Patrick T. Sekoai

Biohydrogen production as a potential energy fuel in South Africa

Biohydrogen production has captured increasing global attention due to it social, economic and environmental benefits. Over the past few years, energy demands have been growing significantly in South Africa due to rapid economic and population growth. The South African parastatal power supplier i.e. Electricity Supply Commission (ESKOM) has been unable to meet the country’s escalating energy needs. As a result, there have been widespread and persistent power cuts throughout the country. This prompts an urgent need for exploration and implementation of clean and sustainable energy fuels like biohydrogen production in order to address this crisis. Therefore, this paper discusses the current global energy challenges in relation to South Africa’s problems. It then examines the feasibility of using biohydrogen production as a potential energy fuel in South Africa. Finally, it reviews the hydrogen-infrastructure development plans in the country.

Microbial cell immobilization in biohydrogen production: a short overview

Abstract The high dependence on fossil fuels has escalated the challenges of greenhouse gas emissions and energy security. Biohydrogen is projected as a future alternative energy as a result of its non-polluting characteristics, high energy content (122 kJ/g), and economic feasibility. However, its industrial production has been hampered by several constraints such as low process yields and the formation of biohydrogen-competing reactions. This necessitates the search for other novel strategies to overcome this problem. Cell immobilization technology has been in existence for many decades and is widely used in various processes such as wastewater treatment, food technology, and pharmaceutical industry. In recent years, this technology has caught the attention of many researchers within the biohydrogen production field owing to its merits such as enhanced process yields, reduced microbial contamination, and improved homogeneity. In addition, the use of immobilization in biohydrogen production prevents washout of microbes, stabilizes the pH of the medium, and extends microbial activity during continuous processes. In this short review, an insight into the potential of cell immobilization is presented. A few immobilization techniques such as entrapment, adsorption, encapsulation, and synthetic polymers are discussed. In addition, the effects of process conditions on the performance of immobilized microbial cells during biohydrogen production are discussed. Finally, the review concludes with suggestions on improvement of cell immobilization technologies in biohydrogen production.

Parametric Optimization of Citric Acid Production from Apple Pomace and Corn Steep Liquor by a Wild Type Strain of Aspergillus niger: A Response Surface Methodology Approach

In this work, parametric optimization of citric acid production (yield) from six process variables: apple pomace (AP) concentration, volume of corn steep liquor (CSL), pH, temperature, methanol concentration, and methanol addition time is reported. Fifty-four experiments were performed according to the Box-Behnken design method. A polynomial regression model was developed from the experimental data and effects of the variables were explained using response surface methodology approach. A coefficient of determination (R2) of 0.92 indicated the significance of the model. The optimum conditions for citric acid yield obtained from the model were 33.81 g/L of AP, 42.5 g/L of CSL, 2.05% (v/v) of methanol concentration, methanol addition time of 33 h, pH 4.54, and temperature of 32.88 °C with a corresponding yield of 62.00 g/L. Conducting an experiment using the optimum conditions gave citric acid yield of 68.26 g/L, a 10% increase over the model results.

Morphological modification of Chromolaena odorata cellulosic biomass using alkaline peroxide oxidation pretreatment methodology and its enzymatic conversion to biobased products

Abstract In this study, the structural modification of Siam weed (Chromolaena odorata) was performed using NaOH–H2O2- and Ca(OH)2–H2O2-based oxidative pretreatment for the enzymatic conversion of the biomass to a biocommodity, reducing sugar (RS). Pretreatment of raw sample was evaluated at temperatures of 60°C, 70°C, 80°C, 90°C for different time intervals of 3, 6, 9, 12 h in alkaline medium (NaOH or Ca(OH)2). The effects of pretreatment time and temperature were considered in obtaining the optimum conditions. The optimum conditions for NaOH–H2O2 was obtained at 70°C and 3 h with a maximum cellulose content of 44.29%(w/w), lignin content reduced to 21.09% from the initial raw value of 24.2%. Pretreatment with Ca(OH)2–H2O2 resulted in the optimum conditions obtained to be 70°C for 3 h with a cellulose content of 47.18%. Enzymatic hydrolysis on the pretreated biomass at the optimum conditions showed NaOH–H2O2-treated sample yielded 424.35 mg equivalent glucose/g biomass of RS while Ca(OH)2–H2O2-treated sample yielded 335.81 mg equivalent glucose/g biomass of RS. The untreated raw sample yielded 68.75 mg equivalent glucose/g biomass of RS. Consequently, NaOH–H2O2 pretreatment displayed a higher efficiency than Ca(OH)2–H2O2 pretreatment. Stereomicroscopic and scanning electron microscopic imaging of the treated and untreated samples revealed morphological disruptions brought about by the treatments.

Effect of metal ions on dark fermentative biohydrogen production using suspended and immobilized cells of mixed bacteria

ABSTRACT The effect of Fe2+, Mg2+, Ca2+, and Ni2+ ions on dark fermentative biohydrogen production was evaluated using suspended and immobilized cells of anaerobic mixed bacteria at different concentrations of 0, 50, 100, 300, 500, and 1,000 mg/L in batch operation. A maximum biohydrogen fraction of 45.21%, which corresponded to a biohydrogen yield of 292.8 mL H2/g total volatile solids, was obtained in batch process using Fe2+ (1,000 mg/L) and immobilized cells. Furthermore, a chemical oxygen demand removal efficiency of 52.30% was also achieved in this fermentation process.

Effect of nitrogen gas sparging on dark fermentative biohydrogen production using suspended and immobilized cells of anaerobic mixed bacteria from potato waste

ABSTRACT Biohydrogen is emerging as a suitable alternative to fossil fuels and has received worldwide popularity in recent years due to its economic, social and environmental benefits. This study was carried out to evaluate the effect of nitrogen gas sparging on dark fermentative biohydrogen production using suspended and immobilized cells of anaerobic mixed sludge. A maximum biohydrogen fraction of 56.98% which corresponded to a biohydrogen yield of 294.83 mL H2/g Total Volatile Solids (TVS) was achieved in a dark fermentation process using N2-sparged cells that were immobilized in calcium alginate beads. The biohydrogen production yield from the N2-sparged immobilized cells was 1.8 and 2.5 times higher than that of sparged suspended cells and non-sparged (control) suspended cells, respectively. Therefore, the synergistic effect of nitrogen gas sparging and cell immobilization was instrumental in inhibiting the biohydrogen-scavenging bacteria during the dark fermentation process, thereby enhancing the yield. These findings could pave the way for the development of a large-scale biohydrogen production process from biowaste feedstocks.