Optimization of fermentative parameters to improve hydrogen production: Is the co-fermentation of waste from the citrus agroindustrial an interesting alternative for energy recovery?

• Published in: Journal of environmental chemical engineering Vol. 11; no. 6; p. 111252
• Main Authors: Rocha, Danilo Henrique Donato, Sakamoto, Isabel Kimiko, Varesche, Maria Bernadete Amâncio
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2023
• Subjects: Calcium carbonate; Citrus peel waste; Citrus wastewater; Clostridium; Energy potential; Hydrogen; Organic acid; Clostridium; Energy potential; Citrus wastewater; Hydrogen; Organic acid; Calcium carbonate; Citrus peel waste
• ISSN: 2213-3437
• DOI: 10.1016/j.jece.2023.111252

The co-fermentation of peel and wastewater from citrus processing is a proposal to promote the complementation of the individual characteristics of these substrates, making it possible to obtain higher efficiency in hydrogen (H2) production, in addition to equating problems related to the logistics of destination and treatment of these waste. To build a model for optimizing hydrogen production, based on the variables of citrus peel waste concentration (9.9 – 35.1 gTVS.L-1), citrus processing wastewater concentration (0.3 – 8.7 gCOD.L-1), and calcium carbonate (CaCO3) concentration (0.3 – 7.3 g.L-1), the Rotational Central Composite Design and Response Surface Methodology (RSM) were applied, using a mesophilic granular sludge as inoculum for batch assays subjected to thermal treatment. Hydrogen production from 199.2 to 1241.9 mLH2.L-1 was obtained in the assays, with the lowest production obtained with 22.5 gTVS.L-1 of citrus peel waste, 4.5 gCOD.L-1 of citrus processing wastewater, and 0.3 g.L-1 of calcium carbonate, for a gCaCO3/gCarbohydrate ratio of 0.03. In the optimized condition with 21.4 gTVS.L-1 of citrus peel waste, 3.4 gCOD.L-1 of citrus wastewater and 4.5 g.L-1 of calcium carbonate, which resulted in a gCaCO3/gCarbohydrate ratio of 0.53, 1249.0 mLH2.L-1 were obtained. In the hydrogen optimized condition assay a relative abundance of 95% was observed for Clostridium Sensu Stricto 1, and therefore the Clostridial metabolic pathway was inferred as predominant, with a maximum butyric acid and acetic acid production of 2230.8 mg.L-1 and 1213.6 mg.L-1, respectively. For the lowest hydrogen production assay, there was a significant reduction in the Clostridium sensu stricto 1 (51.2%) abundance, and an increase in the Paraclostridium (20.0%) and Lactobacillus (21.9%) abundances, inferring lactic acid fermentation (6367.8 mg.L-1) as the predominant pathway. An energy potential of 523.2 MJ.t-1 of citrus waste was estimated based on the hydrogen production for the optimized condition assay. [Display omitted] •Intermediate substrate concentrations resulted in higher hydrogen production.•Low values for the Carbonate:Carbohydrate ratio resulted in negative effects on hydrogen production.•Clostridium sensu stricto 1 was identified in higher relative abundance in the hydrogen optimization condition.•Paraclostridium and Lactobacillus were identified for conditions with low hydrogen production.•The maximum hydrogen energy potential obtained met almost 10% of an industry's electricity demand.