Scientists find clever new way to upcycle used coffee grounds

Coffee grounds as a replacement for sand

As global cities grow and expand, the demand for construction materials like sand – an essential component in concrete – is rapidly growing, placing stress on our natural environment.

Extracting a finite material such as sand from river beds and banks destabilises the ecosystem by increasing erosion, altering river flow, and destroying habitats. In places where sand mining occurs at high levels, it can have negative consequences for groundwater levels, water quality, and food supply for surrounding communities.

This is where used coffee grounds can come in as a sustainable solution, however, they cannot be added directly to concrete because they will leak chemicals that weaken the building material’s strength.

The team of researchers at RMIT University heated coffee waste to over 350 °C, while depriving it of oxygen in a process called pyrolyzing. Pyrolyzing breaks down the organic molecules in a material, leaving behind porous, carbon-rich charcoal called biochar that can be mixed with cement.

Having successfully created the coffee-cement mixture, the scientists are now assessing how the hybrid coffee-cement performs under freezing and thawing cycles, water absorption, abrasions, and other environmental stressors.

The researchers say that they are also experimenting with other organic material such as wood, food, and agricultural waste to see if it can be used as biochar, and testing it for durability under different applications.

Upcycle at home

While scientists get to work on finding a sustainable and scalable way to turn used coffee grounds into ready-made concrete reinforcement, there are plenty of ways to ensure the coffee grounds piling up in your kitchen aren’t wasted.

If you’ve got a green thumb, you might already know that coffee grounds make a great fertiliser for plants that thrive in slightly acidic soil. Azaleas, hydrangeas, and rhododendrons, love to be planted in soil sprinkled with used coffee grounds because this makes the soil rich in nitrogen and other minerals.

These same minerals also make coffee grounds a great addition to compost piles. Nitrogen helps to break down organic matter like food waste at a faster rate, speeding up the natural composting process.

When mixed with soil, coffee grounds are also believed to repel pests and insects like slugs, snails, and other bugs, while suppressing weeds by helping soil around plants retain moisture.

Carrying out composting at home might not seem that impactful, but until science figures out how to implement large-scale circularity solutions like turning coffee grounds into concrete reinforcement, any small act still makes a positive difference in the long run.

So go on, make another brew! Just be sure to throw those used coffee grounds in the back garden when you’re all done.