Biobutanol - Biotechnology in China: Biofuels and Bioenergy - page 95

3 Progress in ABE Fermentation Process
3.1 Substrates
The main substrates for ABE fermentation in China include three kinds: starchy
feedstock (corn, cassava and potato), molasses and hydrolysate. In 2010, the total
yield of corn was 1.77 billion tons, according to the National Bureau of Statistics of
China. Currently, corn is the major substrate used in most of the ABE fermentation
plants in China. In addition to corn, corn starch (after removal of corn oil and protein)
is also used as the substrate in some plants [ 38 ]. The main strains used for
ABE fermentation in China are C. acetobutylicum-derived mutants, such as
C. acetobutylicum No. 2, C. acetobutylicum AS1.70 and C. acetobutylicum EA2018.
This species is preferabe for utilizing starchy feedstock as substrate for ABE
fermentation [ 25 ]. Besides starchy feedstock, molasses can also be used as low-cost
substrate in solvent fermentation. Molasses is a viscous by-product of the processing
of sugar cane or sugar beets into sugar. There are about 6 million acres of land under
cassava cultivation in Guangxi Province, with 8 million tons yield per year. The yield
of sugar cane and sugar beet in China is now more than 57 million tons and 6 million
tons, respectively. Fan et al. used sugar beet molasses for butanol production by fed
batch fermentation [ 12 ]. The concentrations of butanol and total solvents reached
14.15 and 19.65 g/L, respectively, with an over 70% ratio of butanol.
In contrast to the limited supply of starch and molassess, the abundant agricultural
residues can be a potential feedstock for ABE fermentation in China. It provides enough
feedstock for biobutanol production and avoids competition for food with an increasing
population. There is now great interest in exploring the hydrolysate of different lig-
nocellulosic substrates for ABE production all over the world. Nasib Qureshi [ 41 ]used
acid- and enzyme-hydrolyzed corn fiber as substrate for butanol production by
C. beijerinckii BA101. Wheat straw hydrolysate could also be utilized for ABE fer-
mentation [ 42 ]. In China, Li et al. [ 30 ] used enzymatic hydrolysis of steam-exploded
cornstalk stover for ABE production; the maximal butanol productivity reached
0.31 g/(L h). The hydrolysate of wheat bran was also used for ABE fermentation. The
C. beijerinckii ATCC 55025 used by Xu Ping's lab could produce a total of 11.8 g/L
solvent after 72 h fermentation of the hydrolysate of wheat bran [ 32 ]. Another new
hydrolysate is the acid hydrolysate of Jerusalem artichoke juice. Bai Fengwu's team
used Jerusalem artichoke juice as substrate; the final butanol titer reached 11.21 g/l [ 5 ].
Although lignocellulosic hydrolysates have been proved to be a potential substrate for
ABE fermentation, industrialization still needs more efforts from other fields, such as
the treatment of lignocellulosic materials, and an economic separation process.
3.2 Fermentation Process
The fermentation process mainly comprises batch fermentation, fed-batch fermen-
tation, continuous fermentation, cell immobilization, and fermentation coupled with