Browsing by Author "Ross, Brandon Sean"

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    The effect of light intensity and reactor configuration on Rhodopseudomonas palustris growth and hydrogen production
    (Stellenbosch : Stellenbosch University, 2024-03) Ross, Brandon Sean; Pott, Robert William McClelland; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ANGLISH ABSTRACT: Biological hydrogen production is a promising replacement for the current modes of hydrogen production seen in industry today. However, key issues with the process still need to be solved, such as its economic viability and whether environmentally sustainable production is possible. The use of photosynthetic bacteria such as the purple non sulphur bacterium Rhodopseudomonas palustris to produce hydrogen via photofermentation has shown to have a low environmental impact but the required energy input is greater than the energy derived from the hydrogen produced. To increase the efficiency of the hydrogen production process the ratio of energy consumed to energy produced must be improved. One method of enhancement is the design and development of photobioreactor (PBR) systems to improve the hydrogen production of the process. The majority of PBRs have been designed for microalgae systems, with very few reactors designed for photosynthetic bacteria. PBR designs are therefore required to improve the hydrogen production of bacterial systems. Outdoor operation has also been earmarked as a means to improve the economic viability of the process as the required light energy will be provided by sunlight, which is a free source of light energy. However, the effect of light intensity on the growth of R. palustris is fairly poorly understood. The aim of this study was to determine the effect of light intensity on the growth of R. palustris, and to design and construct a multipurpose PBR that can be used for the cultivation of planktonic and immobilised R. palustris to produce biological hydrogen. The first objective was to compare the effect of changing light intensity on the growth kinetics of R. palustris. The results of this comparison showed that R. palustris grows readily over the range of light intensity investigated (70 to 600 W/m2 ), with photo-limitation occurring at low intensities (30 and 70 W/m2 ), photosaturation occurring between 200 and 400 W/m2 , and photo-limitation occurring when the light intensity increased to 600 W/m2 . The highest maximum specific growth rate of 0.0420±0.014 h-1 was achieved at a light intensity of 400 W/m2 . A predictive model for the cell growth and substrate utilisation of R. palustris over the range of light intensity investigated (70 to 600 W/m2 ) was successfully developed with the model showing good fit to the experimental data. A PBR that facilitated hydrogen production by R. palustris either as a growing planktonic cell culture or immobilised in a PVA cryogel matrix was successfully designed and constructed. The performance of the PBR operating with planktonic cells was compared to immobilised cells operating as a fluidised bed PBR (FBPBR) and a packed bed PBR (PBPBR). The FBPBR achieved the highest maximum specific hydrogen production rate of 15.74±2.2 mL/g/h. The planktonic culture and PBPBR achieved lower production rates of 12.6±8.0 mL/g/h and 4.53±0.8 mL/g/h respectively. In terms of the substrate conversion efficiency, the FBPBR achieved a conversion of 43% which outperformed the PBPBR which only achieved a conversion of 26.7%. The conversion efficiency of the planktonic cell culture was between the two immobilised cell configurations with an efficiency of 32%.