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374 Refining Biomass Residues for Sustainable Energy and Bioproducts

16.3.4 Pyrolysis process for production of biochar

In pyrolysis systems, agroindustry waste is generally heated under certain condi-
tions of temperature, nitrogen flow rate, etc. in the absence of oxygen for vaporiza-
tion of the material, leaving a char behind. This is considered to be a higher
technology procedure for the utilization of agricultural wastes. Others are hydroga-
sification and hydrolysis. They are used for the preparation of chemicals from agri-
cultural waste as well as for energy recovery. Of particular interest to agriculture
are the preparation of alcohols for fuel, ammonia for fertilizers, glucose for food
and feed. Pyrolysis of agricultural waste yields oil, char, and low heating value gas.

16.3.5 Direct combustion

The simplest and traditional way to utilize agroindustry waste is to burn it for the
production of fuel. The process of combustion of agroindustry waste “consists of
the rapid chemical reaction (oxidation) of biomass and oxygen, the release
of energy, and the simultaneous formation of the ultimate oxidation products of
organic matter CO 2 and water” (Klass, 2004). The energy is released mostly in
the form of radiant/thermal energy under sufficient rate of oxidation. Fabrication of
agricultural waste in solid form needs to be done for its efficient utilization through
thermal conversion. Agroindustry waste is usually burnt for various purposes such
as cooking, production of charcoal, steam generation, mechanical applications, and
electric power applications. Due to its lower cost, the direct combustion still
accounts for the dominant technology (Klass, 2004).

16.4 Suitability of the wastes for various processes

There are different types of processes available for conversion to value-added pro-
ducts. The physiochemical properties of value-added products would obviously
depend not only the processing conditions (temperature, etc.) but also on the physi-
cal and chemical composition of waste (Tables 16.6 16.8). Ravindran et al. (2018)
assessed the suitability of different types of agricultural wastes (sugarcane bagasse,
corn cob, and rice bran) for the production of enzymes using SSF. The difference in
physical chemical nature of these substrates would influence their ability to pro-
duce xylanase. It was found from their study that the pretreatments of such sub-
strates would increase their efficiency in SSF process.
Other than SSF, even for the production of biochar using pyrolysis, the suitabil-
ity of waste needs to be looked upon carefully. Lo ´pez-Cano et al. (2018) analyzed
the suitability of organic wastes such as from holm oak, greenhouse wastes, green
wastes, a cellulosic urban waste, municipal press cake, and pig manure for the pro-
duction of biochar. They studied extensively the physical and chemical properties
of biochar produced from these wastes for understanding potential use in agricul-
ture. It was found from their study that the physicochemical properties of biochars
depend on their composition (amount of lignin, cellulose, hemicellulose; nutrients)