were well scrutinized (Matsakas et al. 2018; Abghari and
Chen 2017; Garlapati et al. 2016). Bioconversion processes
are typically performed in bioreactors that might be governed in a batch, semi-continuous, or continuous approach.
But definite bioreactor configurations might be chosen for
specific bioconversion applications. This technology could
be useful in the conversion of solid phase into the gas phase
along with liquid bioprocesses. For any feedstock, bioreactor
configuration, biocatalyst, and operating conditions should
be optimized concerning chemical composition and pH
range (Abghari and Chen 2017; Ginésy et al. 2017). The
bioconversion process is ecologically friendly and is an
alternative to both conventional chemical procedures and
petroleum processing processes. Such a process also
encourages the generation of a wide array of value-added
end materials through low-cost biocatalysts with moderate
reaction requirements.
2.2 Sources of Biowastes Generation
As mentioned above, “biowastes” refer to biodegradable
materials, including vegetable wastes, fruits, domestic
wastes, agriculture waste, animal and industrial wastes, etc.
However, the biodegradability of these materials is mostly
determined by the microbial strain and chemical structure of
the components. Several types of biowastes and their corresponding bioconversion methods are discussed as follows
(Fig. 4).
2.2.1 Fruits and Vegetable Wastes
As per the Food and Agriculture Organization (FAO) of the
USA, 790 million tonnes of fruits along with 950 million
tonnes of vegetables were produced in 2014. Both fruits and
vegetables are high energy and nutritious food items containing solvable carbohydrates, minerals, vitamins, good
fibers, and other bioactive components (Schieber 2017).
From farm to fork, fruit and vegetable wastes are mostly
produced from the following steps starting from cultivation,
processing, boxing, and shipping (Ji et al. 2017). Sometimes
these items are rejected from customers when they are
subjected to wounding, staining, thermal exposure, and
microbial attacks (tainted and unwanted surface growth).
This leads to heavy fiscal damage of about US$ 484 million
per annum because of the wastage of around 50 million
tonnes of fruits and vegetable waste (Panda et al. 2016). As
per the report obtained from FAO, in 2014, UK produced
about 5.5 million tonnes of potatoes from which about 13%
of the cultivated crops did not reach the consumer and were
wasted due to the “low-grade” standard at supermarkets. In
general, produced waste is managed through animal feeding,
dumping on land, burning, and composting. These dumping
methods induce serious ecological problems including
emissions of greenhouse and toxic gases (Ji et al. 2017;
Dessie et al. 2018). Such biomass must be used for
value-added applications to avoid such problems.
2.2.2 Agriculture Waste
Agricultural waste is an organic and biodegradable material
that possesses minerals, proteins, fibers, and vitamins. The
agricultural sector generates mostly lignocellulosic wastes
like straw (dry stalks of crops), molasses, spent grains,
bagasse, husk (wheat, rice, and maize), shells (groundnut,
walnut, and coconut), cotton stalks, and plant waste every
year around the world (Madurwar et al. 2013; Dai et al. 2018).
Lignocellulose wastes largely contain three main components
including lignin, cellulose, and hemicellulose (Madurwar
et al. 2013). As per 2013, FAO reports around 250 million
tonnes of plant wastes were produced from various crop
processing (Heredia-Guerrero et al. 2017). Typically, all these
agricultural wastes are either burned or rotten in the fields,
which cause serious air contamination (emissions of lethal
gases, for instance, CH 4 , N 2 O, and SO 2 , and soot, etc. into the
atmosphere) as well as high soil and water contamination.
However, agricultural biowaste is promising and resourceful
material for the generation of wide-range materials including
bioplastic and bioethanol using different portions of a plant
(Heredia-Guerrero et al. 2017; Krishnan et al. 2010; Chandel
et al. 2012). Some efforts are going on to properly utilize these
wastes. For example, China is utilizing straw for bioenergy
production. Zeng et al. observed that straw is the leading
(over 70%) source of bioenergy from biowaste in China
(Zeng et al. 2007).
Fig. 4 Classification of various sources of biowastes for bioconversion
processes
Bioconversion of Biowastes for Energy Applications
5
Chen 2017; Garlapati et al. 2016). Bioconversion processes
are typically performed in bioreactors that might be governed in a batch, semi-continuous, or continuous approach.
But definite bioreactor configurations might be chosen for
specific bioconversion applications. This technology could
be useful in the conversion of solid phase into the gas phase
along with liquid bioprocesses. For any feedstock, bioreactor
configuration, biocatalyst, and operating conditions should
be optimized concerning chemical composition and pH
range (Abghari and Chen 2017; Ginésy et al. 2017). The
bioconversion process is ecologically friendly and is an
alternative to both conventional chemical procedures and
petroleum processing processes. Such a process also
encourages the generation of a wide array of value-added
end materials through low-cost biocatalysts with moderate
reaction requirements.
2.2 Sources of Biowastes Generation
As mentioned above, “biowastes” refer to biodegradable
materials, including vegetable wastes, fruits, domestic
wastes, agriculture waste, animal and industrial wastes, etc.
However, the biodegradability of these materials is mostly
determined by the microbial strain and chemical structure of
the components. Several types of biowastes and their corresponding bioconversion methods are discussed as follows
(Fig. 4).
2.2.1 Fruits and Vegetable Wastes
As per the Food and Agriculture Organization (FAO) of the
USA, 790 million tonnes of fruits along with 950 million
tonnes of vegetables were produced in 2014. Both fruits and
vegetables are high energy and nutritious food items containing solvable carbohydrates, minerals, vitamins, good
fibers, and other bioactive components (Schieber 2017).
From farm to fork, fruit and vegetable wastes are mostly
produced from the following steps starting from cultivation,
processing, boxing, and shipping (Ji et al. 2017). Sometimes
these items are rejected from customers when they are
subjected to wounding, staining, thermal exposure, and
microbial attacks (tainted and unwanted surface growth).
This leads to heavy fiscal damage of about US$ 484 million
per annum because of the wastage of around 50 million
tonnes of fruits and vegetable waste (Panda et al. 2016). As
per the report obtained from FAO, in 2014, UK produced
about 5.5 million tonnes of potatoes from which about 13%
of the cultivated crops did not reach the consumer and were
wasted due to the “low-grade” standard at supermarkets. In
general, produced waste is managed through animal feeding,
dumping on land, burning, and composting. These dumping
methods induce serious ecological problems including
emissions of greenhouse and toxic gases (Ji et al. 2017;
Dessie et al. 2018). Such biomass must be used for
value-added applications to avoid such problems.
2.2.2 Agriculture Waste
Agricultural waste is an organic and biodegradable material
that possesses minerals, proteins, fibers, and vitamins. The
agricultural sector generates mostly lignocellulosic wastes
like straw (dry stalks of crops), molasses, spent grains,
bagasse, husk (wheat, rice, and maize), shells (groundnut,
walnut, and coconut), cotton stalks, and plant waste every
year around the world (Madurwar et al. 2013; Dai et al. 2018).
Lignocellulose wastes largely contain three main components
including lignin, cellulose, and hemicellulose (Madurwar
et al. 2013). As per 2013, FAO reports around 250 million
tonnes of plant wastes were produced from various crop
processing (Heredia-Guerrero et al. 2017). Typically, all these
agricultural wastes are either burned or rotten in the fields,
which cause serious air contamination (emissions of lethal
gases, for instance, CH 4 , N 2 O, and SO 2 , and soot, etc. into the
atmosphere) as well as high soil and water contamination.
However, agricultural biowaste is promising and resourceful
material for the generation of wide-range materials including
bioplastic and bioethanol using different portions of a plant
(Heredia-Guerrero et al. 2017; Krishnan et al. 2010; Chandel
et al. 2012). Some efforts are going on to properly utilize these
wastes. For example, China is utilizing straw for bioenergy
production. Zeng et al. observed that straw is the leading
(over 70%) source of bioenergy from biowaste in China
(Zeng et al. 2007).
Fig. 4 Classification of various sources of biowastes for bioconversion
processes
Bioconversion of Biowastes for Energy Applications
5