South Korean researchers have developed a process that transforms wet spent coffee grounds directly into high-calorific biochar in under two minutes, bypassing the energy-intensive drying steps that have long constrained biomass valorisation.
The flame plasma pyrolysis (FPP) method, developed at the Korea Institute of Geoscience and Mineral Resources, uses an atmospheric-pressure plasma jet fuelled by liquefied petroleum gas to process coffee grounds at around 55% moisture content — with no pre-drying or de-oiling required.
At the optimal treatment time of 90 seconds, the process achieved a mass reduction of 83.3% and produced a biochar with a higher heating value of 29.0 MJ/kg — comparable to standard anthracite coal and around 33% higher than the raw feedstock. Fixed carbon content increased approximately threefold, from 15.6% to 46.2%, while sulfur was completely eliminated, promising negligible SOx emissions during combustion.
The researchers attribute the rapid pore development to what they describe as a 'popcorn effect': the intense heat flux triggers flash evaporation of the material's inherent moisture, generating internal pressure that expands the carbon matrix and creates a highly porous structure. At 90 seconds, specific surface area peaked at 115.4 m²/g, compared with just 1.5 m²/g in untreated grounds.
The process represents a 90- to 120-fold reduction in residence time compared with conventional pyrolysis methods, which require extended pre-drying and treatment periods. The researchers calculate a specific energy consumption of approximately 154 MJ/kg of biochar at optimal conditions, and suggest the compact system is suited to decentralised, on-site deployment — removing the logistical burden of transporting high-moisture waste.
Over 10 million tonnes of spent coffee grounds are generated globally each year, the majority of which are landfilled or incinerated.
Flame plasma converts wet coffee waste into high-grade biochar in 90 seconds
