Biomedical Engineering Reference
In-Depth Information
the gas supply is often not stable for as long as several months. Worse, some
digesters are damaged by frost. This situation has affected farmers' enthusiasm for
biogas seriously and is bad for the development of biogas. Currently, the technology
of biogas production in winter mainly involves heat preservation measures, heating
methods, the fermentation process, and bacterial cluster optimization [
108
].
(2) Diversity of raw materials
Currently, raw materials for biogas production are mainly human and animal
manure. The utilization of lignocellulose is relatively less. Therefore, on one hand,
improving the digestibility of lignocellulosic materials to increase gas production
is a method. On the other hand, based on local raw material characteristics,
regulating the substrate ratio, such as municipal solid waste, sludge, agricultural
waste material, and human and animal manure, and carrying out codigestion is
another method to alleviate the shortage of raw materials [
93
].
(3) Industrialization
Anaerobic fermentation technology for industrial organic wastewater treatment is
developing fast and is approaching the industrialization level, but the industrial-
ization for treating solid organic waste for energy production is still not mature.
Compared with other countries, anaerobic fermentation technology for treating solid
organic waste in China still falls behind. For example, the rate of gas production is
low, the maintenance and management levels are low, the technology and equipment
are not mature, the process of industrialization is slow, and so on [
96
].
6.4.5
Study of Lignocellulose Biogas Production
At present, substrates utilized in household biogas digesters in China are mainly
livestock manure. Thus, the shortage of raw material is a problem. On the other
hand, crop straw production in China reaches about 700 million tons annually, of
which rice straw, wheat straw, and cornstalks account for more than 70 %. If these
agricultural wastes can be utilized to produce biogas, not only the ecological envi-
ronment could be improved but also the energy shortage could be eased. Utilizing
lignocellulose to produce biogas has been studied, and the factors concerning the
rate of gas production, such as the pretreatment, enzymolysis, vaccination rate,
temperature, pH, size of particle, stirring style and rate, heavy metals, process,
and so on have been discussed. There are still some problems to be solved for
industrialization using lignocellulose to produce biogas, such as low gas production,
high cost of pretreatment, and ease of secondary pollution production. If these
problems could be solved, lignocellulose fermentation to biogas would have broader
prospects [
109
]. From the points of pretreatment and solid-state fermentation using
periodical stimulation, Chen and Li [
110
] proposed a new method using solid-
state fermentation to solve the difficulty in the treatment of fermentation residue,
to enhance the utilization of raw materials, and to increase gas production by
coupling with pretreatment. The main advantages of this method are as follows:
