Hydrolisation of rice straw using microorganisms produced by garbage enzyme and compost tea for bioethanol production
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Date
2014
Authors
Rradakrishnan, Renuka
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Abstract
Lignocellulosic biomass can be utilized to produce bioethanol, a promising
sustainable energy as alternative for limited fossil fuel. There is a copious amount of
rice straw available in Malaysia that can be exploited for biofuel production. In order
to reduce cost and applying an environmental friendly method, compost tea solution
and garbage enzyme solution were examined as substitutes for acid hydrolysis of rice
straw. The present study involved pretreatment and hydrolysis of biomass, as well as
fermentation process. Pretreatment of rice straw to remove lignin can significantly
enhance the hydrolysis of cellulose. Optimization of enzyme loading also greatly
improves the hydrolysis. In order to expedite the process, different temperatures were
examined. Design Expert software Version 6.0.4 was used in aid to design the
experimental run. Different parameters were studied such as effect of pH,
temperature, and enzyme loading ratio. This study indicated that the optimum
condition for rice straw hydrolisation by compost tea was pH 5, 40 °C, 150 ml of
compost tea solution where most of the rice straw have been hydrolysed from
cellulose to fermentable sugar. Higher enzyme loading ratio gives a greater yield in
compost tea. Results showed that at pH 5, 40 °C, 150 ml of compost tea yielded the
highest fermentable sugars and ethanol; 3.59 ± 0.212 mg of fermentable sugars/g
substrate and 1.96 ± 0.207 mg ethanol/g substrate. While garbage enzyme solution
produces 1.88 ± 0.09 mg of fermentable sugars/g substrate and 0.817 ± 0.046 mg
ethanol/g substrate at pH 5, 40 °C, 50 ml. Enzyme activity of cellulase and xylanase
were determined in which compost tea solution produces the highest concentration of
cellulase activity of 3.97 ± 0.26 U/g substrate at pH 5, 55 °C and xylanase of 8.61 ±
0.295 U/g substrate at pH 9, 55 °C.
Concentration of cellulase and xylanase was very low in garbage enzyme solution
compared to compost tea solution. Compost tea solution produced the highest level
of fermentable sugar. These results indicate that selected substrates have great
potential for enzymatic hydrolysis.
Six types of bacteria were identified and isolated from both compost tea solution and
garbage enzyme solution. Carboxylmethylcellulose (CMC) Agar test was performed
to study on the ability of microorganisms present in compost tea solution and
garbage enzyme solution to breakdown cellulose. API (Analysis Profile Index) test
was conducted to further identify the species. Both temperature and pH influence the
outcome of a good yield of fermentable sugar. It is proven in this study that both
compost tea solution and garbage enzyme solution can be used as a natural substitute
for acid hydrolysis in bioethanol production.