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

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 (...

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Bibliographic Details
Published in:	Journal of environmental management Vol. 325; p. 116486
Main Authors:	Dias, M.E.S., Takeda, P.Y., Fuess, L.T., Tommaso, G.
Format:	Journal Article
Language:	English
Published:	Elsevier Ltd 01-01-2023
Subjects:	Biomethanation Central composite design Coffee residues Inhibition Surface response methodology Industrial spent coffee ground Inoculum-to-substrate ratio Central composite design Domestic spent coffee ground Methane yield Industrial and domestic spent coffee ground Anaerobic digestion Inhibition Index Biomethanation Chemical oxygen demand Coffee residues Surface response methodology Total volatile solids Inhibition
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Summary:	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 °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 configurations for mono- and co-digestion of ISCG, avoiding underestimation of the MY potential and extended incubation periods. [Display omitted] •1. This study investigated ISCG anaerobic digestion (AD) key parameters.•2. ISCG AD assay reproductively and accuracy was dependent of ISR and solid content.•3. Controlling ISR and solid content avoided underrated MY.•4. ISR and solid content showed to have significant effect on ISCG AD inhibition index.•5. The quadratic model enabled to estimate of optimum values for ISR and solid content.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0301-4797 1095-8630
DOI:	10.1016/j.jenvman.2022.116486