Used Coffee Grounds: an opportunity or just a waste product?
By Pru Mhlophe, James McCune Smith and GALLANT Post graduate researcher working the use of used coffee ground for heavy metal remediation in soils around Glasgow
Worldwide an estimated one billion tonnes of coffee waste are produced each year (Jagdale et al., 2019). Most of this goes into landfills in what is probably the biggest lost opportunity. Used coffee grounds are one of the most versatile compounds available and it’s great to see Grounds for Recycling profiling the many ways they can be repurposed. The beauty of them is that they are functional even in their raw state with very minimal processing required. Processing can be done that converts grounds into biochar by heating them to high temperatures in the absence of oxygen. These processes further increase and improve the ways that grounds go on to have further uses.
Figure 1 below shows the opportunities for coffee grounds in soils; the industrial uses are beyond the scope of this article.
Fig. 1. The opportunities of used coffee ground
At the University of Glasgow, we are getting ready to undertake a research study on how effective used coffee grounds are in the remediation of pollutants in the environment. So far, five coffee machines in the Advanced Research Centre building of the University, have produced 12.5kg (dry weight) of coffee grounds in two weeks, see Figure 2. We will be testing specifically how these used coffee grounds both raw and as biochar have the potential to immobilise heavy metals and other contaminants in soils.
Fig 2: Photos from the coffee ground collection process
As part of the NERC-funded GALLANT research project, which uses the city as a living lab to take a whole system approach to the city’s environmental challenges, this study looks at how used coffee grounds can assist in removing carbon dioxide from the atmosphere, remediating vacant and derelict land. Many of Glasgow City Council’s 884 vacant and derelict sites have some form of contamination, including heavy metals and other organic contaminants.
If we can work out the most effective way for used coffee grounds to uptake contaminants, there is great potential for used coffee grounds to improve the city rather than go to landfill.
Based on known research data and our calculations, a month’s worth of coffee grounds has enough potential to decontaminate 2 to 3m2 of land to a depth of 30cm or a tonne of excavated contaminated soil. For those interested in more details, see here.
Think of all the coffee grounds from Glasgow University, let alone the whole city of Glasgow. There is more than enough to reach the 35,000 tonnes per year required for just a third of the vacant, derelict and possibly contaminated land.
Just think, if five machines can decontaminate 1-1.5 tonnes, then a single coffee machine with an avergae usage of 15-20 people per month can decontaminate 200-300kg of soil. What an opportunity!
