Dynamic Effect of Operational Regulation on the Mesophilic BioMethanation of Grape Marc.

Josue Kassongo,Andrew S Ball,Esmaeil Shahsavari

doi:10.3390/molecules26216692

Abstract

Wine production annually generates an estimated 11 million metric tonnes of grape marc (GM) worldwide. The diversion of this organic waste away from landfill and towards its use in the generation of renewable energy has been investigated. This study aimed to evaluate the effectiveness of operational parameters relating to the treatment regime and inoculum source in the extraction of methane from GM under unmixed anaerobic conditions at 35 °C. The study entailed the recirculation of a previously acclimated sludge (120 days) as downstream inoculum, an increased loading volume (1.3 kg) and a low substrate-to-inoculum ratio (10:3 SIR). The results showed that an incorporation of accessible operational controls can effectively enhance cumulative methane yield (0.145 m3 CH4 kg−1 VS), corresponding to higher amounts of digestible organics converted. The calculated average volumetric methane productivity equalled 0.8802 L CH4 LWork−1 d−1 over 33.6 days whilst moderate pollutant removal (43.50% COD removal efficiency) was achieved. Molecular analyses identified Firmicutes and Bacteroidetes phyla as core organisms for hydrolytic and fermentative stages in trophic relationships with terminal electron acceptors from the methane-producing Methanosarcina genus. Economic projections established that the cost-effective operational enhancements were sustainable for valorisation from grape marc by existing wineries and distilleries.

Highlights

Grape is an economically significant fruit crop, with over 79 megatons (Mt) produced globally [1,2]
Based on the experiments conducted with grape marc, there was a cost-effective regulation of operational parameters such as inoculum sourcing, substrate-to-inoculum ratio, digester working volume, and hydraulic residence time, collectively impacting on the overall bioenergy production profile and the attainable remediation levels of winery residues
A fill-and-draw approach for digestate recirculation as an incoming downstream inoculum allowed for sufficient acclimation time between microbes and the substrate type, resulting in a shortened lag in subsequent treatment setups, reducing operating costs and increasing treatment efficiency

Summary

Introduction

Grape is an economically significant fruit crop, with over 79 megatons (Mt) produced globally [1,2]. An estimated 75% of the total grape production is crushed for winemaking [3]. At the end of fermentation, wine contains approximately 20% (w/v) of solid material, known as grape marc (GM) or pomace, which is produced at a rate of 2 t ha−1 [4,5,6]. After the primary grape juice has been extracted, the by-product (GM) is traditionally channelled to distilleries for additional valorisation. GM has been used as the raw material for the extraction of natural antioxidants, preservatives, and colouring agents for the food industry [7,8,9,10]

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Conclusion