Abstract:
This study was designed to evaluate the production of bioethanol from Dioscorea rotundata
and Manihot esculenta peels using acid and alkaline pretreatments and fermenting with
monoculture of Zymomonas mobilis. Dioscorea rotundata peels was collected from garri
processing industry located at Shagari Village and Manihot esculenta peels was collected from
local vendors at South Gate, Akure, Ondo State Nigeria and transported to the Microbiology
Laboratory of Federal University of Technology, Akure for microbial analyses. Zymomonas
mobilis was isolated, characterized and identified from rotten sweet oranges using standard
biochemical methods. Isolation and characterization of microorganisms isolated from the peels
were carried out using standard microbiological techniques. Sulphuric acid and Sodium
hydroxide solution of 0.1 M each were used separately to pretreat the samples. Fermentation
process was allowed for 5 days. The fermented broth was distillated at 78ºC and the quantity
of bioethanol produced was measured. The total bacterial count was higher in Manihot
esculenta with 3.58 x 103 cfu/ml and total fungal count higher in Dioscorea rotundata with
3.01 x 103 sfu/ml. The carbohydrate content of dry and wet Dioscorea rotundata was higher
with values of 79.81 % and 79.78 % respectively, mineral composition of magnesium was
higher in Manihot esculenta with 15.64 mg and potassium was higher in Dioscorea rotundata
with 53.00 mg. pH of 7.37 was higher in neutralized wet Manihot esculenta in day 3,
neutralized pretreated wet Manihot esculenta produced higher reducing sugar of 8.99±0.01 g/l.
Changes in temperature was at 36ºC at the initial stage of fermenting wet and dry peels of
Dioscorea rotundata and Manihot esculenta, but later remained constant at 28 ºC till 120 hour
of fermentation. Cassava peels pretreated with 0.1 M of NaOH and neutralized (H2SO4
neutralized with NaOH) produced higher yields of bioethanol with (17.20 g/ml and 18.53 g/ml)
respectively. This study reveals the possibility of producing bioethanol from the fermentation
of Dioscorea rotundata and Manihot esculenta peels with the aid of Zymomonas mobilis which
serves as cheap alternative source of fuel and energy generation as well as a means of
controlling environmental pollution.
