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http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦70♦ No. 6 ♦2019
2058
Renewable Energy Production Potential by using from Wastes
Generated in a Pigs Farm and Slaughterhouse
RUFIS TAGNE TIEGAM FREGUE1,2, ADRIANA RALUCA WACHTER2*, IOANA IONEL2, TEODOR VINTILA3, CALIN JULEAN3, SEBASTIAN MOISA3,
CLAUDIU ION UNGUREANU1, ALIN CRISTIAN MATIUTI1
1 Research Unit of Noxious Chemistry and Environ. Eng., Dep. of Chemistry, Faculty of Science, University of Dschang, P.O.Box 67, Dschang,
Cameroon
2
Politehnica University of Timisoara, Mechanical Engineering Faculty, 1 Mihai Viteazu Blvd., 300222, Timisoara, Romania
3
University of Agricultural Science and Veterinary Medicine King Michael I of Romania from Timisoara - Department of Biotechnologies,
119 Calea Aradului, Timisoara, Romania
Biogas produced from wastes is regarded as advanced biofuel and is under current EU regulation,
promoting the growth of advanced biofuels. In this study, the authors focused the research on the
potential of a pig farm and an adjacent slaughterhouse and meat processing enterprise to produce not
only meat, but energy as well, through anaerobic digestion of wastes produced during current activities
to produce biogas as energy carrier. One had assessed the potential of a pig’s farm and an adjacent
slaughterhouse and meat processing enterprise to produce biogas as energy carrier, using anaerobic
digestion of wastes generated in production activity. All experiments were carried out on a performing
lab device. The results indicate solid sludge and fats resulted from slaughterhouse are capable to
produce high yields of methane, reported to dry organic matter. Although organic wastes resulted from
slaughterhouse can generate high quantities of methane by anaerobic digestion, large quantities of
organic wastes are generated in the assessed pig’s farm and the potential for energy production is
much higher in the case considering as source the pig’s farm than slaughterhouse. Finally, one
demonstrated that by combining organic wastes generated in the pig’s farm with the organic wastes
resulted from slaughterhouse, or organic wastes generated in the pig’s farm with the biomass produced
on 200 hectares of triticale as short rotation crop, one can supply the energy source, necessary to
operate an one-megawatt installed power biogas plant.
Keywords: renewable energy, biogas, organic wastes
Green energy will be the core of post-petroleum society and the bio-
based economy. Despite all controversies, biofuels do and will continue
to constitute a major share in green energy sector. Advanced biofuels
represent all solid, liquid and gaseous combustible materials generated
from biological non-feed and non-food renewable resources. Organic
waste materials are primarily considered to contain huge unused
potential to be converted in green energy. Burning materials containing
large quantity of water is not economically efficient, or in terms of
energy balance.
Biological conversion processes, as fermentation or anaerobic
digestion (AD) have numerous advantages, such as: high energy
balance, low carbon emissions, in many cases produces no wastes,
high economic efficiency, positive social impacts in rural areas etc.
Anaerobic digestion has even more particular advantages, as it is a
natural
process, made by microorganisms present on Earth since early
times of beginning of live, it uses existent microbial biodiversity, there
is no necessity to genetically alter microorganisms involved in this
process, once inoculated - the process runs theoretically forever if
process parameters and feeding rate are well controlled. Anaerobic
digestion is probably the most appealing process to be applied in
agricultural farms in order to convert organic wastes produced during
farming activities into energy and - not less important - into organic
fertilizer.
In this study, we have assessed the potential of a pigs farm and an
adjacent slaughterhouse and meat processing enterprise to produce
not only meat, but energy as well, through anaerobic digestion of
wastes produced during current activities to produce biogas as energy
carrier. Biogas produced from wastes is regarded as advanced biofuel
and is under current EU regulation promoting the growth of advanced
biofuels. In January 17th 2018 EU Parliament adopted RED II
(Renewable Energy Directive), by which all EU countries must ensure
that at least 10% of their transport fuels come from renewable sources
by 2020 and that minimum share of advanced biofuels to be gradually
increased from at least 0.5% in 2021 to at least 3.6% in 2030 [1].
Experimental part
Materials and methods
The organic wastes were sampled and investigated in the
Laborator y of Industrial Microbiology and Biotechnology from University
of Agricultural Science and Veterinary Medicine King Michael I of
Romania from Timisoara. The first analyses were made to establish
dry mater content and organic load. Based on the results, suitable
Fig. 1. General overview of AMPTS system:
1- bioreactors/digesters, 2- incubation unit,
3- gas counters, 4- CO2 absorption unit, 5- methane
measuring unit, 6- laptop for data recording
* email: avram_adriana21@yahoo.com
REV.CHIM.(Bucharest)♦70♦No. 6 ♦2019 http://www.revistadechimie.ro 2059
recipes for anaerobic digestion (AD) were calculated, and were
subjected to AD process by using AMPTS II laboratory equipment, in
order to point out the Biochemical Methane Potential (BMP) of the
sampled organic materials. The conversion of biomass to biogas was
tested according to the widely accepted German standard protocol
VDI 4630 [2].
Sampling and investigation
Sampling, sample transportation and conservation as well as
sample preparation are integral components of the testing digestion of
organic materials and exercise a decisive influence upon the quality
of the results. All sampling procedures for the investigated organic
materials (substrates) were conducted according to standard methods
[2-5]. For fermentation tests seeding sludge was used as inoculum,
provided from a large scale biogas plant.
Samples were collected from a pig farm and from a slaughterhouse,
as follows:
1 -Animal fats from slaughter house (AF)
2 -Waste-water from slaughter house pumping station (WW)
3 -Solid sludge from slaughter house (SS)
4 -Pigs slurry from storage tank (PST)
5 -Pigs slurry from pumping station (PSP)
6 -Triticale silage (energy biomass, as control) (TS)
7 -Inoculums -harvested from a functional on-farm biogas plant (I).
Previous to AD experiment set up, it is necessary to investigate the
dry solids (DS) and volatile solids (VS) of substrates. The dry matter,
i.e. all inorganic and organic compounds, is expressed as DS and was
measured according to standard protocols, by keeping samples 24 h
on 105 ºC in order to remove all water content [2, 3].
The VS is represented by organic compounds in the sample. After
completing the DS measurements, heating the sample up to 550 ºC for
2 hours, it was necessary to burn up the organic matter. The weight
difference between the sample after heating at 105 ºC and 550 ºC
indicates the VS content of the substrate [3].
Laboratory equipment used is an Automatic Methane Potential Test
System - AMPTS II, developed by Bioprocess Control Sweden AB (BPC),
which has 15 digesters of 600 ml total volume. For high accuracy
experimental data records, the BMP (Biochemical Methane Production)
investigated for each sample was achieved as triplicates, according
to BPC protocol [4].
The investigated samples and quantities used in the present
experiment were prepared according to standard protocol VDI4630
and BPC [2, 4].
The general overview of the laboratory equipment is presented in
figure 1. The batches were subjected to mesophilic digestion, at
incubation temperature of 37
o
C. Before the beginning of the incubation,
all 15 bioreactors were flushed for approx. 60 s with a gas mixture of
45 % CO
2
and 55 % N
2
by volume. The digestion process is ended
when the biogas yield decreases less than 1 % (by volume) from the
total biogas yield.
Results and discussions
The decision whether organic residues resulted in pigs farming
and meat processing can be converted by anaerobic digestion to
produce methane at large scale is dependent by the results obtained
in laboratory scale, in the biochemical methane production (BMP) test
carried out in this AMPTSII system. The results provided by this test are
proved to be very reliable and the method is applied world-wide to
establish the amount methane released during anaerobic digestion of
organic matter [6, 7]. The volume of methane generated in BMP test is
expressed in units of volume in standard temperature and pressure
conditions, i.e. 0
o
C (or 32
o
F) and 1.013 bar (or 14.69 psi). These
reference conditions are stated as
normal conditions
and are indicated
by underlying letter N in the unit of volume used (e.g.
ml
N
). Knowing
the energy density of methane, the BMP test is used to establish the
amount of methane and consequently the energy produced in mixtures
of several organic substrates. This calculation can be used to establish
the amount of incentives offered in cases of energy production from
waste materials versus dedicated crops etc.
In Romania, the support scheme, in the frame of green energy
legislation establish different numbers of green certificates to be granted
for biogas plants producing electricity [8]. The biogas plants producing
electricity from energy crops are granted with one extra green
certificate per each 1 kWh delivered to the grid if compared with the
biogas plants producing electricity from wastes [9].
One recommends to the biogas producers to analyze and establish
by BMP test the potential amount of bio-energy produced from wastes
and from energy crops. The results can be delivered to the energy
authority, which establish the amount of green certificates provided to
the biogas producer, according to amount of bio-energy [9, 10].
The results regarding preliminary analyses of pigs wastes used in
our study, inoculums and triticale as an example of short-period energy
crop are presented in table 1.
Table 1
PROPERTIES OF INVESTIGATED SUBSTRATES, BY WEIGHT
Fig. 2. Methane yields during
anaerobic digestion
http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦70♦ No. 6 ♦2019
2060
By using the CO
2
absorption unit (fig. 1), data recorded represents
gas volume of CH
4
recorded in milliliters under normal conditions
(mL
N
). These data represent the average values of daily methane
production of methane generated in each triplicate consisting of three
600 mL digesters containing 400 mL digestion medium. The inoculum
/ substrate ratio in all batches was 2:1, in terms of volatile solids. For a
clearer picture regarding flow rates and gas methane dynamics, the
recorded data are plotted in the graph in figure 2.
Data in figure 2 reveal a high production of biogas when the mixture
of energy crop and inoculum from a large-scale biogas plant is used as
substrate (triticale silage). Organic wastes generated in both locations
– pigs farm and abattoir produce important quantities of methane
although lower than energy crop used as control.
When data generated in the laboratory scale digesters are used in
BMP test, methane yields are reported to mass of organic matter. BMP
test is a simple batch assay developed to determine the methane
production of a given organic substrate during its anaerobic
decomposition. BMP is defined as the volume of the methane produced
per amount of organic substrate material added to the bioreactor,
subtracting the methane generated by the inoculum [4, 11].
From BMP calculations for each type of substrate data
resulting indicate the highest methane yields in solid sludge
and fatty residues generated in abattoir. The late substrate
generates similar yields as energy crop triticale (fig. 3).
the company operating the pigs farm and the slaughter house. Following
conclusions are resulting:
1.In the case of
Fat substrate
, the farmer has no possibility to provide
exact quantity generated during 12 months activity. In this case, we
calculated the amount of energy to be generated by 10 tons of fatty
residues resulted from slaughter house activities. If the quantity can be
assumed by the farmer to a closer range, the calculation can be easily
corrected.
2.In case of
energy crops
(triticale silage), the authors’ assumption
provide data useful to compare the energy to be produced when 100
or 200 hectares of agriculture land is cultivated with a crop able to
store a medium quantity of energy in short time (it can be cultivated as
short rotation crop). One didn’t proposed and used high-energy
production crop, such as corn silage, because this culture needs
agriculture land for an entire production cycle. Also better usage for
this corn is known, as food.
Data generated in the research and presented in table 2 indicate
that the organic fraction generated during one year of activity in slaughter
house can generate similar amount of energy if is an aerobically
digested comparing to the energy that can be obtained from 200
hectares of land cultivated with energy crops (in this case triticale).
Regarding organic wastes generated in the farm, our
results indicate triple amount of energy obtainable by
converting these materials to methane, comparing to
organic wastes from slaughter house. According to data in
table 2, the necessary installed power of a suitable
cogeneration heat and power unit (CHP) to convert the
annual energy for 8400 working hours per year can be
calculated. Subsequently, the scenarios in table 3 can be
considered.
Table 3
INSTALLED POWER OF CHP UNITS NECESSARY TO CONVERT THE BIOGAS INTO POWER AND THERMAL ENERGY
Fig. 3. BMP from different yields
By comparing data presented in figures 2 and 3, one might be
tented to conclude that some inadvertences are resulting.
It can be observed that despite of the high BMP potential of fats
substrate, the methane generation in fats batch digester is much lower
than in the case of the pig slurry or mixture.
These differences are due to the dilutions necessary to be done
when feeding digesters with certain amounts of organic loads.
Economic aspects
The results generated by the laboratory tests and further analyses
and calculations were used to quantify the amount of energy to be
generated on-site.
The calculation is based on quantities of organic materials
generated during a 12 months period, most of data being provided by
Table 2
ANNUAL ENERGY PRODUCTION
REV.CHIM.(Bucharest)♦70♦No. 6 ♦2019 http://www.revistadechimie.ro 2061
The scenarios in table 3 present a clear view regarding the potential
of energy production from organic residues by anaerobic digestion.
Our assessment indicates that conversion on-site of diluted abattoir
residues is not an efficient option, as high capital and operational costs
are needed to convert large quantity of diluted waste-water to produce
low quantity of energy.
A more efficient option is to transport the separated sludge and fats
from the waste water treatment plant (w.w.t.p.) of the slaughterhouse
to the pigs farm (scenario 3) and convert the mixture of farm wastes
and w.w.t.p. sludge and fats to biogas. The conversion can be made in
simple digesters as covered lagoons or mixed and covered storage
tanks.
A close-range quantity of energy (enough to feed a 900 kW
e
CHP
unit) can be obtained if ensiled triticale obtained from around 100
hectares of land is added to the digester containing the organic wastes
from pig farm. A surface of around 200 hectares of agricultural land
cultivated with triticale as catch-crop (short rotation crop) is sufficient
to be added to organic wastes from pigs farm to feed a one-megawatt
CHP unit.
Further calculations can be carried out if additional data are provided
by the farmer:
-one-year energy demands of the farm / abattoir as electricity and
thermal energy equivalent as natural gas consumption. These data
can be compared to the expected energy production rate by AD
process.
-acquisition price of the energy, in order to be compared to the
estimated production costs of the energy by AD.
Finally the investments costs and annual costs can be calculated
for a CHP unit dimensioned in accordance to the EU procedures for
financial of agricultural biogas projects.
Primary Energy Savings (PES) indicators can be calculated in
accordance to the EU legislation protocols. The annual income and
savings can be established in different possible scenarios for the energy
recovery [17]. Annual incomes can be calculated in correlation to total
annual costs and annual savings. By analyzing the PES indicator values,
different scenarios could be tailored to find out if, according to the EU
legislation, the energy is produced in high efficiency unit [18, 19]. This
fact decides if an investment into biogas plant is eligible for EU funding
or not.
Conclusions
One has evaluate the potential of a pig’s farm and an adjacent
slaughterhouse and meat processing enterprise to produce biogas
that can be used as energy carrier, by using anaerobic digestion of
wastes generated in the mentioned production activities.
The results indicate that solid sludge and fats resulted from
slaughterhouse are producing high yields of methane reported to dry
organic matter.
Large quantities of organic wastes are generated in the assessed
pig’s farm and the potential for energy production is much higher in the
case of pig’s farm than in the case of using waste from the slaughterhouse.
Combining (1) organic wastes generated in the pig’s farm with the
organic wastes resulted from slaughterhouse, or (2) organic wastes
generated in the pig’s farm with the biomass produced on 200 hectares
of triticale as short rotation energy crop, one can supply the feedstock
necessary to operate an one-megawatt installed power biogas plant.
Thus a waste producer can turn into an energy producer, mainly the
energy being used for internal necessities.
Acknowledgement:
This work was concluded by Adriana Raluca W
achter
, in
her position as PhD student at the Politehnica University of Timisoara. The university is
acknowledged for the support. Many thanks to the staff of the Pig Farm (Smithfield) for
all information and testing materials provided during the research for the present papers.
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