**2.2 Energy crops**

*Biotechnological Applications of Biomass*

pollutant emissions.

environment.

**2. Types of biomass**

**2.1 Forestry biomass and residues**

in urban areas is growing although many cities still rely heavily on conventional energy sources based on fossil fuels. The use of the energy sources has stirred a heated debate on energy sustainability since they are associated with environmental pollution and the apparent climate change state [1]. In China for instance, the exponential growth in use of natural gas resulted to a 2–7% increase in carbon dioxide emissions correspondent to extensive air pollution in China [2]. Evidence showing that cities are the greatest environmental polluters and climate change contributors from the 70% carbon dioxide emissions out of the total possible, most of which is anthropogenic-based confirms the need for alternative, reliable, easily accessible and low-carbon emitting energy sources [5]. Zaharia et al. [4] agreed with these sentiments claiming that prosperity, population and non-renewable energy consumption in developing economies of Asia and Africa are attributable to the rise in

Of these proposed alternatives in the energy mix is biomass, which is organic matter that is used as energy directly for heating and combustion or indirectly as biofuels [6]. Biofuel examples include wood shavings, sawdust, firewood, fruit stones (avocados, olives and nutshells) wastewater, manure, paper waste and pellets. Biomass especially from wood is a promising domestic energy source according to Bildirici and Ozaksoy [7] who reported that 81% of African population depend on it for economic, household and cooking activities. The wide availability of biomass obtained from agricultural and industrial processes' by-products justifies it high preference. Additionally, its direct and indirect uses to produce energy make its suitable in developing regions of Africa. However, it is worth noting that direct use of biomass is not always feasible and in some cases require additional treatment (biologically or physically) to prevent the effects of conventional fuels [1]. This book chapter focuses on the various sources of biomass in Africa and assesses their potential in addition to having a candid discussion on the carbon neutrality of biomass. Three categories of biomass including forestry biomass, energy crops and wastes or residues will be discussed. The prospects of the chapter will help in drawing a roadmap to providing reliable energy for socio-economic growth in Africa while at the same time, taking precautionary measures to conserve the

Biomass, which is sourced from organic matter from the biosphere (animal or plant origin) and through transformation of wastes, is a promising source of energy. This renewable energy source can be classified into three: (1) forestry biomass, (2) energy crops and (3) biomass from wastes and residues. These three

Forests as terrestrial ecosystems store and generate biomass, which justifies their applicability as energy sources since time immemorial [8, 9]. This biomass form differs based on topography, stand structure, site and management systems. Irrespective of the variations, forest is a primordial energy source due to its uniformity and availability globally as well its carbon neutrality [10, 11]. Forest biomass is removed as harvests or in silvicultural activities. Forest biomass is classified into two categories: (1) energy plantations and (2) timber systems where energy is produced as forest residues. Energy plantations are distinguished from agricultural crops from the ability to enhance their biodiversity, their variability globally,

forms of biomass will be discussed in the following sections.

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Energy crops are wild and cultivated crops, which produce biomass for various purposes. They exist as woody, herbaceous, perennial, or annual and generate raw materials for gaseous or liquid biofuels in addition to solid biomass. A number of factors including maintenance of land productivity, improved soil fertility, use of crop rotation systems, climate change adaptation and crop characteristics influence the successful production of energy crops [19]. Energy crops are used for three main purposes: 1) biodiesel, 2) bioethanol and 3) electric and thermal production [20]. Some of the crops used to produce biodiesel include *Cynara cardunculus,* cotton, *Glycine max, Helianthus annuus* and *Brassica napus*. Energy crops used in bioethanol production include *Beta vulgaris*, *Zea mays* and *Sorghum bicolor*, wheat among other cereals. *Miscanthus giganteus*, *Eucalyptus globulus* and *Arundo donax* are used in electric and thermal production. According to Lynd et al. [21], energy crops occur in four categories: (1) cellulosic such as trees, grass and a variety of wastes, (2) oil rich such as palm oil, soy, rapeseed and sunflower, (3) sugar rich including sugar beet and sugarcane and (4) starch rich crops such as sorghum, wheat and maize. A number of conversion technologies transform the crops to energy. These technologies include biological processes such as fermentation, lignocellulose hydrolysis and anaerobic digestion as well as non-biological processes such as transesterification, pyrolysis, gasification and combustion. African countries such as Kenya, Zimbabwe, South Africa, Tanzania, Ghana and Ethiopia have embraced the use of these biomass crops as energy sources in addition to the use of forest biomass, residues and other forms of wastes [21].

### **2.3 Biomass from wastes**

Municipal solid waste commonly known as garbage comprises of leather and wood by-products, leaves, clippings from grass, food wastes, cardboard, paper and biogenic material from plants and animals. All these form biomass and can be transformed to energy for heating or steam for electricity generation. This has been done in developed countries such as the USA where in 2018, 14 billion kilowatt-hours of electricity from combusting 29.5 million tons of municipal solid waste was produced by 68 power plants [22]. More than 60% of the combustible waste consisted of biomass materials and accounted for the more than 50% of the generated power [22]. The remaining combustible weight was from non-biomass materials such as plastics. Landfill gas also made from biomass material is transformed to methane gas and used in energy production. In Africa, the use of municipal solid waste for energy production has high potential as Scarlat et al. [23] concluded in an evaluation of its potential especially in urban areas of the continent though it is done at small-scale levels.
