Optimization of fermentative parameters to improve hydrogen production: Is the co-fermentation of waste from the citrus agroindustrial an interesting alternative for energy recovery?
Danilo Henrique Donato Rocha, Isabel Kimiko Sakamoto, Maria Bernadete Amâncio Varesche
Abstract
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 (H 2 ) 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 (CaCO 3 ) 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 mLH 2 .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 gCaCO 3 /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 gCaCO 3 /gCarbohydrate ratio of 0.53, 1249.0 mLH 2 .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.