Producing bioethanol from lignocellulosic materials by ruminal bacteria
Date Issued
2009
Date
2009
Author(s)
Huang, Ai-Lan
Abstract
Because of the depletion of the fossil fuel reserve, it has attracted great attention in the renewable energy resources around the world. Bioethanol is one of the most promising alternative energy resources. Nowadays, most bioethanol is produced from sugarcane and corn. However, these materials are also provided as food for human or animals. Therefore, it will cause a competitive threat, resulting in high-rised price. Currently, lignocellulosic materials are considered as potential substitutes. They include agricultural residues, forestry residues and dedicated energy crops. Difficulty of hydrolysis is the major barrier of bioethanol production from lignocellulosic material. Directly hydrolyzing the biomass and fermenting to ethanol by ruminal bacteria may provide an alternative way for the bioethanol production from recalcitrant lignocellulosic materials.n this study, silvergrass, rice straw and soybean hull were used as substrates to produce ethanol by coculture of ruminal cellulolytic bacteria Ruminococcus albus 7 with one of major ethanol producers in rumen Treponema saccharophilum PB or Lachnospira multiparus D32. Samples from coculture incubation were harvested at 0, 4, 8, 12, 24, 36 and 48 h for measurements of dry matter digestibility, pH value, reducing sugar concentration and ethanol concentration.hen R. albus 7 was cocultured with T. saccharophilum PB, substrates’ DM digestibility increased markedly from 0~8 h, then slowed down after 8 h. At the same time, the pH values decreased from 0~8 h along with the dramatical decrease of total reducing sugar concentrations. Afterwards, total reducing sugar concentration remained fairly constant, indicating sugar produced by cellulolytic bacteria was consumed by saccharolytic bacteria instantly. Concentrations of ethanol reached a maximum between 8 and 12 h and then remained fairly constant. When R. albus 7 was cocultured with L. multiparus D32, the substrates’ DM digestibility and reducing sugar concentration had a similar change pattern as R. albus 7 with T. saccharophilum PB. However, ethanol production increased to a maximum before 24 h and then decreased by time. Although soybean hull had the greatest digestibility in both coculture experiments, the ethanol yield was no significantly different from other two substrates by R. albus 7 and T. saccharophilum PB coculture, and the greatest ethanol yield was achieved with silvergrass by R. albus 7 and L. multiparus D32 coculture. Additionally, when adding 25 μM 3-phenylpropanoic acid (PPA), both of the DM digestibility of silvergrass and the yield of ethanol increased significantly in the coculture of R. albus 7 and T. saccharophilum PB (P < 0.05). In conclusion, mixed ruminal bacteria can produce bioethanol from lignocellulosic materials rapidly. However, different materials were suitable for different microorganisms to utilize. In addition, adding PPA can significantly improve substrate digestibility and ethanol yield for harsh lignocellulosic materials.
Subjects
lignocellulosic material
ruminal bacteria
bioethanol
SDGs
Type
thesis
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