Inoculum-to-substrate ratio and solid content effects over in natura spent coffee grounds anaerobic digestion

Author(s)

Dias, M. E. S. ; Takeda, P. Y. ; Fuess, L. T. ; Tommaso, G.

• Document type: Journal article
• Source: Journal of Environmental Management; v. 325, p. 12-pg., 2023-01-01.

Abstract

Coffee is the second most traded commodity worldwide, and its production is associated with the generation of a large number of residues, which are underused and disposed of in landfills. Notably, the coffee industry annually generates approximately 6 million tons of industrial spent coffee ground (ISCG) when extracting coffee flavorings to produce soluble coffee. That resource loss scenario has been highlighted in sustainable waste management contexts as an opportunity to improve the coffee circular economy. Despite ISCG bioconversion to methane potentially meets the waste-to-energy purposes of reducing residues disposal in landfills, decreasing greenhouse gas (GHG) emissions, and increasing renewable energy sources, data about anaerobic digestion (AD) of ISCG remains quite restricted. That limitation becomes more apparent owing to the lack of data focusing on AD key parameters for ISCG as substrate. This study assessed the influence of inoculum-to-substrate ratio (ISR) and the solid content influences on mesophilic (37 degrees C) ISCG-AD throughout the Response Surface Methodology (RSM) and Central Composite Design (CCD). Results revealed that both factors, ISR and solid content, should be kept above a certain threshold of 0.5 and 6.0 gTVS L-1 to ensure experimental reliability, as well as reproductively and above 1.0 and 8.0 gTVS L-1 to avoid underestimation on the MY potential achieved. Concerning ISCG-AD kinetics, the quadratic model optimum condition was at 1.36 and 14.83 gTVS L-1 for ISR and solid content, respectively. This optimum range for ISR and solid content could guide further development of process con-figurations for mono-and co-digestion of ISCG, avoiding underestimation of the MY potential and extended incubation periods. (AU)

• FAPESP's process: 21/15022-6 - Association of pre-treatments and anaerobic digestion aiming energy valorization of the main residues in the coffee production chain
• Grantee: Giovana Tommaso
• Support Opportunities: Regular Research Grants
• FAPESP's process: 15/06246-7 - Biorefinery concept applied to biological wastewater treatment plants: environmental pollution control coupled with material and energy recovery
• Grantee: Marcelo Zaiat
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 20/07737-2 - Hydrothermal and chemical pre-treatments of wastes from the soluble coffee production coupled to metanogenesis
• Grantee: Maria Eduarda Simoes Dias
• Support Opportunities: Scholarships in Brazil - Doctorate