296 • Impacts of Applied Genetics— Micro-Organisms, Plants, and Animals 
Figure l-D-3.— Alternative Schemes for Enzymatic Hydrolysis of Cellulosic Biomass for Ethanol Production 
Cellulosic 
biomass 
SOURCE: Massachusetts Institute of Technology. 
Table 1-0-1.— Alternative Pretreatment Methods for 
Lignocellulose Materials 
Chemical methods 
Physical methods 
Sodium hydroxide (alkali) 
Steam 
Ammonia 
Grinding and milling 
Chemical pulping 
Irradiation 
Ammonium bisulfite 
Freezing 
Sulfite 
Sodium chlorite 
Organic solvents 
Acids 
SOURCE: Office of Technology Assessment. 
veloped technology, such as that developed by 
groups working at Purdue University, New York Uni- 
versity, and Dartmouth College. There are several 
engineering problems involving both heat and mass 
transfer and acid/solvent recycle that need to be eval- 
uated at larger scale. At least some of this work will 
be done at the process development unit now being 
built at the Georgia Institute of Technology. The 
most promising directions that need de\ ('lopmeni 
are: 
• the scale-u|) of high ratcts and high yield labora- 
tory hydrolysis systems, and 
• the developnuMit of methods for acid and chem- 
ical recycle schttiiMfs. 
There are three ty|Hts of approaches that ha\e 
been employed for enzymatic Indrolysis of ( (“IIuIomc 
biomass. These artf summarized in figure l-D-.T They 
all involve some initial size reduction to increase the 
surface area available for enzymatic attack In 
schemes A and IT the incoming cellulosic hiom.tss i;» 
split into two streams; out' is used to grow organisms 
that produce cellulolytic enzymt's called eellul.isi-.'- 
and the other is used to produce sugar. 
In scheme A, tint eellulases are reeo\ cred and then 
added to a sc[)arate enzyme ludrohsis reat lion 
They hydi'olyztf both the cellulose and hemieellulosc. 
and the resulting sugar solution is then p.issed to an 
ethanol fermentation stage w hei e hexoses are eon 
verted by a yeast fermentation to ethanol I lili/alion 
of the ptfiilose ri'ciuires a separate lermenlalion lie 
