Abstract
The goal of this study was to evaluate the use of expanded clay as a support material for Thermoanaerobacterium thermosaccharolyticum KKU19 to produce hydrogen from oil palm trunk hydrolysate (OPT) and slaughterhouse wastewater (SHW) in a fixed-bed reactor (FBR) under non-sterile conditions. The effects of hydraulic retention time (HRT) on the performance of the FBR were also investigated. The FBR was operated at an OPT hydrolysate to SHW ratio of 2.55:1 (v:v), 60°C, initial pH 6.5, and 1.2 mg (as total volatile solids/g expanded clay) of T. thermosaccharolyticum KKU19 immobilized on expanded clay. A maximum hydrogen production rate (HPR) and hydrogen yield (HY) of 7.15 ± 0.22 L/L day and 234.45 ± 5.14 mL H2/g-COD, respectively, were obtained at an HRT of 6 h. Long-term operation of FBR at 6 h HRT indicated that expanded clay efficiently immobilizes T. thermosaccharolyticum KKU19, for which an HPR of 6.82 ± 0.56 L H2/L day, and an HY of 231.99 ± 19.59 mL H2/g-COD were obtained. Furthermore, the COD removal efficiency of 30% obtained under long-term operation was comparable to that under short-term operation at an HRT of 6 days. Butyric and acetic acids were the main soluble metabolite products, thereby indicating a butyrate–acetate type fermentation. Our findings indicate that expanded clay is an effective support material that contributes to the protection of microbial cells and can be used for long-term operation.
Highlights
The depletion of fossil fuels and severe environmental problems, global warming, have driven the search for alternative energy sources (Vasiliadou et al, 2018; Kumar et al, 2019; Shetty et al, 2019)
The goal of the present study was to evaluate the use of expanded clay as a support material for T. thermosaccharolyticum KKU19 to produce hydrogen from oil palm trunk hydrolysate (OPT) hydrolysate co-digested with slaughterhouse wastewater (SHW) in an fixed-bed reactor (FBR) under non-sterile conditions
The co-digestion of OPT and SHW provided a balanced ratio of carbon to nitrogen which could enhance the production of hydrogen
Summary
The depletion of fossil fuels and severe environmental problems, global warming, have driven the search for alternative energy sources (Vasiliadou et al, 2018; Kumar et al, 2019; Shetty et al, 2019) In this regard, hydrogen fits the bill perfectly, given its environmentally friendly characteristics, with water being the only by-product generated as a consequence of combustion with oxygen. The hydrogen yield (HY) attained by dark fermentation can be enhanced by increasing hydrogen production through an acetic acid end-product reaction and by reducing or preventing butyric acid, lactic acid, and ethanol endproduct reactions (O-Thong et al, 2008). Such modifications can be accomplished by operating a high-temperature fermentation process at temperatures greater than 60◦C using thermophilic microorganisms as hydrogen producers. It has been found that high temperatures increase the rate of biochemical processes, resulting in higher HY and fewer varieties of fermentation end-products than under mesophilic conditions (Prasertsan et al, 2009)
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