Direct Conversion of Food Waste Extract into Caproate: Metagenomics Assessment of Chain Elongation Process.

Simona Crognale,Agata Gallipoli,Daniele Montecchio,Simona Rossetti,Andrea Gianico,Camilla M Braguglia

doi:10.3390/microorganisms9020327

Simona Crognale, Agata Gallipoli + Show 4 more

Open Access

https://doi.org/10.3390/microorganisms9020327

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Abstract

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L−1d−1 with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L−1) was observed at OLR of 15 gCOD L−1d−1 with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process.

Highlights

Recent applications of anaerobic digestion technology are moving towards the generation of high added-value products that includes carboxylic acids such as succinic, lactic, and volatile fatty acids (VFAs) [1]
This study aims at investigating the long-term performances and viability of the fermentation/fatty acids chain elongation (CE) processes in a semi-continuous reactor fed with the liquid extract of real food waste (FW)
The liquid extracts obtained from the solid-liquid separation unit have been characterised (Table 1) in terms of COD, solids, and soluble organic matter and appropriately diluted in order to achieve the desired organic loading rate (OLR)

Summary

Introduction

Recent applications of anaerobic digestion technology are moving towards the generation of high added-value products that includes carboxylic acids such as succinic, lactic, and volatile fatty acids (VFAs) [1]. Particular interest has grown in the biological production of medium chain fatty acids (MCFAs) from renewable resources as a key step to tackle societal dependence on fossil fuels [3,4,5]. These chemicals can be used as precursors of liquid biofuels or commercial chemicals [6]. Caproic acid is obtained from coconut or palm [11] and has a high economic market value [12,13] It derives from chain elongation (CE) reactions in which short chain fatty acids (SCFAs) are converted to MCFAs by using mainly ethanol or lactate as an electron donor [14].

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