Abstract

The aim of this study is to investigate the performance of a pilot-scale plug-flow reactor (PFR) as a biorefinery system to recover chemicals (i.e., volatile fatty acids (VFAs)), and biogas during the dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The effects of the hydraulic retention time (HRT) on both outputs were studied, reducing the parameter from 22 to 16 days. In addition, VFA variation along the PFR was also evaluated to identify a section for a further valorization of VFA-rich digestate stream. A particular focus was dedicated for characterizing the community responsible for the production of VFAs during hydrolysis and acidogenesis. The VFA concentration reached 4421.8 mg/L in a section located before the end of the PFR when the HRT was set to 16 days. Meanwhile, biogas production achieved 145 NLbiogas/d, increasing 2.7 times when compared to the lowest HRT tested. Defluviitoga sp. was the most abundant bacterial genus, contributing to 72.7% of the overall bacterial population. The genus is responsible for the hydrolysis of complex polysaccharides at the inlet and outlet sections since a bimodal distribution of the genus was found. The central zone of the reactor was distinctly characterized by protein degradation, following the same trend of propionate production.

Highlights

  • Dry thermophilic anaerobic digestion (AD) of OFMSW provides a good alternative to wet technologies in both the production of volatile fatty acids (VFAs), as chemicals building blocks and the production of biogas for energy recovery

  • The concentration of VFA was inversely correlated with hydraulic retention time, reaching the maximum of 4421.8 mg/L when HRT was minimum, namely, 16 days

  • Inside the plug-flow reactor (PFR), the concentration of VFAs was a parabolic curve with the maximum in the central zone but nearer to the outlet

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Summary

Introduction

Received: 16 November 2021Accepted: 5 January 2022Published: 11 January 2022Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/).The most recent European policies address the valorization of biowaste towards the fulfillment of circular economy [1] and bioeconomy [2] principles. Despite that the European waste hierarchy has food waste prevention at the top, food waste still accounts for 60% of the biowaste currently generated in the European Union (EU). In addition, the

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