Design, implementation and assessment of a novel bioreactor for dark fermentative biohydrogen production.
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Date
2020
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Abstract
The majority of the world’s energy consumption and electricity generation is derived
from fossil fuel sources. Their consumption has a negative environmental impact, thus
the need for renewable energies. Hydrogen being a high energy zero carbon fuel
source presents a profound appeal. Hydrogen may be produced biologically via
various methods, this work involves dark fermentative hydrogen production (DFHP).
A review of literature on the physicochemical parameters affecting fermentative
hydrogen bioprocess was conducted. Bioreactor design was identified as a
fundamental component that regulates the overall process outcome and was therefore
analysed at length. The review highlighted that existing reactor configurations are
unable to sustain a comprehensive criteria of efficient DFHP. A consolidation of
biomass retention and non-invasive agitation were distinguished as crucial. The need
for a novel reactor configuration possessing these attributes was consequently
accentuated.
This study focuses on the design, implementation and assessment of novel bioreactor
configuration for DFHP. The vessel was formed from a 2L glass and fitted with ports.
Three 3D-printed permeable cartridges enclosed immobilized microbial cells and
functioned as baffles. The localization and motion of the cartridges promoted improved
exposure between microbial cells and substrate. Agitation was accomplished by
rocking the vessel at 180°. All the control set points were adjustable, presenting the
option of evaluating diverse control regimes. The implemented reactor showed a 35%
increase in the peak hydrogen fraction and a 58% reduction in lag time compared to
the control shake flask reactor. These findings showed that the novel reactor
configuration, by means of the cartridge structure supporting the immobilized cells,
enhanced the biohydrogen production process.
Subsequently, a preliminary scale up of the cartridge concept was implemented and
incorporated into a continuous stirred tank reactor (CSTR). The cartridge
(46x40x300mm) consisted of perforated hollow rectangular tubes, joined to form a single amalgamation. This unit was used as substitute for the standard impellers of
the CSTR and aligned at 120° laterally to the agitating shaft. The modified reactor
prepared with Immobilized cells in cartridge (ICC) was comparatively assessed with
the standard CSTR operated with suspended cells in reactor (SCR) and immobilized
cells in reactor (ICR). ICC reduced fermentation time by 52 and 65% compared to
SCR and ICR respectively. Gompertz model coefficients indicated a 98 and 37%
increase in the maximum hydrogen production rate (Rm) using the ICC compared to
the SCR and ICR fermentations respectively. ICC also showed better pH buffering
capacity and complete glucose degradation. These findings further demonstrated that
the scale up reactor configuration with the cartridge structure improved biohydrogen
productivity, yield and process economics.
The novel configuration reduced process time, improved Hydrogen yield and ensured
complete substrate degradation. Furthermore, the structural integrity of immobilized
cells was maintained. These findings demonstrated that the novel bioreactor design
improved biohydrogen production and showed potential for further DFHP research and
development.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.