Evaluation of different glycerol fed-batch strategies in a lab-scale bioreactor for the improved production of a novel engineered ß-fructofuranosidase enzyme in Pichia pastoris.

The ß-fructofuranosidase enzyme from Aspergillus niger has been extensively used to commercially produce fructooligosaccharides from sucrose. In this study, the native and an engineered version of the ß-fructofuranosidase enzyme were expressed in Pichia pastoris under control of the glyceraldehyde-3-phosphate dehydrogenase promoter, and production was evaluated in bioreactors using either dissolved oxygen (DO-stat) or constant feed fed-batch feeding strategies. The DO-stat cultivations produced lower biomass concentrations but this resulted in higher volumetric activity for both strains. The native enzyme produced the highest volumetric enzyme activity for both feeding strategies (20.8% and 13.5% higher than that achieved by the engineered enzyme, for DO-stat and constant feed, respectively). However, the constant feed cultivations produced higher biomass concentrations and higher volumetric productivity for both the native as well as engineered enzymes due to shorter process time requirements (59 h for constant feed and 155 h for DO-stat feed). Despite the DO-stat feeding strategy achieving a higher maximum enzyme activity, the constant feed strategy would be preferred for production of the ß-fructofuranosidase enzyme using glycerol due to the many industrial advantages related to its enhanced volumetric enzyme productivity.

The effect of light emission spectrum on biohydrogen production by Rhodopseudomonas palustris.

Photofermentative hydrogen production has gained increasing attention as a source of green energy. To make such photofermentation processes economically competitive, operating costs need to be reduced, possibly through outdoor operation. Because photofermentation processes are light dependent, the emission spectrum and intensity of light both have a significant influence on the hydrogen production and merit investigation. This study investigates the effect of light sources on the hydrogen production and growth of Rhodopseudomonas palustris, comparing the organism's productivity under longer-wavelength light and light mimicking sunlight. Hydrogen production is enhanced under longer-wavelength light, producing 26.8% (± 7.3%) more hydrogen as compared to under light mimicking that of sunlight; however, R. palustris is still able to produce a considerable volume of hydrogen under light with a spectrum mimicking that of sunlight, providing a promising avenue for future research.

Modelling and testing of a light reflector system for the enhancement of biohydrogen production in a thermosiphon photobioreactor.

One of the main factors affecting hydrogen production and growth of photofermentative microorganisms is light; low light penetration and utilization are significant bottlenecks in photofermentative hydrogen production systems. In this study, light distribution in a thermosiphon photobioreactor operated with Rhodopseudomonas palustris was investigated. Radiation fields were modelled and simulated using computational fluid dynamics (ANSYS® Fluent, 2019 R2) and a reflector system was evaluated for the enhancement of light distribution in a thermosiphon photobioreactor. The effect of the reflector system was investigated experimentally in terms of hydrogen production, carbon substrate consumption and biomass circulation in the reactor. With the addition of the reflector system, hydrogen production was increased by 48% while glycerol consumption was increased from approximately 24% to 32%. After 336 h, the concentration of R. palustris cells still in suspension ranged from 0.13 to 0.18 g∙L-1, with no discernible difference in concentration between the systems with and without reflectors. Collectively, the reflector system was shown to be a viable option in enhancing light distribution in photobioreactors, with an associated increase in both hydrogen production as well as glycerol consumption.

The effect of diurnal light cycles on biohydrogen production in a thermosiphon photobioreactor.

Hydrogen production via microbial photofermentation shows great promise as a method for sustainable hydrogen production; however, operating costs associated with photofermentative hydrogen production need to be reduced. Costs can be reduced using a passive circulation system like the thermosiphon photobioreactor, and by operating it under natural sunlight. In this study, an automated system was implemented to investigate the effect of diurnal light cycles on the hydrogen productivity and growth of Rhodopseudomonas palustris and on the operation of a thermosiphon photobioreactor, under controlled conditions. Diurnal light cycles, simulating daylight times, were found to reduce hydrogen production in the thermosiphon photobioreactor demonstrating a low maximum production rate of 0.015 mol m-3 h-1 (± 0.002 mol m-3 h-1) as compared to 0.180 mol m-3 h-1 (± 0.0003 mol m-3 h-1) under continuous illumination. Glycerol consumption as well as hydrogen yield also decreased under diurnal light cycles. Nonetheless, hydrogen production in a thermosiphon photobioreactor under outdoor conditions was demonstrated as possible avenue for further investigation.

A Thermosiphon Photobioreactor for Photofermentative Hydrogen Production by Rhodopseudomonas palustris.

A thermosiphon photobioreactor (TPBR) can potentially be used for biohydrogen production, circumventing the requirement for external mixing energy inputs. In this study, a TPBR is evaluated for photofermentative hydrogen production by Rhodopseudomonas palustris (R. palustris). Experiments were conducted in a TPBR, and response surface methodology (RSM), varying biomass concentration, and light intensity and temperature were employed to determine the operating conditions for the enhancement of both hydrogen production as well as biomass suspension. Biomass concentration was found to have had the most pronounced effect on both hydrogen production as well as biomass suspension. RSM models predicted maximum specific hydrogen production rates of 0.17 mol m-3h-1 and 0.21 mmol gCDW-1h-1 at R. palustris concentrations of 1.21 and 0.4 g L-1, respectively. The experimentally measured hydrogen yield was in the range of 45 to 77% (±3.8%), and the glycerol consumption was 8 to 19% (±0.48). At a biomass concentration of 0.40 g L-1, the highest percentage of biomass (72.3%), was predicted to remain in suspension in the TPBR. Collectively, the proposed novel photobioreactor was shown to produce hydrogen as well as passively circulate biomass.