Hydrogen Production from Coffee Mucilage in Dark Fermentation with Organic Wastes

Abstract

One of primary issues in the coffee manufacturing industry is the production of large amounts of undesirable residues, which include the pericarp (outer skin), pulp (outer mesocarp), parchment (endocarp), silver-skin (epidermis) and mucilage (inner mesocarp) that cause environmental problems due to toxic molecules contained therein. This study evaluated the optimal hydrogen production from coffee mucilage combined with organic wastes (wholesale market garbage) in a dark fermentation process. The supplementation of organic wastes offered appropriate carbon and nitrogen sources with further nutrients; it was positively effective in achieving cumulative hydrogen production. Three different ratios of coffee mucilage and organic wastes (8:2, 5:5, and 2:8) were tested in 30 L bioreactors using two-level factorial design experiments. The highest cumulative hydrogen volume of 25.9 L was gained for an 8:2 ratio (coffee mucilage: organic wastes) after 72 h, which corresponded to 1.295 L hydrogen/L substrates (0.248 mol hydrogen/mol hexose). Biochemical identification of microorganisms found that seven microorganisms were involved in the hydrogen metabolism. Further studies of anaerobic fermentative digestion with each isolated pure bacterium under similar experimental conditions reached a lower final hydrogen yield (up to 9.3 L) than the result from the non-isolated sample (25.9 L). Interestingly, however, co-cultivation of two identified microorganisms (Kocuria kristinae and Brevibacillus laterosporus), who were relatively highly associated with hydrogen production, gave a higher yield (14.7 L) than single bacterium inoculum but lower than that of the non-isolated tests. This work confirms that the re-utilization of coffee mucilage combined with organic wastes is practical for hydrogen fermentation in anaerobic conditions, and it would be influenced by the bacterial consortium involved.

Effect of Lignin Content on Cellulolytic Saccharification of Liquid Hot Water Pretreated Sugarcane Bagasse

“…In this work, we have demonstrated that even relatively small differences in lignin content can result in considerably increased sugar production, which supports the dissimilarity of bagasse lignin content and its effects on cellulose digestibility. The increased glucose yields with the addition of BSA helped to decrease the inhibition of non-productive absorption of cellulose enzymes onto lignin and solid residual lignin fractions.Molecules 2020, 25, 623 2 of 12 biofuel production [4,[6][7][8][9][10]. In particular, the physical barrier of lignin prevents enzyme access to cellulose and hemicellulose.…”

“…Molecules 2020, 25, 623 2 of 12 biofuel production [4,[6][7][8][9][10]. In particular, the physical barrier of lignin prevents enzyme access to cellulose and hemicellulose.…”

Modeling Dark Fermentation of Coffee Mucilage Wastes for Hydrogen Production: Artificial Neural Network Model vs. Fuzzy Logic Model

“…In order to analyze the anaerobic fermentative performance, two-level half-factorial experiments were designed through the Minitab 16 software program (Minitab 16, Minitab Inc., State College, PA, USA), following our previous study [13]. The resulting 26 sets were performed in a 20-L bioreactor with an actual working volume of 13 L. Raw coffee mucilage samples do not require any supplements, such as carbon/nitrogen nutrients and initial microbial culture, for transforming fermentable sugars in the substrate to hydrogen since there are appropriate nutrient sources, minerals, and microorganisms in the samples [13,19,20]. Our earlier work found that 7 species were isolated after anaerobic dark fermentation, and 4 species (Micrococcus luteus, Kocuria kristinae, Streptococcus uberis, and Brevibacillus laterosporus) were relatively highly involved and participated in hydrogen production.…”

“…Our earlier work found that 7 species were isolated after anaerobic dark fermentation, and 4 species (Micrococcus luteus, Kocuria kristinae, Streptococcus uberis, and Brevibacillus laterosporus) were relatively highly involved and participated in hydrogen production. Furthermore, increased hydrogen yield was observed when co-cultivation (bacterial consortium) was applied with K. kristinae and S. uberis, suggesting that the bacterial population could change the metabolic pathways and/or biochemical/molecular interactions that lead to efficient dark fermentation [13]. Briefly, a two-level factorial experimental test was designed with three different ratios (w/w) of coffee mucilage and organic wastes mixture (8:2, 5:5, and 2:8) were prepared, and additional control runs with only coffee mucilage or organic wastes were added [13].…”

“…Unlike the ANN, the fuzzy-logic-based model is applied for the predictive capacity without accurate knowledge of the process system and the interactions of the parameters [38]. Since a general fuzzy system converts numerical variables of the input and output into specified-level terms (high and low), the modeling of the anaerobic fermentative process is achievable for the prediction/development of the cumulative hydrogen yield under various types of substrate and interactions of the bacterial population [13,[39][40][41]. It is obvious that there is little to no literature for anaerobic fermentative hydrogen production from coffee mucilage combined with organic waste and its analytical modeling method.…”