Published in Biomass and Bioenergy and Clean Technologies, the studies showcase how coffee waste could be used effectively to filter heavy metals, such as lead, copper and zinc, from water.
Coffee is one of the most widely consumed beverages worldwide. In 2021–22, global coffee consumption exceeded 176 million bags (around 60kg per bag), marking a notable rise from approximately 167 million bags in the previous year.
The growing global consumption generates substantial waste, particularly spent coffee grounds (SCGs), a byproduct rich in organic matter.
SCGs are porous, plant-derived materials that have excellent potential as adsorbents that could prevent coffee from going to waste.
Various other adsorption materials have also been tested for filtering water and metal ion removal, including resins, clay, rice husks, banana peels, and tea leaves.
By heating used coffee grounds, taken from Loughborough University’s Edward Herbert Building cafeteria, the research team, in collaboration with Banaras Hindu University (India), produced highly porous biochar, a carbon-rich material, often used to improve soil quality.
After optimising the temperature and duration of the heating, they could remove up to 98% of lead from water, with the biochar holding 4.9 mg of lead per gram.
The study by researchers at Loughborough University demonstrated that the raw coffee waste, also collected from the Edward Herbert Building cafeteria, can be used directly without any further processing to remove heavy metals (eg. copper and zinc) from water at low metal concentrations.
The new research also demonstrates that coffee waste can be used in combination with other materials (eg. rice husk) to achieve heavy metal treatment.
Academics examined how contact time, type of adsorbent, and metal concentration affected heavy metal removal efficiency and found that more than 96% of metals could be removed. They found that the raw coffee waste performed better at low metal concentrations (2.5 ppm copper, 10 ppm zinc), whereas a coffee and rice husk mix performed slightly better at higher metal concentrations (>5 ppm copper, >25 ppm zinc).
Dr Monika Mahajan, lead author on the first study, said: “This work demonstrates how an everyday waste such as spent coffee grounds can be transformed into a high-value, sustainable adsorbent for removing toxic metals from water. By optimising the decomposition conditions, we were able to significantly enhance the material’s performance while keeping the process low-cost and environmentally friendly. It is exciting to see a circular-economy approach translate into a practical solution for real-world water treatment challenges.”
Dr Basmah Bushra, lead author on the second study, added, “Our studies show that what we often dismiss as waste, like spent coffee grounds, can actually become powerful materials in tackling environmental pollution. By turning waste into adsorption material, we can not only reduce landfill burdens but also create affordable materials for cleaning up contaminants. This is a simple but effective illustration of circular-economy thinking in action”.
Dr Diganta B. Das, Reader in Porous Media at Loughborough University, explained the value of the findings. He said: “It is fantastic to see the excellent work that Monika Mahajan and Basmah Bushra have carried out, together with all other colleagues. They have worked incredibly hard to deliver these results and show that coffee waste is not a waste at all — it can be transformed into high-value materials, enhance material circularity in our day-to-day activities and clean the environment.”
By using biochar to filter water, the findings have created a low-cost and eco-friendly way to clean water and reuse coffee waste. This practice supports the circular economy and can be scaled up for real-world water treatment.
These findings further showed that using coffee waste is a cheap and widely available material for cleaning heavy metals from contaminated water.