households.

But the pulp can be beneficial to the environment. A study published by the British Ecological Society shows that spreading it onto deforested, degraded farmland can turbocharge forest regrowth dramatically. 

In 2018, researchers spread 30 dump truck loads of coffee pulp onto about one third of an acre of degraded farmland in Costa Rica, in an area that was tropical forest until the 1950s. They also marked out a similar sized area of the nearby land which did not receive the coffee pulp treatment.  

Two years later, they returned to find tropical canopy covering 80 per cent of the coffee-treated land. “The results were dramatic,” said Dr. Rebecca Cole, lead author of the study. “The area treated with a thick layer of coffee pulp turned into a small forest in only two years, while the control plot remained dominated by non-native pasture grasses.” 

Non-native grasses

The scientists believe that the layer of pulp helped prevent non-native grasses from taking root in the soil, giving native trees the chance to take hold and flourish. The coffee-treated land was also much richer in soil nutrients such as carbon, nitrogen and phosphorus, the team found.  

“It looks like a mess for the first two or three years, and then there’s this explosion of new plants coming in,” said fellow researcher Rakan Zahawi. “It’s so nutrient-rich they’re sort of growing on steroids.”

The key, they found, was to pile on the pulp, using a thick enough layer of pulp in an area flat enough for it not to wash away, and in a climate with a dry period that allowed the coffee to really bake. Essentially, it became like a very successful compost heap.

Although further research is needed, Dr. Cole said the discovery could offer a “win-win scenario,” giving coffee producers an extra revenue source and “jump start” the growth of forest recovery on land cleared for farming. 

“We hope our study is a jumping off point for other researchers and industries to take a look at how they might make their production more efficient by creating links to the global restoration movement,” she said.  

As a widely available waste product that’s high in nutrients, coffee pulp can be a cost-effective forest restoration strategy, which will be important to achieve ambitious global objectives to restore large areas of forest, such as those agreed in the 2015 Paris Accords.

The most common way to restore forests is to plant trees. But it is labour intensive and expensive compared to just dumping a coffee by-product and letting nature do the rest.


While the experiment with coffee pulp successfully jump started forest growth, there are some downsides. “Coffee pulp is really stinky,” says Dr. Cole, who was raised on a Costa Rican coffee farm. “I grew up with the smell but a lot of people find it pretty offensive.” 

It also attracts a lot of flies and other insects. There’s also some concern that it will have negative effects on watersheds, and while this experiment was conducted away from water sources, future research will look at the potential impact on surrounding areas.

However, the scientist remains very positive: “I was kind of sceptical it was going to work. I thought we would just have a greener patch of grass,” Dr. Cole says.

Instead, they got the beginnings of a new rainforest.

By Michael Gregson | Published: 2:00 AM Apr 9 2021

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