Renewable and Sustainable Energy Reviews 76 (2017) 941–949
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Renewable and Sustainable Energy Reviews
journal homepage: www.elsevier.com/locate/rser
Poultry litter as biomass energy: A review and future perspectives
a,⁎
a
MARK
b
Felipe Santos Dalólio , Jadir Nogueira da Silva , Angélica Cássia Carneiro de Oliveira , Ilda de
Fátima Ferreira Tinôcoa, Rúben Christiam Barbosaa, Michael de Oliveira Resendea, Luiz
Fernando Teixeira Albinoc, Suani Teixeira Coelhod
a
Departament of Agricultural Enegineering, Universidade Federal de Viçosa, Campus Viçosa, Avenue Peter Henry Rolfs s/n, Viçosa, Minas Gerais CEP
36570-000, Brazil
b
Departament of Forest Enegineering, Universidade Federal de Viçosa, Campus Viçosa, Avenue Peter Henry Rolfs s/n, Viçosa, Minas Gerais CEP 36570-000,
Brazil
c
Departament of Animal Science, Universidade Federal de Viçosa, Campus Viçosa, Avenue Peter Henry Rolfs s/n, Viçosa, Minas Gerais CEP 36570-000,
Brazil
d
Centro Nacional de Referência em Biomassa (CENBIO), Universidade de São Paulo, Universitary city, Avenue Prof. Luciano Gualberto, 1289, São Paulo
CEP 05508-010, Brazil
A R T I C L E I N F O
A BS T RAC T
Keywords:
Aviculture
Combustion
Wastes
Gasification
Pyrolysis
Sustainability
Poultry litter is characterized as a heterogeneous compound produced after a poultry production cycle, being the
sum of the material used as bedding in association with the animal waste, dead skin, feed scraps, water, feathers
and the resulting microbiota. The expansion of poultry production around the world has resulted in elevated
generation of this residue. Over the years its use has been restricted to organic fertilizer or simply as a waste to
be eliminated and disposed of in the environment. However, this mechanism has caused environmental and
social damages due to its indiscriminate use. Because of the energetic and biological properties of poultry litter,
its sustainable use as energy can be obtained via thermochemical processes such as anaerobic digestion and
through combustion, gasification, pyrolysis or power co-generation systems, in which there is a combination of
one or more processes. As a result, there is the potential for generating heat, electricity, fuel gas and biochar
with low emission of pollutants. However, it is emphasized that there is no standard with regards to its
composition and the source material type, where efforts are more focused on the contents of moisture and
inorganic compounds. Therefore, processes that seek to use poultry litter as fuel biomass should be wellcontrolled and efficient for successful energy generation. In this sense, the objective of this study is to analyze
the characteristics of poultry litter as fuel, discuss the main thermochemical processes for its energetic
conversion and propose measures to improve its performance as a sustainable biomass.
1. Introduction
The production of broiler chickens has been significantly growing
throughout the world, and therefore the high generation of waste
becomes a concern for the agricultural sector that increasingly seeks
sustainable alternatives for the use of generated wastes. According to
Abelha [1], poultry waste may be used for sustainable renewable energy
generation, and methods should be explored due to its potential as a
fuel and not simply as a waste to be eliminated [2], since its
heterogeneous character may cause problems when indiscriminately
disposed of in the environment. In this sense, it is necessary to seek
measures for proper use of poultry litter for energetic purposes.
The use of poultry litter as a sustainable fuel has been studied for
some years for use in thermochemical conversions such as direct
⁎
burning, or by means of gasification and pyrolysis [3,4]. It has been
observed that the gasification and pyrolysis processes of poultry litter
present high quality results for the production of fuel gas, reducing
emissions and generation of biochar [5–7].
Given the above, the present review sought to analyze the intrinsic
characteristics of poultry litter as a fuel, as well as discuss the main
thermochemical processes for its energetic conversion and propose
measures to improve its performance as a sustainable biomass.
2. Waste generation by broiler poultry
The measured data available in literature in relation to the quantity
of poultry litter generated per bird in a 42 day production cycle is quite
variable, ranging from 1.5 to 5.7/kg of litter/bird [2,8]. It is common to
Corresponding author.
E-mail address: felipesantos181@hotmail.com (F. Santos Dalólio).
http://dx.doi.org/10.1016/j.rser.2017.03.104
Received 30 September 2016; Received in revised form 27 November 2016; Accepted 23 March 2017
1364-0321/ © 2017 Elsevier Ltd. All rights reserved.
Renewable and Sustainable Energy Reviews 76 (2017) 941–949
F. Santos Dalólio et al.
contamination of the water table has been reported due to excessive use
of poultry litter as fertilizer [25]. Oviedo-Rondón [26] affirmed that in
some regions of the United States, such as Minnesota and North
Carolina, saturation of the soil has also occurred due to intense
application of litter, and in order to avoid this problem its application
for generating electricity should be considered.
It should also be stated that after a production cycle the litter may
contain many pathogens that survive up to 11 weeks outside the
digestive system of the birds [27]. Additionally, antibiotic residues used
as a growth promoters or for the treatment of diseases may be detected,
which are not fully absorbed by the birds and up to 75% may be
released to the environment [28]. According to Hahn [29], the main
microorganisms present in poultry litter are Escherichia coli,
Salmonella and oocysts of Eimeria. Therefore, the use of poultry litter
as organic fertilizer, without appropriate treatment, may cause adverse
effects to the ecosystem since the antibiotics used in poultry production
have been detected in soil, water, plants and sediments [30].
Although poultry litter has advantages with regards to its use as a
fertilizer, it is currently verified that its use causes environmental and
social damage due to indiscriminant application [7]. In this sense, it is
necessary to seek new rational alternatives for the use of poultry litter
that result in less impact to the environment with appropriate
treatment to eliminate undesirable compounds and pathogens.
Among the available alternatives, the use of poultry litter as biomass
energy for generation of heat and electricity is gaining prominence
[4,7,31,32].
use poultry litter in more than one production cycle for chickens. In
Brazil, the average is 6 cycles with the same bedding. And this helps to
reduce the volume of generated bed. However, the volume reduction
fact not completely minimizes high production chickens generate high
amount of waste.
Brazil is the second largest world producer of broiler chickens and it
is estimated that the annual volume of litter generated is around 8–10
million tons/year. This calculation is based on the number of chickens
slaughtered each year multiplied by the litter volume generated per
bird. According to Santos [9], for Brazilian conditions each bird over 42
days produces an average of 1.75 kg of litter, based on natural matter,
assuming that the litter has an average moisture content of 20%. Thus,
independent of the amount of poultry litter generated, it is noted that
the total volume of this residue is high due to elevated productivity, and
constitutes a growing concern regarding its disposal. Therefore, it is
necessary to analyze this material with regards to its chemical
composition as a fuel biomass and its current use as an organic
fertilizer.
3. Poultry litter: use as organic fertilizer
After a poultry production cycle, in addition to wastes there is also
flaked skin from the birds, waste feed, water, feathers and the
microbiota resulting from this heterogeneous mix [10]. Moreover, it
also contains antimicrobial and antibiotic residues, which are used as
growth promoters and for treatment of infections, endocrine disruptors
such as chicken metabolic products, and residues of pesticides and
herbicides used in cultivation of the grains used for feed manufacture
[11,12].
At present, the main destination of poultry litter is its use as organic
fertilizer and/or manufacture of organo-mineral fertilizers, due to its
contents of nitrogen, phosphorus and potassium. The litter is presented
as a potential organic fertilizer, because in addition to the concentration of nutrients, it permits the inclusion of organic matter to the soil,
improving both the physical and chemical attributes [13].
The physico-chemical composition of poultry litter depends on
certain parameters such as the type of material from which the litter is
produced, for how many consecutive flocks it was used and the
management practices employed during production of the birds [10].
In order for a material to be used as litter it must be of medium size,
have good absorption capacity without hardening, easily release
trapped moisture, have low thermal conductivity with capacity to
withstanding high densities, and most importantly be of low cost.
The main materials used as poultry litter are wood shavings, coffee
hulls, peanut hulls, rice hulls, dry grass, chopped corn cobs and others
[14–16]. According to Toghyani [17], the type of material used as litter
does not affect the performance parameters of poultry, considering that
they are handled properly in the installations. However, Vieira [18]
observed a reduction in the sanitary quality of coffee hull poultry litter
in four reuses. As a result, increased incidence of lesions to the carcass
was observed due to increased nitrogen concentration in the bed.
Despite the concentration of beneficial nutrients, the massive use of
poultry litter as organic fertilizer can result in eutrophication processes
in soil and water bodies, the spread of pathogens, production of
phytotoxic substances, air pollution and greenhouse gas emissions
[3,19]. One of the main concerns regarding the disposal of litter in the
environment, when applied as fertilizer, has been the presence of
endocrine disruptors, especially 17β-estradiol [11]. Its effect is still
unknown, however it is believed to cause sexual reversal in fish when
poultry manure is applied in excess in the soil and subsequently
leached to water bodies [20,21].
Another barrier to the use of poultry manure as organic fertilizer is
the continuous application to soil to improve the production rates of
agricultural crops. This can result in high toxicity to animals and plants
along with depreciation of the product, however this is only perceived
in the medium and long term [22–24]. In the Brazilian state of Paraná,
4. Poultry litter: biomass energy
Given the high volume generated by broiler poultry and due to
shortage of energy sources and the high price of conventional sources,
the use of poultry litter as biomass energy is becoming attractive
[3,4,6,7,33] and therefore it may become both technically and economically feasible. Available literature on the use of poultry litter as
biomass energy in industrial production units is still incipient.
Recent studies indicate the efficiency of heat and energy production
from poultry litter in locations near the waste-generating units [4,33].
This is because the cost related to transport is a major factor to be
addressed when seeking efficient power generation from any type of
biomass.
For utilization of alternative biomasses some factors are important,
where the main characteristics are: moisture content, energy density,
calorific value, the amount of generated volatile material generated
during combustion, the volume of ash at the end of the process, the
fixed carbon content, the chemical analysis and the elemental content
[34,35].
The moisture content is one of the main indices of non-inherent
quality of the evaluated residue, since elevated moisture content may
result in more energy consumed for drying the biomass prior to
combustion processes. It also influences the initial ignition capability.
This decreases the process efficiency and impairs the energy and
thermodynamic equilibrium in the final calculation. Furthermore, the
high moisture content leads to incomplete combustion and consequent
release of carbon monoxide to the environment [36]. In general, for the
efficient generation of heat and electricity from poultry litter, it is
recommended that the moisture content does not exceed 25% [1].
The calorific value of any biomass can be defined as the amount of
energy released in the form of heat during complete combustion of the
fuel mass unit, which can be measured in kJ/kg [37]. Energy density is
another important parameter, since in terms of transport and storage it
becomes crucial, corresponding to the average mass of a solid for a
given volume.
The volatiles content is the amount of material that will volatilize at
high temperatures and indicates the reactivity of the fuel. In general,
for plant biomass the volatile content varies from 65% to 83% [37],
whereas in biomass of animal origin the value is more heterogeneous
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F. Santos Dalólio et al.
and may vary from 40% to 75%, due to lack of standardization. Ashes
result from burning products which are unreactive in the process and
represent about 2% of plant biomass and up to 45% of animal biomass.
The fixed carbon content directly influences the temperature to be
employed in the thermochemical processes, such as pyrolysis for
example. In general, as the fixed carbon content of the biomass
increases, greater is the temperature for ignition and subsequent
combustion [38].
Organic animal residues have very low fixed carbon content,
because this variable is obtained subtracting the ash and volatile
material from the total mass to be burned [39]. The immediate
chemical composition corresponds to the sum of moisture, ash, volatile
matter and fixed carbon in relation to total mass of a fuel. This
relationship indicates not only the amount of water present in the
biomass, but also the possible fuel behavior and its effectiveness in
energy processes [40]. Therefore, it is a relevant parameter for animal
residues.
The chemical elemental composition indicates the amount of each
compound present in the biomass. However, it is governed by the levels
of: carbon, hydrogen, nitrogen, sulfur and oxygen. These directly
influence the thermochemical processes, where oxygen, nitrogen and
sulfur cause damages. Excess sulfur present in the biomass is released
into the atmosphere in reaction with oxygen to form SO2 and becomes
a significant environmental problem. The concentrations of hydrogen
and carbon contribute positively, where the higher their content the
more efficient is the release of energy. Cortez [37] reported that the
chemical elemental composition is the basis for analysis of combustion
processes and is useful for the calculation of volumes of air, gases and
enthalpy, and is essential for determining the calorific value.
Considering the main aspects that influence and determine the
quality of a biomass to be used as fuel energy, it is necessary to evaluate
and analyze the poultry litter with regards to its physico-chemical
composition.
Table 2
The main chemical composition parameters of poultry litter, of wood savings, to be used
for energy purposes.
Components
Proximate (%)
Fixed carbon
Volatile
Moisture
Ash
Elemental (%)
C
H
O
N
S
Cl
Ash
Moisture
Poultry litter compared to the other wastes from animals produced
in confinement systems presents some advantages due to inclusion of
the material used as litter which raises the carbon concentrations [41].
Table 1 shows the chemical composition data of animal wastes with
regards to their potential for use as fuel for thermochemical processes.
In comparison with the other waste types, poultry litter used in
thermochemical processes requires lower temperatures due to the
elevated concentration of volatiles, higher carbon and hydrogen conTable 1
Mean chemical composition values of some animal wastes that can be used for energetic
purposes.
Cattle
manurea
Horse
manureb
Pig manurec
Hen
manured
Poultry
littere
Volatiles
Fixed carbon
Ash
Moisture
Cellulose
Hemicellulose
Lignin
C
H
N
O
S
53.1
4.6
42.3
24.6
32.7
24.5
42.8
21.9
3.6
2.3
20.8
1.1
–
–
10.9
19.0
37.8
32.4
19.6
–
–
–
–
–
73.0
3.4
23.6
–
16.6
–
1.6
12.3
1.7
0.9
–
0.1
–
–
10.6
39.7
–
–
–
24.8
3.8
7.3
17.0
3.0
48.8
–
34.3
19.3
–
–
–
27.8
5.7
4.3
–
1.1
a
b
c
d
e
[47]
[31]
[1]
[48]
[49]
[50]
[51]
9.80
47.30
27.40
15.70
14.00
62.20
25.50
23.90
–
–
–
–
1.70
38.90
43.00
16.40
8.11
54.72
10.59
26.58
13.06
43.48
9.29
34.28
10.20
50.30
8.20
28.80
–
53.96
10.47
–
27.22
3.72
23.10
2.69
0.33
0.71
15.70
27.40
35.60
4.60
29.80
5.30
0.90
–
23.90
–
34.70
5.20
24.09
5.60
0.13
0.35
–
–
28.17
3.64
34.43
3.78
0.55
0.63
–
–
29.09
5.11
–
3.44
0.80
–
26.58
10.59
37.78
4.19
15.64
3.76
0.74
0.80
37.79
–
24.84
1.90
33.76
2.50
2.50
2.50
28.80
8.20
27.82
5.08
–
4.25
1.14
–
39.18
–
tents, low sulfur concentration, and reduced moisture. These characteristics make poultry litter superior in relation to other animal wastes
and regarding potential to be used in power generation processes such
as gasification and pyrolysis.
It should be noted that the chemical composition of the various
animal wastes is variable considering that many factors affect its
composition, namely: diet and age, race, climate conditions, production
level and others. In the case of poultry litter, highlighted are other
factors such as litter material used to serve as bedding for the birds, the
use of acclimatization in aviaries, such as ventilation and exhaustion,
the number of reuses, management during production and management of wastes on the property. Table 2 presents some data on the
composition of poultry litter, with respect to its characteristics as a fuel.
Poultry litter presents high reactivity and can be used as fuel
biomass because it is rich in volatile material [4]. Furthermore, from
Table 2 it can be observed that the poultry litter has a low amount of
fixed carbon, therefore combustion in the solid phase may become
insignificant. This occurs due to high devolatilization of the compounds
in this phase, requiring lower temperatures for the thermal processes.
However, moisture of the litter is the most important parameter and
must always be correlated with the content of volatile material in order
to establish the optimum firing temperatures. Based on this, Abelha [1]
identified that at a humidity of 11% the ignition temperature for an
adequate thermal process would be 580 °C for 2 s, while for in natura
litter with 20% humidity, this value rose to 620 °C for 8 s. This is
important since it indicates greater energy consumption to release the
energy content of poultry litter, meaning higher costs, more sophisticated equipment and loss in the energy balance.
4.1. Composition of the poultry litter and other animal wastes
Parameters (%)
[46]
4.2. Atmospheric emissions and practical implications of using
poultry litter as biomass
One of the main factors to be evaluated when seeking the use of
alternative biomass for energy production is the emission of pollutants
to the environment that may occur during thermal processes, or even
thermochemical processes [41]. With respect to the non-conventional
organic residues, the major pollutants that can be generated and cause
negative impact to the environment and to the biomass transformation
process is the presence of chlorides, NOx, SOx, CO2 and excess CO
[52], in addition to other compounds such as dioxins and furans which
are also harmful [53,54].
Jia & Anthony [55] evaluated the atmospheric emissions released
by burning a mixture of 40% chicken manure and 60% coal compared
to the burning 100% coal and observed environmental viability of
burning the poultry litter. According to these authors, although the
concentrations of pollutants are higher for burning the mixture with
poultry litter, they are within the norms stipulated by the laws of
[42].
[43].
[44].
[45].
[4].
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Renewable and Sustainable Energy Reviews 76 (2017) 941–949
F. Santos Dalólio et al.
as well as the potential for their addition to silage for animal feed or for
enrichment of other fertilizers [4]. In practical studies, a positive effect
has been observed when using ash from the combustion of poultry
litter as an organic fertilizer in wheat planting, with potential to be used
in the production of other crops [61,62]. Moreover, ashes may also be
used as a source of phosphorus and calcium in poultry feeds [63].
Based on the material used as litter, ash resulting from thermal
processes will have a different composition, for example if derived from
straw it will have a higher potassium content (4–6%), while if from
wood shavings the concentration is lower (1.5%). Therefore, it can be
viably applied as a fertilizer in its natural form, however it would
ideally be applied as granules [60]. It should be noted that granulation
generates additional costs to the producer, so an economic evaluation
is necessary.
Canada, where the research was conducted.
The presence of sulfur in the fuel causes it to volatilize and
condense on the cooler surfaces of the combustor, so that there is
possibility of agglomeration and corrosion of the equipment [56]. As a
result, there is an increase in particle inertia and other undesired
chemical reactions, such as increased SOx emissions [57].
According to the data presented in Table 2, it can be observed that
the poultry litter has low amounts of sulfur. Loo & Koppejan [58]
stated that 90% of sulfur present in poultry litter may be fixed in the
ashes and this efficiency depends on the calcium concentration. This is
because calcium present in poultry litter, resulting from the addition of
lime in the treatment and reuse processes, increases the sequestration
of sulfur with the formation of oxides in the ash. With complexation of
S to the Ca there is greater stability of oxides in the ash, resulting in
improved capacity and potential of this material to be used as organic
fertilizer and as a correction agent for agricultural soils deficient in
these two elements.
However, the gradual increase in ash production at the end of the
thermal energy conversion process, as poultry litter is added as fuel,
may require that materials with higher carbon content are added to
improve the combustion efficiency and reduce the emission of pollutants. This can be explained by the higher amount of sodium and
potassium oxides contained in poultry litter that may be deposited on
the furnace walls and precipitate in cold areas, affecting the combustion process [59]. Moreover, there are increased chances of corrosion of
the internal walls of the combustors, reducing their useful life.
Therefore, it is essential to understand the composition of the litter
together with its efficiency for power generation.
5. Use of poultry litter as an energy source
Sordi [25] evaluated poultry litter of pine wood as an energy source
in the western region of the Brazilian state of Paraná and found that the
theoretical energy potential was 142,500 kJ/s, with potential power
generation up to 50,700 kW. We conducted a study at the Federal
University of Viçosa, part of the Zona da Mata mesoregion in Minas
Gerais, Brazil, to evaluate poultry litter of coffee hulls as an energy
source considering a hypothetical scheme for generation of electricity
via a steam cycle, and found that the generation potential is 8800 kW
from a regional production of 6552 t/month, assuming a thermodynamic efficiency of 30%. However, the efficiency may be increased to
75% by utilizing the turbine exhaust steam in the co-generation
process. The poultry slaughter and meat processing industry itself
requires power and steam for industrial processes, and could use the
energy produced from poultry litter, closing the loop and making the
activity sustainable.
Although literature regarding the use of poultry litter as a fuel is still
very incipient, its viability as biomass may be verified. This considers
that there is knowledge of its composition, purpose of use, the concern
of not generating pollutants, harmful emissions and unwanted ash
resulting from poorly sized processes. Energy conversion of poultry
litter may occur via thermochemical transformations such as direct
combustion, gasification and pyrolysis.
4.3. Residual ash from combustion of the poultry litter: composition
and possibilities of use
Although poultry litter has a considerable amount of residual ash
after thermal processes, it is made more stable and sterile because it
has no pathogenic microorganisms, is easier to handle and transport,
and is more marketable compared to conventional poultry litter [3].
Front-Palma [60] and Lynch [4] identified the composition of the ash
derived from co-combustion processes of poultry litter of wood
shavings with coal in gasification systems. This data is presented in
Table 3.
From Table 3 it is possible to identify the high levels of potassium,
calcium and phosphorus minerals and the presence of micronutrients
essential to the soil and plants. It is highlighted that the mineral
nutrients present in the ashes have higher availability and stability than
those provided from in natura poultry litter. This fact results in a
reduced environmental impact and greater efficiency in organic
fertilization.
There are several ways of applying the ashes from poultry litter
combustion to soils with low macro and micronutrient concentrations,
5.1. Combustion of poultry litter: theoretical and practical aspects
The use of the energy contained in biomass by combustion is a
rudimentary form and the most used due to its ease of use and
suitability. Although very practical and sometimes convenient, the
direct combustion process can become very inefficient and uneconomical because it depends on several factors such as fuel type, moisture
content, calorific value, energy density, and includes difficulties of
transport and storage [64].
The combustion of poultry litter seeks to produce heat and the
possibility of providing this heat for other purposes. Highlighted are
boilers to generate steam and hot air for industrial processes, power
generation or for direct supply of heat in furnaces, for example heating
of animal installations and grain drying [3]. According to Dagnall [65],
the heating value of poultry litter ranges from 9000 to 13,500 kJ/kg,
depending on the material and moisture content. Sordi [25] affirmed
that for poultry litter composed of wood shavings with 25% moisture
content, the calorific value is 11,600 kJ/kg. Poultry litter has a
relatively good calorific value compared to other animal wastes, but
has a low ash melting point due to the concentration of sodium and
potassium in its composition [66]. This may result in formation of
undesirable liquids, fouling the equipment used for burning and
efficiency losses in the process [39].
Due to the amounts of nitrogen, volatile material and sulfur in the
composition of poultry litter, it is necessary to use an ideal mixture of
air and fuel within the combustion chamber to promote efficiency and
Table 3
Composition of the ash resulting from co-combustion of poultry litter with coal.
Elements (mg/kg)
[60]
[4]
Boron
Calcium
Potassium
Phosphorus
Magnesium
Selenium
Sodium
Cobalt
Copper
Iron
Manganese
Molybdenum
Zinc
–
185,000
163,000
202,000
42,000
–
3600
–
–
2100
–
–
–
270
160,000
170,000
110,000
39,000
12
2000
8.8
590
6500
4200
79
3800
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F. Santos Dalólio et al.
process and the quality of gases and secondary emissions is vital for
environmental feasibility of any project that seeks to use poultry litter
for the production of heat and energy. In this sense, the need for
existing mechanisms is clear to improve and enhance the use of poultry
litter as a sustainable fuel.
The use of other processes for conversion of poultry litter into
energy including gasification and pyrolysis, or a combined cycle of
both, enables increased energy efficiency [7]. In addition, the search for
management factors such as proper feeding of the birds, management
of the environment and efficient management of the litter on which the
birds are housed are important factors to improve the quality and
composition of this waste, making poultry production more productive
and economically viable, because it is a relatively low gross profit
activity.
minimize environmental impacts.
The moisture content of in natura poultry litter is the main obstacle
to its use in direct combustion. Dávalos [31] evaluated the direct
combustion of poultry litter in natura, wet (70.4% moisture) and dried
to less than 10%. These authors found that only the litter with 9%
moisture can be burned directly without adding extra fuel and in the
wet and in natura samples there was incomplete combustion with the
formation of excess carbon monoxide and higher pollutant emissions.
This fact indicates that drying of the material must be accounted for in
the energy balance for its use as fuel in order to identify its economic
and financial viability.
In the exploitation of poultry litter to generate energy, the emission
of harmful pollutants to the environment and effects on health of the
surrounding population can be a barrier to its use, due to the fact that
there is no standard regarding its composition. This generates concern
regarding air emissions generated from combustion of poultry litter,
especially the possibility for formation of NOx, SOx, HCl and dioxins
[2,6].
The nitrogen present in poultry litter is in the form of ammonium
unlike other types of biomass used in controlled burning, where
nitrogen is in the form of complex organic nitrogen. Ammonium
present in poultry litter during combustion is quickly converted to
ammonia by rapid volatilization. Furthermore, at elevated temperatures of around 800 °C, ammonia rapidly converts NOx to N2 [67].
Billen [6] identified differences in atmospheric emissions of nitrogen
from poultry litter according to its use, since when applying poultry
litter as fertilizer the emission was 25 mg/kg litter, while in combustion
or fluidized bed gasification it was 0.0017 mg/kg of litter. This
indicates less environmental pollution when using the litter as fuel
when compared to its use as fertilizer. Table 4 presents some results
concerning atmospheric emissions resulting from the burning of
poultry litter and coal.
Although the presence of dioxins and furans was detected in
atmospheric emissions from burning of poultry litter, Billen [6] noted
that these values are below the limits recommended by the European
Union. It should be noted that this legislation is the most demanding
with respect to emission of these elements. Thus, it is emphasized that
if thermal control processes, operation and the respective air intakes
are appropriately considered, emissions from burning of poultry litter
will be satisfactory.
Zhu and Lee [68] evaluated the co-combustion of poultry litter
mixed with sawdust and using natural gas as the ignition fuel,
observing that it is operationally viability to burn poultry litter with
reduced emissions of CO and NOx. However, they stressed that further
studies are needed in order to identify the emissions generated from
other thermal processes.
Optimization mechanisms of existing thermochemical processes
such as the use of technological tools are essential for improving energy
efficiency. According to Huang [5], computer modeling for total control
of feed to the combustor, the air vents, the heat generated in the
6. Gasification of poultry litter
Gasification is the thermochemical process of converting a solid or
liquid raw material into a gas with fuel characteristics, by its partial
oxidation at intermediate temperatures. The thermochemical reactions
occur at temperatures above those recommended in fast pyrolysis
processes and below those recommended in combustion processes
[37].
In the gasification process restricted amounts of oxygen are
supplied in its pure form or simply as atmospheric air, depending on
the final use of the gas. The material may also be gasified in the
presence of controlled amounts of superheated steam. This steam is the
gasification agent needed to produce a gas mixture known as synthesis
gas, rich in hydrogen and carbon monoxide [69]. In general, the
produced synthesis gas has many practical applications, from combustion in internal combustion engines and gas turbines for the generation
of mechanical and electric energy, as well as direct heat generation
[70].
The gasification of poultry litter can be successfully used for
production of fuel gas [3]. Gasification of poultry litter using a fluidized
bed combustor, mixed with other wastes such as peat and tailings from
mineral and charcoal production, presents technical and environmental viability [55,71,72]. Quiroga [73] stated that the biomass sources
most feasible to be mixed with poultry litter, to favor the energetic
aspects of gasification, are forest-based residues and those from
agricultural production. The objective would be to increase the fixed
carbon content and reduce the excessive formation of volatile components early in the process. However, to reduce emissions of SOx, NOx
and CO it is recommended to use computational modeling to optimize
the combustion and production of high quality fuel gas [7,71].
The existing results in literature that used the poultry litter, alone or
mixed with other biomass for gasification, were unanimous in affirming
that the best system to be used is the fluidized bed gasifier [4]. This is
because the fluidized bed gasifier allows for use of a wide range of solid
fuels, in addition to being a system with higher production capacity
compared to the others. It can produce, if well sized and managed, up
to five times more than fixed bed gasifiers [74].
The fluidization process promotes intimate contact between the
particles and gases, causing intense circulation and mixing of the
particles. In gasification of poultry litter a sand bed can be used to
increase contact between the particles and decrease the production of
ash [3], resulting in high gas-solid reaction rates and a uniform
temperature throughout the entire bed.
The main advantages of fluidized bed gasifiers are their flexibility
with regards to the material in the feed, ease in maintaining temperature control below the melting point of ash, and the ability to operate
with friable materials and those of fine particle sizes [70]. The
disadvantages that this type of reactor include the limited operational
temperatures and the possibility of tar production due to low operating
temperatures (700–900 °C), with a risk of incomplete biomass combustion [75]. However, studies with gasification in fluidized beds with
Table 4
Atmospheric emissions from the combustion of poultry litter and coal.
Elements
Unit
Poultry litter
Coal
CO2
CO
NOx
NH3
SO2
HCl
Hg
Cd+Tl (radioactive)
Heavy metals
Dioxins and furans
Kg
Kg
Kg
g
g
g
Mg
Mg
Mg
Ng
0.00
0.05
0.22
17.00
20.00
4.00
< 4.00a
< 9.00a
< 65.00a
< 44.00a
626.00
0.15
1.10
27.00
830.00
8.00
12.00
0.90
262.00
53.00
a
Below the detection limits, overestimated value. Within the current standards of the
European Union - Adapted from [6].
945
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F. Santos Dalólio et al.
density per area and the optimal acclimatization of production
installations, with respect to bioclimatic indices of temperature and
humidity, are important management measures [83] since they avoid
excessive water consumption, food waste on the litter and proper
transit of birds along the installation to avoid water and waste
accumulation zones.
In preparing of feeds, an appropriate nitrogen and digestible amino
acid balance can be adopted using the ideal protein concept, decreasing
nitrogen excretion in the litter [84]. It can promote digestibility of the
feeds with the supply of more digestible ingredients that allow better
assimilation of nutrients by the birds. Also, exogenous enzymes can be
used such as phytase, protease and enzyme complexes, increasing the
utilization of phytate and proteins, and reducing the excretion of
nitrogen and phosphorus [85]. A proper electrolyte balance of the
feeds can also be adopted to allow proper water consumption and
reduce its excretion in the litter, maintaining it drier. The combination
of these nutritional mechanisms can increase the quality of the litter to
be used as biomass fuel and enable better performance of the chickens,
improving the sustainability of poultry production.
poultry litter observed no increased production of tar, NOx, SOx and
CO [5–7].
7. Pyrolysis of poultry litter
Pyrolysis may be defined as the thermal degradation of organic
material in the partial or total absence of an oxidizing agent, or even in
an environment with an oxygen concentration capable of preventing
intensive gasification of organic material [76]. It can be split between
slow and fast pyrolysis, where that which modifies each process are the
heating rates during the biomass decay time and the temperatures
used.
Fast pyrolysis takes place at elevated temperatures, around 900 °C,
producing fuel gas and small amounts of charcoal, about 10%. Slow
pyrolysis usually occurs within the temperature range of 300–450 °C,
until beginning the gasification system with the aim of producing
charcoal, bio-oil and synthesis gas [77]. In this process there is greater
coal production, with the higher concentration of carbon.
Slow pyrolysis of agricultural residues is commonly used to produce
biochar, bio-oil and syngas as co-products, which may be reinserted in
industrial thermochemical processes. In this technology, organic waste
is heated in batch reactors similar to coal furnaces or in continuous
flow beds, in total or partial absence of air. Typical yields of coal, biooil, and synthesis gas from wood waste are 30%, 28% and 42% of the
raw biomass material, respectively [78]. However, the biochar yield
and fuel characteristics of syngas vary according to the heat flux,
pyrolysis temperature, processing time, density and particle size [79].
Thus, it can be inferred that biomass which is homogeneous and has a
standard chemical composition generated higher and more defined
yields in relation to heterogeneous biomass.
Cantrell [80] found that chicken manure has a higher efficiency to
be used as substrate for the production of biochar than synthesis gas.
Song and Guo [32] evaluated the viability of slow pyrolysis of poultry
litter at different temperatures (300, 350, 400, 450, 550 and 600 °C),
and found that the temperature of 500 °C is most recommended to
generate bio-coal quality with yields of up to 60.2%, with a high
concentration of nutrients (N, P, K, Ca, Mg and S) to be used in organic
fertilizer.
The biomass composition modifies the properties and proportion of
compounds produced in pyrolysis. According Mante and Agblevor [81],
pyrolysis at 450 °C of a mixture of different proportions of poultry litter
in conjunction with wood chips produces different compounds. The
authors concluded that as the addition of wood was increased, the biooil yield also increased while the proportion of biochar decreased. It
was further found that bio-oil produced only with poultry litter has a
high energy content, low density, low viscosity and satisfactory pH
values. Ma and Agblevor [82] studied the fast pyrolysis of poultry litter
(450 °C) with the objective of producing bio-oil, and identified that the
bio-oil composition was 70.48% C, 8.78% H, 7.18% N, 13.56% S and
0% S. It was also identified that different fractions of oil were extracted
(hexane, toluene, methanol and chloroform) with a high average bio-oil
viscosity, indicating this raw material may potentially be used for
manufacturing bio-lubricants on an industrial scale.
8.2. Management of wastes and preprocessing of in-natura poultry
litter
Management of wastes should avoid improper disposal of poultry
litter after a productive cycle and favor that the litter does not absorb
moisture and does not eliminate or generate particulate pollutants to
the environment. If possible drying is recommended to remove excess
residual moisture in addition to processes that facilitate volatilization
of ammonia, such as composting. This will decrease the nitrogen
content which in turn negatively affects the thermal processes. Another
desirable process is standardization of the waste particle size which will
influence the thermochemical transformation.
8.3. Preprocessing of the poultry litter to improve the fuel properties
Regarding the preprocessing of unconventional biomasses, such as
poultry litter, some measures may be adopted such as compaction and
torrefaction of biomass to improve the fuel parameters [86,87].
8.3.1. Compaction
The compaction of poultry litter is recommended since this material
has a low density of around 500 kg/m3 [88]. The advantages of
compaction processes are numerous, especially the increased density
of the material, standardized dimensions of the biomass, process
automation, improved combustion efficiency, reduced moisture content and the possibility of storage and bulk transport.
The compacted material is about 5–6 times more energy density
than the source material, which allows for subsequent mechanization
of the process due to its homogeneity [89]. Nandi [90] indicated that
compaction of poultry litter reduces the emission of particulates and
pathogens during handling and transportation, and is also a suitable
form of treatment. However, the energy used in poultry litter compaction processes can make it a costly alternative if not performed
efficiently [91].
Sultana and Kumar [92] evaluated a future scenario with use of
poultry litter pellets, and observed low production costs, lower CH4
emission and higher gross mass content compared to wood pellets.
However, they released more NOX and SOX, showed lower durability
and low consumer acceptance, thus making it more cost effective to use
wood pellets for residential use. Still, the poultry litter pellets possessed
advantages from economic and environmental points of view, indicating possibilities for greater diffusion of their use in the future.
8. Future perspectives on the energetic use of poultry litter
8.1. Factors associated with production management and production
of feeds
Poultry litter has characteristics that allow for it to be used as
biomass fuel, however for efficient use it is recommended that it
present reduced contents of: moisture, nitrogen, sulfur, phosphorus,
sodium and potassium. These levels can be controlled by management
mechanisms on the farm which include the proper formulation of
feeds, management in poultry houses and waste management.
Proper management of the birds so as to avoid excess animal
8.3.2. Torrefaction
The torrefaction process is defined as a thermal treatment at
temperatures between 200 and 300 °C and a reaction time between
946
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F. Santos Dalólio et al.
doi:10.1017/S0043933910000656.
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30 and 180 min at atmospheric pressure to prevent spontaneous
combustion of the treated fuel [93,94]. Torrefaction improves the
contents of moisture, carbon, hydrogen and calorific value, with
particles presented more homogeneous shape and size [95]. Although
advantageous, there are still no studies on torrefaction of poultry litter
to be used as fuel, indicating a new field of studies to improve the
properties of this material as biomass energy.
9. Conclusions
Poultry litter is presented as an extremely valuable residue and is
generated in large quantities in poultry production due to the
significant expansion of the global poultry industry. When used as an
organic fertilizer damage has been observed from an environmental
and social point of view, because of its indiscriminate and excessive
use. In this sense, the processes available for energetic use of poultry
litter are presented as a viable alternative to the poultry sector. Among
the thermochemical processes are direct combustion, gasification,
pyrolysis and co-generation mechanisms with other biomasses, which
are effective from both technical and environmental points of view to
generate useful energy, either in the form of heat, work, kinetic energy
or electricity. In addition to the energy generation alternative, thermochemical processes act as appropriate treatment methods, eliminating
pathogens and microorganisms present in poultry litter. However,
greater attention should be given to the proper disposal and use of the
produced ash.
Transformation processes of poultry litter into energy should be
extremely well controlled by computer modeling in order to prevent
harmful air emissions to the environment and negative effects to
human health. Furthermore, use of poultry litter as biomass energy
for thermochemical processes may be feasible only in regions where
this residue has highly availability and is frequently produced. This is
due to the costs of acquisition and transportation of biomass, and its
respective moisture content, which are the main points relevant to the
financial viability of a sustainable business. Poultry litter is a heterogeneous waste and does not have a standardized composition, therefore
new studies must be developed to assess its use for energetic purposes,
and also verify its effect during long-term utilization.
Acknowledgements
The authors would like to thank the Federal University of Viçosa,
CAPES, Cnpq and Fapemig.
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