Abstract
This study focused on the possibility of improving fermentative hydrogen and methane production from an inhibitory fruit-flavored medium using polyvinylidene fluoride (PVDF) membrane-encapsulated cells. Hexanal, myrcene, and octanol, which are naturally produced in fruits such as apple, grape, mango, orange, strawberry, and plum, were investigated. Batch and semi-continuous fermentation processes at 55 °C were carried out. Presence of 5 g/L of myrcene, octanol, and hexanal resulted in no methane formation by fermenting bacteria, while encapsulated cells in the membranes resulted in successful fermentation with 182, 111, and 150 mL/g COD of methane, respectively. The flavor inhibitions were not serious on hydrogen-producing bacteria. With free cells in the presence of 5 g/L (final concentration) of hexanal-, myrcene-, and octanol-flavored media, average daily yields of 68, 133, and 88 mL/g COD of hydrogen, respectively, were obtained. However, cell encapsulation further improved these hydrogen yields to 189, 179, and 198 mL/g COD. The results from this study indicate that the yields of fermentative hydrogen and methane productions from an inhibitory medium could be improved using encapsulated cells.
Highlights
Increasing energy demand and the depletion of fossil fuel reserves, coupled with global warming, have stimulated a rapid growth in developing alternative energy sources that are sustainable, renewable, and environmentally friendly
Since fermentative hydrogen is a precursor for methane production, it is likely that hydrogen production could be limited by fruit flavors
The major barriers associated with the widespread applications of fermentative hydrogen and methane as fuels include, among others, the low yields of the gas production
Summary
Increasing energy demand and the depletion of fossil fuel reserves, coupled with global warming, have stimulated a rapid growth in developing alternative energy sources that are sustainable, renewable, and environmentally friendly. Energy carriers such as hydrogen and methane have been suggested as good substitutes for fossil fuels. The dark fermentation process is characterized by low hydrogen yield, which affects methane production. This phenomenon has been attributed to factors such as substrate and product inhibitions, environmental and operating parameters, or the tendency of the fermentation process to result in biomass production. Some fermentative feedstocks often contain inhibitory compounds that tend to inhibit the feedstock degradability by anaerobic microorganisms
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