Optimization of biohydrogen production inoculum development via hybrid pre-treatment techniques : semi pilot scale production assessment on agro waste (potato peels)
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Date
2015
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Abstract
The challenges of energy crisis and environmental pollution are vital issues hindering the
global sustainable development as a result of over dependence on fossil fuels. These are
driving the need to explore renewable and environmentally friendly energy sources.
Biohydrogen has emerged as an eco-friendly renewable energy source and a suitable
alternative to fossil fuels. However, the commercialization of biohydrogen energy is hindered
by the high production cost and low yield which necessitates novel strategies for an
economically feasible production.
Some of these strategies include the development of stable inoculum, scale-up studies, and
the utilization of renewable feedstock such as agro-food waste materials which are both
abundant and sustainable. Inoculum pre-treatment is a vital aspect of hydrogen production
technology as it contributes to the improvement of hydrogen yield. The inoculum
pre-treatment method influences the community structure which in turn affects the microbial
metabolism of hydrogen production.
This study investigates novel inoculum development techniques and evaluates the feasibility
of biohydrogen production from agro waste (potato peels). The linear and interactive effect of
these techniques on inoculum efficiency as well as the key process parameters for hydrogen
production from potato peels were modelled and optimized. Further assessment of the
hydrogen production dynamics at the semi-pilot scale including the microbial community
structure were investigated using the 16SrRNA gene clone library sequence analysis.
A hybrid inoculum development technique of pH and Autoclave (PHA), pH and Heat shock
(PHS) was modelled and optimized using the response surface methodology. The quadratic
polynomial models had a coefficient of determination (R2) of 0.93 and 0.90 and the optimized
pre-treatment conditions gave a 37.7% and 15.3% improvement on model predictions for
PHA and PHS respectively. Maximum hydrogen yield of 1.19 mol H2/ mol glucose was
obtained for PHA in a semi-pilot scale process.
The interactive effect of a hybrid pH and microwave pre-treatment on mixed inoculum for
biohydrogen production was investigated. The obtained model had a coefficient of
determination (R2) of 0.87. Two semi pilot scale-up processes were carried out to assess the
efficiency of the developed inoculum with and without pH control on biohydrogen
production. A two fold increase in glucose utilization was obtained and a molar hydrogen
yield of 2.07 mol H2/mol glucose under pH controlled fermentation compared to 1.78 mol
H2/mol glucose without pH control. Methane production was not detected which suggests the
effectiveness of the combined pre-treatment to enrich hydrogen producing bacteria.
The developed inoculum was used to evaluate the feasibility of biohydrogen production from
potato peels waste. The key process parameters of substrate concentration (g/L), nutrient
supplementation (%), temperature (°C) and pH were modelled and optimized using the
Artificial Neural Network (ANN) and Response surface methodology (RSM). The optimum
conditions obtained were 50g/L of potato waste, 10% nutrients, 30°C and pH 6.5. A semi
pilot production process under the optimized condition gave a hydrogen yield of 239.94mL/g
TVS corresponding to a 28.5% improvement on hydrogen yield. Analysis of the microbial
community structure showed the dominance of the genus Clostridium comprising of about
86% of the total microbial population including C. aminovalericum, C. intestinale, C. tertium,
C. sartagofome, C. beijerinckii and C. butyricum in ascending order of predominance. Hydrogen consuming methanogens were not detected which further confirmed the efficiency
of the hybrid inoculum pre-treatment.
This study has highlighted the development of a novel hybrid inoculum pretreatment method
to establish the requisite microbial community and to safeguard the stability of biohydrogen production. Furthermore, the potential of generating an economical feasible biohydrogen
production process from potato waste was demonstrated in this work.
Description
Doctor of Philosophy in Microbiology.
Keywords
Potato waste., Plant inoculation., Sustainable development., Fossil fuels., Theses -- Microbiology.