Page 386 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Bioenergy generation from agricultural wastes and enrichment of end products 349

butanol and ethanol are produced by fermentation process. Biobutanol is produced by
microorganism Clostridium spp. using sugar produced from different biomass (Li et al.,
2019). The process is known as acetone, butanol, and ethanol (ABE) fermentation that
comprises two stages of acedogenesis and solventogenesis (Ibrahim et al., 2018). In a
study, ABE production achieved from corn processing waste was 19.22 g/L that contained
the butanol yield of 11.65 g/L by using Clostridium beijerinckii SE-2 (Zhang and Jia,
2018). Biobutanol has higher heating value, lower volatility, less ignition problems, and
viscosity than bioethanol (Ibrahim et al., 2018). Beside these advantages, bioethanol is a
well-established technique than biobutanol due to less cost and high production yield than
biobutanol. Yeast, such as Saccharomyces cerevisiae, Candida albicans, Pichia stipitis,
and Kluyveromyces, are mostly used to generate bioethanol because of their high produc-
tivity .1 g/L/h and requirement of simple and inexpensive growth media (Azhar et al.,
2017). Basically, three fermentation techniques are used to generate bioethanol, separate
hydrolysis and fermentation, simultaneous saccharification and fermentation and simulta-
neous saccharification and cofermentation. The optimum temperature, pH, and agitation
speed range of fermentation are 20 C 35 C, 4 5, and 150 200 rpm, respectively, for

S. cerevisiae (Azhar et al., 2017). A yield of 11.6 g EtOH /g algae was achieved from fermen-
tation of industrial algae waste by using S. cerevisiae as fermentation microorganism
(Alfonsı ´n et al., 2019). Beside yeast, some facultative anaerobic genetically engineered
bacteria, such as Zymomonas mobilis, are also used for bioethanol production (Xia et al.,
2019).

Agricultural waste 1 ezymes ! Alcohol

15.5.2 Thermochemical conversion
These processes mainly comprise pyrolysis, gasification, and combustion that
require high temperature for the treatment of agricultural wastes into various useful
products, such as biooil, syngas, and biochar.

Pyrolysis is the thermal depolymerization of biomass in an inert atmosphere in continuous
supply of heat. It is an endothermic process and is performed in the temperature range of
400 C 700 C. The sources of substrate for biomass pyrolysis are agricultural wastes

(corn stover, corn cob, rice husk, wheat straw, etc.), woody biomass (redwood, pine,
beech, teak, etc.), energy crops (bamboo, sorghum, etc.), and also municipal solid wastes.
The rapid heating of biomass produces vapors that are the mixtures of various hydrocar-
bons and some part of it can be condensed to give an organic liquid called biooil (Gupta
and Mondal, 2019). Biooil is a brown colored viscous complex mixture of large number
of organic compounds with some amount of water content. It has the heating value in the
range of 20 30 MJ/kg and is also a source of valuable chemical compounds. However,
its properties can be enhanced after upgradation using various techniques. The noncon-
densable gas that leaves the system is a mixture of valuable gases (CO, CO 2 ,H 2 ,CH 4 ,
etc.). These gases have good combustion properties and can be used as gaseous fuel. The
remaining left-over residue is the carbon-rich compound called biochar. Biochar is a mul-
tifunctional material that can be used as solid fuel, adsorbent, sensor, fertilizer, etc.
However, product distribution in the pyrolysis process primarily depends upon the compo-
sitional analysis of biomass and on the interaction among them. It is also influenced by