Biomedical Engineering Reference
In-Depth Information
The gas product is wood gas, whose main components are carbon dioxide, carbon
monoxide, methane, ethylene, and hydrogen.
In short, research of the thermochemical conversion of natural cellulose materials
has taken place since the 1940s. More than 100 research investigations on gasifica-
tion and thermal decomposition were performed in the United States from 1984
to 1990. However, studies in this area are still in the development stage and has
not yet industrialized. Generally, the requirements for thermochemical conversion
technology is high, and the cost is also high.
(3) Methane fermentation
Methane fermentation is the process of producing mixture gas mainly of methane
and carbon dioxide with the crop straw, livestock and human waste by microor-
ganisms under anaerobic conditions. Methane is used as a fuel for life; its thermal
efficiency is up to 60 %, six times higher than the thermal efficiency of straw direct
combustion. Biogas slurry and residues can be directly used for feed and high-
quality organic fertilizer. The calorific value of an ordinary methane fermentation
pool is about 22-25 MJ/m
3
(5,200-5,900 kcal).
It is a fundamental change in the fuels history of China and the world to utilize
straw and human and animal feces to produce biogas instead of firewood and coal.
Methane fermentation not only can solve fuel problems but also can expand the
source of feed and fertilizer, which is beneficial to the control of pests and diseases.
Methane fermentation technology has been applied widely. Enhancing the
fermentation of efficient bacteria and shortening the fermentation cycle need further
research in the future, which will help to explore the wide application of raw
materials and efficient bioreactor systems.
(4) Edible mushroom cultivation
Some edible fungi, such as oyster mushrooms, dried mushrooms, and other wood-
rotting and grass-rotting fungi that belong to the basidiomycetes of white-rot fungi,
have the strong decomposition ability of crude cellulose. They can directly use and
degrade cellulose, hemicellulose, and lignin in agricultural waste. Waste materials
from the harvested edible fungi fine fibers, especially lignin in them, can be greatly
reduced and thus can be directly used as feed additives. The equipment for edible
mushroom cultivation is simple, and raw materials are wide and cheap. Combining
the production of edible mushrooms and the improvement of straw feeding value is
important in rural areas in China [
20
]. Zhen studied the feasibility of the cultivation
of rare edible
Pleurotus geesteranus
in cornstalks; results showed that cottonseed
hull could be completely replaced by corn stovers to cultivate mushrooms, and
the biological efficiency was not significantly different. The biological efficiency
improved 10.47 % in cornstalks instead of sawdust. So, this method not only can
save wood but also is conductive to maintaining ecological balance [
21
]. Yao studied
the cultivation feasibility of
Flammulina velutipes
by rape straw stalks; the results
showed that the hyphae had the strongest growth with a substrate of 66 % rape straw,
22 % cottonseed hull, 10 % wheat bran, 1 % sucrose, and 1 % superphosphate. The
bud stage, the bud-pressing stage of the fruit body, and the fruiting period were all
shortened, which would increase economic efficiency [
22
].
