Spent coffee ground as renewable energy source: Evaluation of the drying processes

Area of Science:

• Biomass energy
• Waste valorization
• Materials science

Background:

• Spent coffee grounds (SCG) represent a significant environmental challenge.
• SCG can be transformed into valuable biomass pellets for energy generation.
• Low moisture content (<10%) is crucial for safe SCG storage and preventing microbial growth.

Purpose of the Study:

• To determine the optimal drying method for SCG.
• To assess the impact of drying on SCG composition.
• To qualify dried SCG as a viable renewable energy source.

Main Methods:

• Comparison of three drying techniques: oven drying, solar drying, and open-air sun drying.
• Evaluation of SCG samples at different tray thicknesses (1.25, 2.5, and 4 cm).
• Analysis of SCG composition and color changes post-drying at approximately 75°C.

Main Results:

• Solar drying achieved 10% moisture content in 10 hours for 2.5 cm thick samples.
• Oven drying reached 7% moisture in 6 hours, while open-air sun drying took 10 hours for 37% moisture.
• Solar drying demonstrated the best balance of energy efficiency and dried SCG quality.
• SCG stored at room conditions reached an equilibrium moisture content of 8%.

Conclusions:

• Solar drying is the most advantageous method for processing SCG into a renewable fuel.
• Drying significantly alters SCG composition, affecting chemical groups and color.
• Dried SCG, with appropriate processing, can serve as a sustainable energy alternative.