Abstract

Purpose: This study aims to investigate the potential of recycling spent coffee grounds (SCG) as an auxiliary biofuel to improve energy efficiency and odor reduction in low-temperature sludge drying systems. Research Design & Data Collection: A pilot-scale closed-loop belt dryer equipped with an inverter-driven scroll compressor (30–200 Hz) was tested under varying compressor frequencies (130, 160, 180 Hz). Experimental data were collected for power use, temperature, pressure, and moisture content. Pilot-scale validation was supported by certified industrial testing (KTI and Daejeon Analytical Research Institute, 2025), confirming a mean SEC of 0.579 kWh kg⁻¹-H₂O and a final moisture of 7.4 wt %, both within design targets. Research Results: The system achieved an average Specific Energy Consumption (SEC) of 0.607 kWh/kg-H₂O and reduced final moisture content to 4.6 wt%, outperforming target thresholds of 0.64 kWh/kg-H₂O and 10 wt%. Operators also reported a noticeable reduction in odor emissions, suggesting SCG's adsorption capacity, though quantitative odor profiling remains a subject of future study. Conclusion: The findings confirm that SCG can serve as an effective auxiliary fuel, enhancing both energy efficiency and environmental performance. The developed system presents a scalable solution for sustainable sludge management within the framework of circular economy principles