Tapping the bioenergy potential of milled coffee wastes: a study on the pyrolysis kinetics, response surface methodology, and techno-economic feasibility

The thermal degradation of milled coffee waste was investigated in a fixed‐bed reactor using iso‐conversional kinetic modelling, yielding an average activation energy of 43.94 kJ mol⁻¹. A central composite design optimisation was performed, and the optimal operating conditions were identified as 370 °C, 5 °C min⁻¹, and 48 min to produce 328.42 g biochar and 109.74 g aqueous fraction per batch (750 g) of feedstock. The optimal process consumes 0.49 kWh energy, and the model was repeated with 98.16% accuracy. Techno‐economic analysis demonstrated strong viability with a net present value of INR 41,607.3, internal return rate of 14%, and a payback period of 9.18 months. A cradle‐to‐gate life-cycle assessment compared pyrolysis to gasification, combustion, and composting. Pyrolysis emitted 150 kg CO₂ and 1.62 kg CH₄ (198.6 kg CO₂-eq/t), sequestering 437.33 kg C in biochar (–306.133 kg CO₂-eq) for a net global warming potential (GWP) of −107.53 kg CO₂-eq and a positive energy balance (+1.76 MJ/t). Gasification, combustion, and composting exhibited higher net GWPs (135.6, 160.2, and 16.4 kg CO₂-eq/t, respectively) and inferior energy balances. Optimised pyrolysis thus delivers superior biochar yield, energy recovery, economic return, and greenhouse‐gas mitigation among evaluated waste‐to‐energy routes.