Abstract
Bioethanol as a fossil fuel additive to decrease environmental pollution and reduce the stress of the decline in crude oil availability is becoming increasingly popular. This study aimed to evaluate the concentration of bioethanol obtainable from fermenting cashew apple juice by the microorganism Saccharomyces cerevisiae Y2084 and Vin13. The fermentation conditions were as follows: initial sugar = 100 g/L, pH = 4.50, agitation = 150 rpm, temperatures = 30°C (Y2084) and 20°C (Vin13), oxygen saturation = 0% or 50%, and yeast inoculum concentration = ~8.00 Log CFU/mL. The maximum ethanol concentration achieved by Y2084 was 65.00 g/L. At 50% oxygen the fermentation time was 5 days, whilst at 0% oxygen the fermentation time was 11 days for Y2084. The maximum ethanol concentration achieved by Vin13 was 68.00 g/L. This concentration was obtained at 50% oxygen, and the fermentation time was 2 days. At 0% oxygen, Vin13 produced 31.00 g/L of ethanol within 2 days. Both yeast strains produced a higher glycerol concentration at 0% oxygen. Yeast viability counts showed a decrease at 0% oxygen and an increase at 50% oxygen of both yeast stains. Other analyses included measurement of carbon dioxide and oxygen gases, process monitoring of the fermentation conditions, and total organic carbon. Gas analysis showed that carbon dioxide increased in conjunction with ethanol production and oxygen decreased. Process monitoring depicted changes and stability of fermentation parameters during the process. Total organic carbon analysis revealed that aerobic fermentation (50% oxygen) was a more efficient process as a higher carbon recovery (95%) was achieved.
Highlights
The twenty-first century is plagued by difficulties like the decrease in resources of fossil fuel, rapid rise in greenhouse gas emissions contributing to global warming, and the lack of capability to meet the increasing energy demands
For this research cashew apples were obtained from Coastal Cashews located in the KwaNgwanase region in Northern KwaZulu Natal, South Africa
Even though the ethanol concentration achieved by Y2084 was lower, the advantage is, Y2084 is not dependent on oxygen for its activity
Summary
The twenty-first century is plagued by difficulties like the decrease in resources of fossil fuel, rapid rise in greenhouse gas emissions contributing to global warming, and the lack of capability to meet the increasing energy demands. In trying to reduce the impact of these global concerns, bioethanol produced from renewable resources like biomass components has created significant interest. Bioethanol production is a three-stage process of: (i) hydrolysis, (ii) fermentation and (iii) distillation [2]. Distillation is a thermochemical separating process that concentrates ethanol to 95%, depending on the difference in boiling points between substrates during heat application [1, 2]. This biologically derived product is an ethyl alcohol that can be used as a petroleum alternative or additive
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