An Evaluation of the Global Potential of Cocoyam (Colocasia and Xanthosoma species) as An Energy Crop

Abstract

Aims: To evaluate the potential of cocoyam (Colocasia and Xanthosoma species) for the production of ethanol and methane for use as energy sources. Study design: Laboratory experimentation. Place and duration of study: Federal College of Agriculture Ibadan and Institute of Agricultural Research and Training (IAR&T), Moor Plantation, Ibadan, Nigeria between December 2010 and June 2011. Methodology: Five, 15, 25 and 35 kg samples of peeled cocoyam corms were weighed in three replicates. Next, the weighed cocoyam was soaked in clean water for 24 hr, and afterwards placed on a clean tray and allowed to air dry naturally for 4 hr. The cocoyam corms were then cut and the pieces transferred to a mortar where they were mashed to attain sufficient size reduction. The mash was then transferred into a plastic bucket. Five hundred, 650, 800 and 950 ml of N-hexane (C6H14) was added to the 5, 15, 25 and 35kg samples. The mash was thoroughly stirred to achieve an even mixture with the hexane. It was then covered and left undisturbed in the laboratory at room temperature for 8 days. The fermented mash was poured onto a 0.6 mm aperture size sieve and completely squeezed to dryness while the liquid filtered through the sieve. N-hexane was removed from the filtered liquid. The collected liquid was poured into a glass dish and then gradually heated at 79°C for a total of 10 hr (at intervals of 2 hr heating followed by 1 hr cooling) to ensure complete evaporation of any trapped H2O or CO2 remaining in it. Afterwards the final liquid (ethanol) was allowed to cool normally in the lab and its mass, volume and other properties were measured. Results: It was found that ethanol was yielded at the rate of 139 L/tonne of cocoyam. Therefore, 10 million tonnes annual global production of cocoyam is potentially able to produce 331 million gallons of ethanol (i.e. 200 million gallons gasoline equivalent) or 39.5 million cubic metres of methane which on burning would produce 179.3 x 107 MJ of energy. The mash obtained as byproduct of the processes is capable of supplying 59 calories of food energy per 100g.  Conclusion: Cocoyam has very good potential as a source of ethanol and methane. Its use as a renewable source of energy for the production of biofuels is recommended and doing so poses no threat to the environment or food supply. The mash produced is an excellent feedstock for livestock. The scientific innovation and relevance of this study lies in the fact that cocoyam is a renewable produce and the fermentation and anaerobic digestion methods used are applicable across countries and regions irrespective of available degree of industrialization and climate.