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EVALUATION OF THE ENERGY POTENTIAL OF URBAN SOLID WASTE PRODUCED
IN THE CITY OF THROUGH THE ANALYSIS OF LANDFILL AND INCINERATION
PROCESSES.1
Vasco Munguare Penente
Author’s affiliation, Mozambique
Abstract: `
The growth in the generation of urban solid waste, driven by the increase in population density, has generated
negative impacts on the natural and social environment. One of the alternatives to minimize the impacts caused by
solid urban waste is the energy use of this waste. This work aims to estimate the energy potential of urban solid
waste generated in the city of Beira. In which the theoretical energy potential of the waste produced in the city of
Beira, through the incineration and landfill biogas processes, was estimated. The energy potential was determined
based on the data obtained through the bibliographic survey, corresponding to the characteristics of the MSW, and
the amount of waste generated daily provided by the Municipality Council of Beira (CMB). Based on the data
obtained, the generation of biogas was estimated using the LandGEM 3.02 model and also the energy recovery
using equations that describe the total theoretical energy generated through the incineration process. The results
showed that the incineration of MSW would generate 166150.54MWh/year and avoid the emission of 323000
tCO2eq/year. Biogas recovery would generate 22565.67MWh/year and avoid the emission of 7681.98
tCO2eq/year. MSW can be used as an alternative source of energy and its energy use can contribute to better
waste management, minimizing the negative impacts generated by waste on the environment and society.
Keywords: Energy recovery, Incineration, Biogas, MSW.
Corresponding author:
_______________________________________________
1. Introduction
Excessive population growth is accompanied by an
increase in the use of fossil fuels and an increase in
waste produced daily. The increase in the generation
of urban solid waste along with the processes of
urbanization of cities creates a problem that is
currently widely discussed, bringing great concern in
Using Solid Wastes of Tikrit City to Produce Electric Energy
relation to the damage that inefficient management
can cause to the environment and civil society.
Data on waste management in sub-Saharan Africa are
scarce. This scarcity of data results mainly from the
lack of waste management activities in countries. Case
studies in Ghana, Zimbabwe and Botswana show that
the increasing volume of waste is often faced with a
lack of financial, technical and institutional resources
(KARANI, 2008). Likewise, waste management is
still at a low level in Mozambique. Most activities are
centered in larger cities, especially around Maputo –
the country's capital. Smaller cities and rural areas
suffer from insufficiencies in all aspects of solid waste
management, i.e. collection, transport, treatment, final
disposal, as well as a lack of basic sanitation
(KARANI, 2008). Diseases such as cholera,
meningitis and dysentery are often associated with the
lack of proper waste disposal (FERRÃO, 2006).
Mozambique is one of the least developed countries in
the world. Its' human development index was ranked
181st out of 188 countries in 2015 (UNDP, 2016).
However, its gross national income per capita
increased by around 24% between 2010 and 2015. As
the economy starts to grow, so do environmental
problems. Waste management is one such area that
has become a bigger issue that has a direct impact on
the environment.
Previous research has identified lack of knowledge
and insufficient service infrastructure as the main
reasons behind inadequate waste management
practices in Mozambique (FERRÃO, 2006).
The organic fraction of the waste is naturally degraded
over time in the landfill. The deterioration of waste in
dumps or landfills causes the emission of various
gases, including two of the main causes of the
greenhouse effect, methane gas (CH4) and carbon
dioxide (CO2). (FANTOZZIA& BURATTI, 2009).
The city of Beira has a daily production of waste
estimated at 523 tons (CMB, 2016), with these as final
destination a dump where the waste is disposed of in
the open, where its deterioration causes gas emissions.
The importance of using these gases to remove them
from landfills and convert them into energy,
preventing them from being released into the
atmosphere, is emphasized. Another factor that makes
this use interesting is the economic gains it can
provide for its use in the generation of electricity
(MAZZONETTO 2016).
The use of energy used to meet the demand for energy
combines benefits such as economic and
environmental within a solid waste management
system, and therefore this present study seeks to
estimate the energy potential of urban solid waste
from the city of Beira to the extent the population of
the city grows.
1.2. Objectives
12.1. General:
• Estimate the energy potential of urban solid waste
produced as a function of population growth.
1.2.2. Specifics:
• Carry out a survey, quantification and energy
recovery of solid waste generated in the city of Beira.
• Determine the energy recovery potential through
solid waste incineration and landfill processes.
• Estimate avoided emissions by using incineration
and landfill technologies.
2. Material and Methods
3.1Generation per capita
Knowing the total amount of waste generated daily, it
is possible to determine the per capita generation
value of MSW in the city through the equation
g=Q_RSU/P Equation (1)
g: generation per capita (kg/dayinhab)
Q_RSU: amount of MSW generated daily (t/day)
Q: number of inhabitants.
3.2. Arithmetic method
This method assumes a constant population growth
rate for the following years, based on known data, for
example, the population of the last census
(FERNANDES, 2009). If ka is a constant and
considering P_1 the population of the penultimate
census (year t_1), P_2 the population of the last
census (year t_2), t the year for which we are
projecting and P the population in year t, we arrive at
the general expression from the arithmetic method:
P=P2+ka(t−t2)
Equation (2)
Where the constant k is found by the equation
ka=(P_2-P_1)/(t_2-t_1 ) (3) P_2=533825
inhabitants
P_1=443369 inhabitants
t_2= 2017
t_1= 2007
Substituting the values in equation 5, we have
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Using Solid Wastes of Tikrit City to Produce Electric Energy
ka = 9045.6 Substituting the values in equations 2
we have: P= 579053 inhabitants
Substituting the values in equation 1 g= 0.90
kg/day.hab
3.3. Gravimetric composition
The average gravimetric composition of solid waste
from the city of Beira is presented in the table
Table 1: Average gravimetric composition
Percentage Component (%)
Organic matter………………….. 49.2
Paper/cardboard ………………….13
Plastics……………………………. 17
Fabric/rubber………………………. 5
Metal………………………………. .3
Glass………………………………..7.2
Wood……………………………….. 5
Other…………………………….… 0.6
Source: Average values calculated from
(PENENTE & LÍGIA, 2016)
3.4 Estimate of MSW energy recovery in the city of
Beira through the incineration process
Among the various heat treatment technologies, the
study analyzes incineration and landfill. The first
consists of a controlled combustion process, having as
its basic principle the reaction of oxygen with
combustible components present in the waste, at a
temperature above 800° C, converting its chemical
energy into heat that can be transformed into
electricity through cycles at steam.
For the energy valuation of MSW, it is necessary to
evaluate the energy contained in it, namely, the lower
calorific value (PCI), since for incineration the MSW
fractions that have a high calorific value are of
interest, such as plastics, paper/cardboard, etc.
(FEAM, 2012)
3.5. Determination of the energy content of Beira
MSW
The energy contents of Beira MSW were
determined from the equation PCI_i=PCI.Y Equation
(3)
Where: PCI_i: lower calorific value contained in
each MSW fraction (kcal/kg); PCI: lower calorific
value of each type of waste (kcal/kg); Y: portion of
the component present in MSW (%). (FEAM, 2012)
Table 2: Lower calorific value of some waste 3.6 Determination of energy generation potential by
incineration of MSW
For the determination of the theoretical total energy,
which can be obtained from the MSW generated in the
city of Beira, the Equation was used:
ET=PCItotal . η. Q RSU .
Equation (4)
Substituting the values from table 1, corresponding to
the gravimetric composition and in equation 3, we
have:
Table 3: Theoretical energy content of fractions and
total MSW in the city of Beira
Where:
E_T: theoretical total energy in kWh/day
PCI_total: total lower calorific value of MSW
(kcal/kg); η: electrical efficiency
Q_RSU: amount of waste generated daily in Beira
(kg/day) k: conversion factor from kcal to kWh (k =
0.001163)
3
MSW Components Calorific value
Paper 4030
Organic matter 1310
Textiles 6300
Plastic 6300
Rubber 6780
Wood 2520
MSW Components Energy content of MSW
from the city of
Beira (kcal/kg)
Paper 523,9
Organic matter 644,52
Textiles/rubber 513
Plastic 1071
Wood 126
Total energy
content
(Kcal/kg)
2878,42
Source: (the author, 2022)
Using Solid Wastes of Tikrit City to Produce Electric Energy
According to FEAM (2012) the average electrical
efficiency of MSW incineration plants is 26%.
Substituting the values in equation 7
E_T = 455206.98 KWh/day
E_T = 166150.54MWh/year
For the determination of the total theoretical power,
the Equation was used:
P=ET
t
Equation (5)
Where t: time in hours of daily use of the incinerator
plant (24 hours) Substituting the values in the
equation. P=18966,95kW= 18,96MW
3.7 Estimated energy recovery from landfill biogas
To estimate the energy recovery of MSW through
landfill biogas, the LandGEM program (Landfill Gas
Emissions Model) - version 3.02 was used.
LandGEM is a program developed by the Control
Technology Center of the EPA (Environmental
Protection Agency) (EPA, 2007).
The program uses a first-order equation to estimate
gas emissions for the desired year.
QCH4=∑
i=1
n∑
j=0,1
1
k Lo(Mi
10 ¿¿)e−ktij ¿¿
Equation(6)
Q_CH4: annual methane production for a given
year (m^3/t) i: 1- increase per year n: year of
calculation (initial year of landfill opening)
j:0.1- increase per year
k: methane generation rate (year^-1)
L_0: waste methane generation potential (m^3/Mg)
Mi: mass of waste received in the year in each
section (Mg)
tij: year, in each section, of receipt of the mass of
waste (time, with decimal precision, for example, 3.2
years)
The parameters Lo and k are the most important, as
they reflect variations according to location, climate
and type of waste. According to Figueiredo (2012)
this model can be used both for site-specific data and
with standard data to estimate gas emissions in
landfills.
3.8. Calculation of parameters k and L_0
The methane generation rate (k) and the methane
generation potential (L_0) are parameters of great
importance for estimating methane gas, as they reflect
the reality of generation at the landfill over the years.
According to USEPA, (2004), the value of k can be
calculated from the equation:
k=3,2×10−5× Pma +0,01
Equation (8)
Where:
Pma= Average annual precipitation (mm) Since the
average annual precipitation in the city of Beira is
935mm, (INAM, 2022) substituting the value in
equation (7) we get the following result: k=0.039
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Using Solid Wastes of Tikrit City to Produce Electric Energy
According to IPCC (2006), one way to calculate the
potential for methane generation, used in this research,
is through the equation
L0=FCM × COD × CODf× F × 16
12
Equation (7)
Where:
FCM: methane correction factor (%)
COD: degradable organic carbon (Gg of C/Gg of
MSW); CODf: fraction of COD dissociated (%);
F: volume fraction of methane (%); 16/12: carbon to
methane conversion factor (Gg de 〖CH〗_4/Gg de C);
According to IPCC (2006), the value of the methane
correction factor for proper and well-managed waste
disposal is 1.
The default value, recommended by the IPCC (2006),
for the dissociated degradable organic carbon fraction
is 0.5.
The value of the methane volume fraction (F) was
considered equal to 0.5, since, according to IPCC
(2006), the biogas generated in a landfill by solid
waste has a percentage of 50% methane.
Degradable organic carbon (DOC) is the organic
carbon in the waste that is accessible to biochemical
decomposition. COD is estimated based on waste
composition and can be calculated from a weighted
average of the carbon content of various degradable
components (waste types / materials) of the waste
stream (IPCC, 2006).
(COD)_i: fraction of degradable organic carbon in
waste type i and Wi: fraction of waste type i by waste
category
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Using Solid Wastes of Tikrit City to Produce Electric Energy
The value of 〖COD〗_i depends on the composition of
the material that will be deposited in the landfill and
can be seen in Table 4.
COD=∑(CODi× W i)
Substituting the values in the equation COD = 0.1608
Having the COD, we can already calculate the
methane generation potential through equation (6),
L0=FCM × COD × CODf× F × 16
12
L0=1×0,1608×0,5 ×0,5 ×16
12
L0=0,0536≫de CH 4/¿de RSU
Considering the density of 〖CH〗_4 (0^° and 1.013
bar) as 0.0007168 t/m^3(FIGUEIREDO, 2012). One
has:
L_0=74.77m^3 〖CH〗_4/ ton of waste
To estimate landfill biogas generation through
LandGEM, it was necessary to estimate the amount of
solid waste that will be aggregated over the 20 years
of the landfill's useful life, as a function of population
growth and per capita MSW generation.
3.9 Population estimate
To estimate the population growth of the city of Beira,
data from the 2017 census (533,825 inhabitants) were
used. The future population forecast was calculated
using the arithmetic method, previously used to
determine the 2022 population figure.
3.10. MSW generation estimate
To estimate the amount of waste that will go to the
landfill, the equation
Pd=pop × g × R
1000
Equation (8)
Where:
Pd: average daily production of waste (kg/day)
Pop: population in the given year considered
g: per capita generation of city waste
(kg/person.day)
R: percentage of waste landfilled (%)
It was assumed that the percentage of landfilled waste
will be 100%.
3.11. Calculation of available power and energy
The determination of the available power can be done
through the equation (POLETTO, 2009)
P=Qx. PCImetano . η
860000
Equation(9)
Where:
P: power available each year (MW)
Q_x: methane flow each year (m^3 〖CH〗_4/h)
〖PCI 〗_methane: calorific value of methane =
8500kcal/m^3 〖CH〗_4 Conversion factor: 1 kcal/h=
(1/860000) MW η: landfill efficiency
According to Martins (2014), the conversion of
biogas into electricity is done using an internal
combustion engine coupled to a generator and has an
efficiency that varies from 20 to 50%. Therefore, the
value of 30% was adopted for landfill efficiency.
To calculate the available energy, the equation
E=P. Rend .T
Equation (10)
Where
E: available energy (MWh/day);
P: available power (MW);
Rend: motor efficiency operating at full load = 80%
(adopted)
T: engine operating time (24 h/day). Emissions
avoided by the energy use of MSW
The emission of gases avoided by the energy use of
MSW can be estimated by the Equation
Eev =Ee. E pEquation(11)
Where: Eev: avoided
emission (t CO2eq/year); Ee: technology-specific
avoided emission (tCO2eq/MWh); Ep: Electric
energy produced annually (MWh/year).
6
Table 4: Degradable organic carbon content for
each MSW component
MSW Components COD (% mass unit)
Paper/ cadboard 40
Organic matter 15
Textiles/rubber 40
Wood 30
Source: (Rezende, 2022)
Using Solid Wastes of Tikrit City to Produce Electric Energy
4.0. Results and Discussion
Table 5: Population and MSW generation estimates
Year Populaon Per capita MSW/day MSW(t/year)
2023 588099 0,90 529,28874 193190,3901
2024 597144 0,90 537,42978 196161,8697
2025 606190 0,90 545,57082 199133,3493
2026 615235 0,90 553,71186 202104,8289
2027 624281 0,90 561,8529 205076,3085
2028 633327 0,90 569,99394 208047,7881
2029 642372 0,90 578,13498 211019,2677
2030 651418 0,90 586,27602 213990,7473
2031 660463 0,90 594,41706 216962,2269
2032 669509 0,90 602,5581 219933,7065
2033 678555 0,90 610,69914 222905,1861
2034 687600 0,90 618,84018 225876,6657
2035 696646 0,90 626,98122 228848,1453
2036 705691 0,90 635,12226 231819,6249
2037 714737 0,90 643,2633 234791,1045
2038 723783 0,90 651,40434 237762,5841
2039 732828 0,90 659,54538 240734,0637
2040 741874 0,90 667,68642 243705,5433
2041 750919 0,90 675,82746 246677,0229
2042 759965 0,90 683,9685 249648,5025
2043 769011 0,90 692,10954 252619,9821
As shown in table 5, population growth in the city
of Beira will lead to an increase in the amount of
urban solid waste generated,
The potential for generating electricity through the
incineration process depends on the calorific value of
the fuel, an element that even determines the technical
viability of its use.
7
Using Solid Wastes of Tikrit City to Produce Electric Energy
According to (EPE, 2008), the MSW classification
based on the PCI should not be considered definitive
for determining the final destination of waste, it is
considered that:
• For PCI <1,675 kcal/kg, incineration is technically
unfeasible (in addition to technical difficulties, it still
requires the addition of auxiliary fuel),
• For 1,675 kcal/kg <PCI> 2,000 kcal/kg, the
technical viability of incineration still depends on
some type of pre-treatment that increases the calorific
value;
• For PCI > 2,000 kcal/kg, mass burning is
technically feasible.
Based on the gravimetric composition of MSW
from the city of Beira obtained through a
bibliographic review, the lower calorific value of
MSW generated in Beira was estimated at 2878.42
kcal/kg. kcal/kg), which allows mass burning without
the need to add combustible material in order to raise
the calorific value to the minimum technically.
Tabela 6: Estimation of methane generation through the LandGEM Software.
Year
m3CH4/year
m3CH4/h
2023 0 0
2024
553583,18 63,19
2025
1094506,91 124,94
2026
1623255,41 185,30
2027
2140294,37 244,33
2028
2646071,67 302,06
2029
3141018,06 358,56
2030
3625547,82 413,88
2031
4100059,37 468,04
2032
4564935,91 521,11
2033
5020545,96 573,12
2034
5467243,97 624,11
2035
5905370,82 674,13
2036
6335254,33 723,20
2037
6757209,82 771,37
2038 7171540,53 818,67
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Using Solid Wastes of Tikrit City to Produce Electric Energy
2039
7578538,10 865,13
2040
7978483,01 910,79
2041
8371645,03 955,67
2042
8758283,60 999,80
2043
9138648,23 1043,22
2044
9512978,90 1085,96
2045
9149114,20 1044,42
2046
8799167,07 1004,47
2047
8462605,17 966,05
2048
8138916,52 929,10
2049
7827608,74 893,56
2050
7528208,26 859,38
2051
7240259,63 826,51
2052
6963324,83 794,90
2053
6696982,60 764,50
Source: (the author, 2022)
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Using Solid Wastes of Tikrit City to Produce Electric Energy
Graph 1: Production of gases in the sanitary landfill
Biogas generation depends on the amount of waste
deposited, analyzing table 6 and grap1 related to
biogas generation, it is observed that the maximum
methane generation occurs in the year 2044, one year
after the end of the useful life of the landfill , with a
total of 9512978.90 m^3/year. During the useful life
of the landfill, the curve shows an increasing behavior
of biogas generation, the gas production increases as
more waste is deposited in the landfill over the years
and from the point where it reaches its maximum
value, the curve decays, since the landfill no longer
receives MSW and gas generation occurs through the
decomposition of residual organic material.
Table 7: Available power and energy based on methane generated each year
Year Methane()
m3CH4/h
Power(MW) Energy
(MWh
/year)
202 0 0 0
202 63,19 0,19 1313,15
202 124,94 0,37 2596,27
202 185,30 0,55 3850,51
202 244,33 0,72 5076,98
202 302,06 0,90 6276,73
202 358,56 1,06 7450,79
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Using Solid Wastes of Tikrit City to Produce Electric Energy
9
203 413,88 1,23 8600,14
203 468,04 1,39 9725,72
203 521,11 1,55 10828,45
203 573,12 1,70 11909,20
203 624,11 1,85 12968,81
203 674,13 2,00 14008,09
203 723,20 2,14 15027,81
203 771,37 2,29 16028,73
203 818,67 2,43 17011,56
203 865,13 2,57 17977,00
204 910,79 2,70 18925,70
204 955,67 2,83 19858,32
204 999,80 2,96 20775,46
204 1043,22 3,09 21677,72
204 1085,96 3,22 22565,67
204 1044,42 3,10 21702,55
204 1004,47 2,98 20872,44
204 966,05 2,86 20074,09
204 929,10 2,75 19306,27
204 893,56 2,65 18567,82
205 859,38 2,55 17857,61
205 826,51 2,45 17174,57
205 794,90 2,36 16517,65
205 764,50 2,27 15885,87
Source: (the author, 2022)
From the annual values of biogas obtained through
the LandGEM software, the available power and the
11
Using Solid Wastes of Tikrit City to Produce Electric Energy
possible electrical energy to be generated were
calculated, in which through the results (table 7) it is
observed that the power and the energy generated are
directly proportional to biogas flow into the landfill
and decay from the moment the landfill is closed.
As the maximum generation of biogas, maximum
power generation and maximum energy generation
occurs in the year 2044, one year after the closure of
the landfill. Even after the useful life of the sanitary
landfill there is still methane generation due to the
organic matter present in solid waste and
consequently, there is generation of electrical energy,
which can still be used.
As for energy generation, incineration is the
alternative that provides the greatest generation
potential, and in turn avoids more gas emissions
compared to the landfill biogas process, and
incineration can avoid around 323. 103 tCO2eq/year
while landfill biogas could avoid the emission of
7681.98 tCO2eq/year in the city of Beira.
4. Conclusion
Of the various technologies for the energy use of
urban solid waste, the two exposed technologies
require the use of specific criteria that must be used in
decision making.
Urban solid waste produced in the city of Beira has a
great energy potential, can generate about
166150.54MWh/year by the incineration process and
22977.42 MWh/year by energy recovery through
landfill biogas, thus minimizing the impacts caused by
the waste. The use of energy can avoid emission of
323. 103 tCO2eq/year through incineration and almost
7700 tCO2eq/year through landfill biogas, which
would be a great contribution in the fight against
climate change and at the same time increase energy
production provided to the city.
The two waste energy recovery technologies present
possibilities of contributing to the energy matrix of the
city of Beira, from an alternative source of energy,
and mitigating a current problem in the city as well as
in the country, such as inadequate waste disposal.
References
[1]FEAM. Aproveitamento energético de resíduos sólidos
urbanos: guia de orientação para municípios de Minas
Gerais. Belo Horizonte : s.n., 2012.
[2]FERNANDES, J. G. Estudo da emissão de biogás em um
aterro sanitário experimental. Escola de engenharia da
Universidade Federal de Minas Gerais, UFGM. 2009
[3] Ferrão DAG Avaliação da remoção e eliminação
dos resíduos sólidos na Cidade de Maputo, Moçambique
(Evaluation of removal and disposal of solid waste in
Maputo City, Mozambique). (2006)
[4] FERRAZ, J. L. Modelo para avaliação da gestão
municipal integrada de resíduos sólidos urbanos. Faculdade
de Engenharia Mecânica, Universidade Estadual de
Campinas – UNICAMP, 2008.
[5]22. KARANI P, Da Costa J (2007) The role of
knowledge in improving waste management for sustainable
development: The case of Maputo Mozambique.
[6]PENENTE & LIGIA, Gestao urbana e ageraçao de
Energia electrica.Beira, 2016.
[7]33. POLETTO, J. A. Incineração de Resíduos Sólidos
Urbanos e Geração de Energia, Aspectos Energéticos e
Económicos. São Paulo : s.n., 2009
[8]FIGUEIREDO, J. C. Estimativa de Produção de Biogás e
Potencial Energético dos Resíduos sólidos Urbanos em
Minas Gerais. 2012
[9]EPA. 2007. U.S. Enviromental Protection Agency. EPA.
2007.
[10] FANTOZZIA, F.; BURATTI, C. Biogas production
from different substrates in an experimental Continuously
Stirred Tank Reactor anaerobic digester .Bio resource
Technology. Volume 100, Issue 23, December 2009.
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