For decades in many markets across the country, tonnes of farm produce not sold are left to rot and waste. However, a team of researchers have found how such waste, specifically decaying oranges, can be converted to bio-ethanol which is a clean source of energy.
The research work is significant as the world begins to pay more attention to circular economy.
In their work titled, ‘Isolation and Characterisation of Ethanol-Tolerant Yeasts from Decaying Oranges for the Production of Bio-Ethanol,’ researchers Stella Adeyemo, Folake Afolabi, Kehinde Awojobi and Olayemi Ojo from the Microbiology Departments of Obafemi Awolowo University (OAU), Ile-Ife, and University of Ibadan (UI), Ibadan, Nigeria state that decaying orange fruits are readily available agricultural waste in Nigeria, yet they seem to be underutilized as potential growth medium for local yeasts strains, despite their rich carbohydrate content that can support yeast growth.
The ability of different strains of yeasts to grow on orange biomass and its utilization as raw material for the production of bio-ethanol was investigated in their study.
According to the researchers, five replicate samples of decaying oranges were collected at different time intervals from dump sites at five different local markets in Ile-Ife from which different species of yeasts were isolated. Standard biochemical tests were conducted to identify and confirm their identities.
A total of 30 yeast isolates were isolated and identified as Saccharomyces cerevisiae, Schizosaccharomyces japanicus, Candida valida, Candida Fructus, Candida krusei, Kluyveromyces africanus and Rhodotorula gramis.
Abundant production of bioethanol was derived from S. cerevisiae, C. Fructus and C. valida (C. Fructus and C. valida were used singly while C. fructus and Saccharomyces were combined in the ratio 1:1). The highest alcohol value (7.65 per cent) was derived from the mixed strain (Candida fructus and Saccharomyces cerevisiae).
According to Dr Adeyemo and her team, “Decaying oranges, its juice and its biomass could be used to produce bio-ethanol which is of good quality. The method is effective and efficient with high yield eco-friendly ethanol. The fruit waste provides readily available and cheap substrates for industrial use and at the same time solves the problem of environmental pollution that the decaying oranges cause if not disposed of appropriately.
“The use of fruit waste will not compete with wholesome oranges that are used as sources of vitamins and other nutrients in food which is a major concern when agricultural products are used for bio-ethanol production. Pre-treatment may not be necessary also.
“It has been observed over the years that bioethanol is suitable for use in machines, automobiles and other mechanical engines because it has less carbon (iv) oxide emission when in use. This is being done in Brazil, China and Italy.”
They added that “several authors have also regarded ethanol as fuel energy having carbon dioxide balances with ecological footprint which have the properties of renewable and sustainable energy.”