Use of amaranth as feedstock for bio-ethanol production
The depletion of fossil fuel reserves and global warming are the two main factors contributing to the current demand in clean and renewable energy resources. Biofuels are renewable energy resources and have an advantage over other renewable resources due to biofuels having a zero carbon footprint and most feedstock is abundant. The use of biofuels brought about major concerns and these include food, water and land security. The use of lignocellulose as bioethanol feedstock can provide a solution to the food, water and security concerns. Biofuels such as bioethanol can be produced from lignocellulose by breaking down the structure of lignocellulose liberating fermentable sugars. Amaranth lignocellulose has a potential to be used as a feedstock for bioethanol production because amaranth plants has a high yield of biomass per hectare, require very little to no irrigation and have the ability to withstand harsh environmental conditions. The aim of this study was to investigate the viability of amaranth as a feedstock for bioethanol production by using alkaline assisted microwave pretreatment. Alkaline pre-treatment of amaranth using Ca(OH)2, NaOH and KOH at various concentrations (10-50 g kg-1 of alkaline solution in water) was carried out at different energy input (6-54 kJ/g). The pre-treated broth was enzymatically hydrolysed using Celluclast 1.5L, Novozyme 188 and Tween 80 at pH 4.8 and 50oC for 48 hours. The hydrolysate was further fermented to ethanol using Saccharomyces cerevisiae at a pH of 4.8 and 30oC for 48 hours. The effect of microwave pre-treatment on amaranth lignocellulose was evaluated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The monomeric sugars and ethanol were quantified using high performance liquid chromatography (HPLC). A maximum sugar yield of 0.36 g/g of biomass was obtained for pre-treatment with 30 g kg-1 Ca(OH)2 solution in water, 0.24 g/g of biomass was obtained for pre-treatment with 50 g kg-1 NaOH solution in water and 0.21g/g of biomass was obtained for pretreatment with 50 g kg-1 KOH solution in water at 32 kJ/g of energy input. After enzymatic hydrolysis the yields increased to 0.43 g/g, 0.63 g/g and 0.52 g g-1 of biomass for Ca(OH)2 , KOH and NaOH pre-treated biomass respectively. The highest ethanol yield obtained was found to be 0.18 g/g of biomass from fermentation of KOH pre-treated broth. The ethanol yield obtained from fermentation of Ca(OH)2 and NaOH pre-treated broth was 0.13 g/g of biomass and 0.15 g/g of biomass respectively. The results showed that an increase in concentration of alkaline solution and an increase in energy input liberate more sugars. A decrease in biomass loading was found to increase the total sugar yield. Pre-treatment with KOH was found to liberate more pentose sugars than the other alkaline solutions. The morphological changes shown by the SEM images showed that microwave irradiation is effective in breaking the structure of amaranth lignocellulose. The structural changes shown by the FTIR also validated that alkaline bases were effective in breaking the lignin, cellulose and hemicellulose linkages and liberating more sugars in the process. This work has demonstrated the enormous potential that amaranth lignocellulose has on being a feedstock for bioethanol production.
- Engineering