Utilization of pineapple (Ananas comosus(L) Merr.) biomass for biofuel production

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Date
2014
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College of Agriculture, Vellayani
Abstract
A study on utilization of pineapple (Ananas comosus (L.) Merr.) biomass for biofuel production was conducted at College of Agriculture, Vellayani, Thiruvananthapuram during the period of 2013-14. Rising concern over depleting fossil fuel and greenhouse gas resulted in a high level of interest in nonconventional fuel originating from biorenewable sources including sugars, starches and lignocellulosic materials. Lignocellulosic materials constitute a substantial renewable substrate for bioethanol production that do not compete with food production and animal feed. Pineapple waste is a promising feed stock for alcohol production due to its abundance and ease of availability. Also it is a cheap substrate for biofuel production due to low lignin content and can undergo hydrolysis steps more easily. The feed stocks were prepared by drying and grinding of pineapple peel, pineapple fruit waste and pineapple plant residue separately. This is a method of physical pretreatment used for degradation of lignocelluloses and for reduction of cellulose crystallinity. The study on moisture content of the feedstocks using gravimetric method showed that pineapple plant residue has higher moisture content followed by pineapple fruit waste and pineapple peel waste. The estimation of sugar content of different feed stocks revealed that, pineapple fruit waste have highest values of glucose, fructose, xylose and sucrose compared to the other feed stocks and this higher levels of sugar content resulted in higher ethanol production during fermentation. Total dissolved solids was found to be maximum in pineapple fruit waste. Similarly total carbohydrate was recorded maximum in pineapple fruit waste followed by pineapple peel waste and lowest value was observed in pineapple plant residue. Estimation of cellulose, hemicelluloses and lignin content of the feed stocks revealed that pineapple plant residue have maximum cellulose content followed by pineapple fruit waste and pineapple peel waste. Whereas pineapple peel waste recorded maximum hemicellulose content. Lignin content was found maximum in pineapple fruit waste. To obtain a highly efficient conversion, pre treatment was performed for three feed stocks with acid and alkali which reduce the lignin content and make the sugar molecules accessible for fermentation. Acid and alkali pretreatment of the pineapple feed stocks resulted an increase in total reducing sugar and total non reducing sugar concentrations. The increase in sugar concentration in pretreated feedstocks is due to the hydrolysis of cellulose and hemicellulose in to sugars. The acid and alkali pretreatment decreased the lignin content, but a higher percentage removal of lignin was observed with alkaline pretreated pineapple feed stocks. The biochemical characterisation of the feed stocks revealed the sugar content and fermentation potential. To find out the effect of pretreatment fermentation was carried out in untreated and pretreated feed stocks with Saccharomyces cerevisiae and Zymomonas mobilis. Fermentation of untreated feedstocks gave higher alcohol percent than pre-treated feed stocks inspite of the fact that pretreatments resulted in an increase in total reducing and non reducing sugars and a decrease in the lignin content . This may be due to the production of various inhibitors or due to high salt formation during pH adjustments of the pretreated feedstocks. The results of percent conversion rate of reducing sugar to alcohol indicated that pineapple fruit waste have higher conversion rate than other feed stocks where as the percent conversion of non reducing sugar is found to be maximum with pineapple peel waste. pH of the fermenting medium also tend to become acidic. Characterisation of feedstocks and alcohol yield after fermentation showed that pineapple fruit waste is the most amenable feedstock for alcohol production than other two. The alcohol yield (8.34 per cent) obtained with untreated fruit waste using S.cerevisiae was found to be significantly higher than all other combinations tried. For the enhancement of fermentation and subsequent alcohol yield, cellulolytic microorganism was isolated from degraded pineapple waste. It was identified as Bacillus sp. by biochemical and molecular characterisation. Three modes of enhancement of fermentation were performed with pineapple fruit waste; Single batch bioconversion, simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) using Saccharomyces cerevisiae and isolated native microorganism. Single batch bioconversion was found to be the best enhancement method yielding 11.09 per cent alcohol. The decreased level of ethanol in other enhancement methods may be due to the negative interaction of Bacillus sp. with Saccharomyces cerevisiae. The present study concluded that fruit waste is the best candidate for bioethanol production than other pineapple feed stocks tried. Single batch bioconversion using the cellulolytic organism, Bacillus sp. and fermenting organism, S. cerevisiae could bring about a substantial enhancement in alcohol yield.
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