EFFECT OF FERMENTATIONON THE PRODUCTION OF BIOETHANOL FROM WATERHYACINTH, BREWERY SPENT GRAINS AND RICE STRAW

Abstract

In recent years, research has focused on the use of lignocellulosic biomers as an alternative source of bioenergy in a bid to combat the ongoing food crisis as well as the steady depletion of natural resources. This study evaluated the ability of Water hyacinth, Brewery spent grains (BSG) and Rice straw to produce bioethanol during fermentation with different isolated microorganisms. The three samples were dried and ground; and was subjected to chemical pretreatment and microbial hydrolysis to maximize sugar production. Standard methods were used to carry out isolation, identification and analysis of sample which includes proximate, mineral and physicochemical analysis. Each sample was fermented for seven days during which ethanol yield was determined. The microbial count obtained showed water hyacinth having the highest initial bacterial count of 7.10x107cfu/ml, while brewery spent grains had the initial lowest of 3.53x107cfu/ml. Rice straw was observed to have the highest final count after fermentation of 1.20x108cfu/ml. Water hyacinth showed relatively low amount of Lactic acid bacterial (LAB), having no growth as from day five. Fungal count on the other hand showed Brewery spent grains having the highest initial count of 5.5x107cfu/ml, while rice straw had the highest final count of 2.8x108cfu/ml.Organisms isolated from the fermentation of the substrates includes; Pseudomonas sp., Bacillus sp., Staphylococcus sp., Streptococcus sp., Micrococcus sp., Corynebacterium sp., Lactobacillus sp., Aspergillus sp., Penicilluim sp., Candida sp., Saccharomyces sp.and Trichoderma sp.with Bacillus sp.having the highest rate of occurrence. Cellulose hydrolysis screening carried out on each of the (16) tested isolates revealed T. viride having the highest clearance zone of 1.8cm, while those ofB. subtilis had the highest of 1.5cm in fungi and bacterial respectively.Proximate analysis obtained from the samples showed that the pretreatment method was relatively effective giving an increase in the cellulose and decrease in the hemicellulose and lignin contents of the samples. This showed rice straw having the highest overall cellulose of 51.33 ± 0.17% followed by Brewery Spent grains which had 45.80 ± 0.17% and water hyacinth having the lowest of 39.60 ± 0.17%. Potassium content was relatively high with Rice straw having the highest of 17.96mg/g, however calcium and sodium contents were relatively low in all the substrates with brewery spent grains having a high level of nitrogen of 3.72mg/g. Hydrolysis using T. viride gave higher reducing sugar yield than that obtained using B. subtilis with 21.2g and 10.18g respectively for Brewery Spent grains, 26.6g and 12.21g for rice straw and 18.55g and 8.22g for water hyacinth. The pH was observed to decrease during fermentation with rice straw having the overall lowest of 3.2 after seven days of fermentation using the natural flora, 4.2 when using T. viride and 4.7 when using B. subtilis, while Water hyacinth had the highest of 5.3, 5.2 and 5.9 respectively. Total titratable acidity observed showed an increase, ricestraw showed 2.4% after seven days of fermentation using the natural flora, 1.7% using B. subtilis and 0.8 using T.viride, Brewery spent grains showed 2.0%, 0.7% and 1.2% while water hyacinth had 1.8%, 0.3% and 0.3% respectively.Highest ethanol yield following fermentation with S. cerevisiae was given by Rice straw with a yield of 16.21g/100g, while Water hyacinth gave the lowest of 12.8g/100g, the ethanol yield from each substrate, were observed to be significantly different at p>0.05. The combined substrate showed the combination of rice straw and Brewery spent grains (1:1) giving the highest ethanol yield of 14.24g/100g, when using T. viride and S. cerevisiae, while water hyacinth had the highest of 3.02g/100g during natural fermentation. The study therefore showed that the substrates could be used for bioethanol production, with Rice straw being the most effective of the three substrates.