Sequential production of lignin, fatty acid methyl esters and biogas from spent coffee grounds via an integrated physicochemical and biological process

Minjeong Lee, Minseok Yang, Sangki Choi, Jingyeong Shin, Chanhyuk Park, Si Kyung Cho, Young Mo Kim

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23 Scopus citations

Abstract

Spent coffee grounds (SCG) are one of the lignocellulosic biomasses that have gained much attention due to their high potential both in valorization and biomethane production. Previous studies have reported single processes that extract either fatty acids/lignin or biogas. In this study, an integrated physicochemical and biological process was investigated, which sequentially recovers lignin, fatty acid methyl esters (FAME) and biogas from the residue of SCG. The determination of optimal conditions for sequential separation was based on central composite design (CCD) and response surface methodology (RSM). Independent variables adopted in this study were reaction temperature (86.1-203.9 C), concentration of sulfuric acid (0.0-6.4%v/v) and methanol to SCG ratio (1.3-4.7 mL/g). Under determined optimal conditions of 161.0 C, 3.6% and 4.7 mL/g, lignin and FAME yields were estimated to be 55.5% and 62.4%, respectively. FAME extracted from SCG consisted of 41.7% C16 and 48.16% C18, which makes the extractives appropriate materials to convert into biodiesel. Results from Fourier transform infrared spectroscopy (FT-IR) further support that lignin and FAME extracted from SCG have structures similar to previously reported extractives from other lignocellulosic biomasses. The solid residue remaining after lignin and FAME extraction was anaerobically digested under mesophilic conditions, resulting in a methane yield of 36.0 mL-CH4/g-VSadded. This study is the first to introduce an integrated resource recovery platform capable of valorization of a municipal solid waste stream.

Original languageEnglish
Article number2360
JournalEnergies
Volume12
Issue number12
DOIs
StatePublished - 2019

Bibliographical note

Funding Information:
Funding: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1D1A1B03029456). Also, this work was supported by “International Environment Research Institute (IERI)” grant funded by the GIST in 2019.

Publisher Copyright:
© 2019 by the authors.

Keywords

  • Anaerobic digestion
  • Fatty acid methyl esters
  • Lignin
  • Organosolv
  • Response surface methodology
  • Spent coffee grounds

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