Applying a circular economy approach to valorize spent coffee grounds

Abstract

The Coffee industry faces a range of sustainability issues including energy demand, waste management and greenhouse gas (GHG) emissions. This study develops and analyses an experimental WTE proposal using an independent Coffee Company's integrated energy-waste management strategy, to achieve a circular economy (CE) system: treatment and reuse of spent coffee grounds (SCG) to fuel the roasting-phase. The SCG's chemical properties and combustion characteristics were determined using international standard methods and evaluated against conventional fuels to establish their energetic-potential; this included elemental composition, thermochemical behaviour, higher heating value (HHV) and carbon dioxide emissions (CO2e). A Life Cycle Analysis approach was utilised to calculate the CO2 emissions for each fuel sample and roasting scenario, demonstrative of the roasting-phase and representative of Scope 1 emissions. The SCG were more energetic than conventional-biomass, however, less than fossil fuels. SCG utilisation achieved carbon savings of 5.06 kg CO2e / kg−1 fuel for each batch roasted compared to a conventional approach, and a further 0.77 kg CO2e / kg−1fuel for each batch roasted resulting from integrated subsystems (total 5.83 kg CO2e / kg−1 fuel). SCG high nitrogen concentration may still cause concerns about GHG emissions. The integrated energy-waste management strategy facilitates industrial symbiosis, clearly achieving waste reduction by exercising CE characteristics, namely ‘resource-sharing’ and ‘increased cooperation’ between coffee roasteries and shops, enabled by zero-waste principles and Coffee Company's reverse-logistic Product Service Model. Recovering value from SCG as part of the coffee supply chain shows significant promise towards achieving a CE system, indicated by reduced raw material extraction, waste generation and CO2 emissions.