Cool new way to convert coffee waste to clean biofuel – cheaply

SUBSCRIBE to our fortnightly e-newsletter to receive more stories like this.  Barista makes an espresso: most spent coffee grounds currently go to landfill, wasting potentially valuable oils and nutrients that have a multitude of other useful purposes.

The café set is set to become a major source of clean, green biofuel with the potential to cut our reliance on diesel from fossil fuels dramatically.

Spent coffee grounds, thanks to their high nutritional and energy value, have huge potential as a greener, cheaper alternative to the land- and water-hogging grain and oilseed crops currently purpose-grown for feedstock.

Right now, however, millions of tonnes of ‘used’ coffee grounds end up in landfills every year.

A few small-scale operators are already converting spent coffee grounds into biofuel, but the multi-step process they’re using is time-consuming and pricey.

The conventional method entails mixing used coffee grounds with extraction solvent hexane and heating the resulting mixture at 60°C for between one and two hours before evaporating the hexane, adding another solvent, methanol, and a catalyst to the oils that remain to create biodiesel and a glycerol (trihydroxy sugar alcohol) by-product, and separating these.

Now, researchers in the Engineering Department at Britain’s Lancaster University have found a way to make the conversion process far more efficient, boosting the commercial viability of coffee biofuel significantly.

Barista at work: there are many potential applications for oil- and nutrient-rich 'used' coffee grounds, including as biofuels, compost and mushroom-growing medium.
Barista at work: there are many potential applications for oil- and nutrient-rich 'used' coffee grounds, including as biofuels, compost and mushroom-growing medium.
Coffeegeek, Flickr CC

Chemical engineers have managed to consolidate the existing multi-stage process into one step, known as ‘in-situ transesterification’, that combines extracting the oils from used coffee grounds and converting them into coffee biodiesel.

The Lancaster University research team, helmed by Engineering lecturer Dr Vesna Najdanovic-Visak, realised that they could combine the processes without hexane, just methanol and a catalyst, saving time and chemical waste.

Moreover, they found that the optimal time to achieve the same oil yield from spent grounds using this simplified process was 10 minutes – a six- to 12-fold reduction in the time needed for full conversion, with a corresponding drop in associated energy costs.

“A huge amount of spent coffee grounds, which are currently just being dumped in landfill, could now be used to bring significant environmental benefits over diesel from fossil fuel sources," she said.

The new process, say the researchers, could, potentially, enable companies to make 720,000-odd tonnes of biodiesel per annum from the nine million-odd tonnes of used coffee grounds that would otherwise be wasted across the UK.

The Lancaster researchers’ findings were published in the Journal of Environmental Chemical Engineering in April 2017.

A cafe latte - now there's a way to turn all that coffee 'waste' into clean, green, cost-effective biofuel, say researchers.
Cheap fuel with your cafe latte? Now there's a way to turn all that coffee 'waste' into clean, green, cost-effective biofuel, say researchers.
Jen Collins, Flickr CC

How much coffee waste are we producing?

Planet Ark’s Coffee Ground Recovery Program Feasibility Study, helmed by Dr Amanda Cameron and Dr Sean O’Malley and released in January 2016, found that:

• Australians consume 6 billion cups of coffee every year. The grounds used to make all this coffee are used once, then discarded immediately.
• There were 921 cafés and coffee shops within the City of Sydney at the time of Planet Ark’s survey.
• The survey found that an average Sydney city café uses 32kg of coffee beans in a week, producing 60kg of spent coffee grounds.
• Nearly 3,000 tonnes of spent coffee grounds are produced each year.
• 93% of cafés send their spent coffee grounds to landfill.
• An average Sydney café spends $900 a year sending its spent coffee grounds to landfill.
• 7% of cafes have their spent coffee grounds collected by an organic waste processor or by customers for composting.
• Spent coffee grounds are collected in cafés separately to other waste streams, with low levels of contamination.

Coffee beans.
Coffee beans are packed with nutrients and oils, most of which are still present once the beans have been 'used' to make coffee.
THINK Global School, Flickr CC

Why is dumping coffee waste such a waste?

According to Planet Ark, spent coffee waste, while rich in potential uses, is “potent waste with negative impacts”.  

• When spent coffee grounds are sent to landfill, they can produce methane and carbon dioxide, greenhouse gases that contribute to global warming.
• The waste coffee grounds also contribute towards the huge finanical cost on tax payers of running and maintaining landfills in Australia.
• While many coffee brands promote the ethical treatment of their growers and the sustainability of their farms, little attention is paid to the environmental impact of the organic waste at the end of the coffee chain in Australia.

Source: Planet Ark 

More information

Read the original paper: Vesna Najdanovic-Visak et al, ‘Kinetics of extraction and in situ transesterification of oils from spent coffee grounds’, in Journal of Environmental Chemical Engineering (2017). 

Read more about recent research into uses for spent coffee grounds.

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