Design, implementation and assessment of a novel bioreactor for dark fermentative biohydrogen production.

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.