Optimization of key factors affecting hydrogen production from coffee waste using factorial design and metagenomic analysis of the microbial community

The objective of this study was to evaluate the fermentation conditions that led to the optimization of H-2 production from coffee waste (wastewater, pulp and husk) and the taxonomic and functional characterization of autochthonous microorganisms. Assays in batch reactors with microbial consortium bioaugmentation (bacteria and fungi) evaluated the pH (4.82-8.18), pulp and husk concentration (6.95-17.05 g/L) and headspace factor (33.18-66.82%) by means of rotational central composite design and response surface. Operating conditions in the reactor optimized for 3.04 LH2/Ld were at pH 7.0, 7 g/L pulp and husk and 30% headspace. The main metabolites observed were butyric acid (3838 mg/L), isobutyric acid (506 mg/L), methanol (226 mg/L) and butanol (156 mg/L). Clostridium sp. (87.9%), Lactobacillus sp. (1.7%), Kazachstania sp. (18.6%) and Saccharomyces sp. (16.3%) were the main genera identified in the optimized reactor, which had functional gene diversity for H-2 production, alcoholic fermentation, cellulose degradation, lignin, hemicellulose and phenol. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.