=Paper=
{{Paper
|id=Vol-2030/HAICTA_2017_paper21
|storemode=property
|title=Relevant Biogas Substrate – Maize Silage vs Slaughterhouse Waste
|pdfUrl=https://ceur-ws.org/Vol-2030/HAICTA_2017_paper21.pdf
|volume=Vol-2030
|authors=Anna Smurzyńska,Jacek Dach,Kamil Kozłowski,Jakub Mazurkiewicz,Ewa Woźniak,Boniecki Piotr,Karol Kupryaniuk,Damian Janczak,Michał Brzoski
|dblpUrl=https://dblp.org/rec/conf/haicta/SmurzynskaDKMWB17
}}
==Relevant Biogas Substrate – Maize Silage vs Slaughterhouse Waste==
https://ceur-ws.org/Vol-2030/HAICTA_2017_paper21.pdf
Relevant biogas substrate – maize silage
vs slaughterhouse waste
Anna Smurzyńska1, Jacek Dach1, Kamil Kozłowski1, Jakub Mazurkiewicz1, Ewa
Woźniak1, Piotr Boniecki1, Karol Kupryaniuk2, Damian Janczak1, Michał Brzoski1
1
Institute of Biosystems Engineering, Poznan University of Life Sciences, Wojska Polskiego
50, 60-637, Poznan, Poland, e-mail: jdach@up.poznan.pl
2
Department of Food Process Engineering, University of Life Sciences in Lublin,
Doświadczalna 44, 20-280 Lublin, Poland
Abstract. The lack of support for construction and operation of installation of
biogas plants in Poland makes looking for cheap and efficient substrates. The
most commonly used substrate is maize silage. This is related to the high
biogas efficiency and the advanced technology of its extraction. The problem,
however, is the cost of buying the silage by the biogas plants, which has
grown considerably in recent years, due to its wide use. It finds food
applications, is a rich nutrition source for animals but is also the most
commonly used substrate in the production of renewable energy for
production of bioethanol as well as in biogas fermentation. As a result, maize
is a desirable substrate on the market. This paper indicates the possibility of
using of post-slaughter waste in biogas plants. The methane fermentation of
these waste materials allows them to be safely disposed of, so that these
substrates can be obtained for a small fee or even for free. Slaughterhouse
waste materials have also shown high biogas and methane efficiency and are
therefore the substrates desired in the anaerobic biodegradation process. It
should be noted, however, that these substrates require additional thermal
treatment prior to application into the fermentation chamber, which reduces
the potential income for the biogas plant..
Keywords: biogas, maize silage, slaughterhouse waste, methane efficiency
1 Introduction
In a biogas plant, the right choice of the substrates is a key element influencing the
kinetics of overcoming methane fermentation. The basic factor is the content of dry
matter and dry organic matter. An important issue is the purity of the substrate, i.e.
lack of foreign bodies in the form of stones or sand. The bacterial microflora plays
very important role in the methane fermentation process, so selected substrates
should be free from bactericidal and pathogenic organisms or chemicals that prevent
the functioning of anaerobic bacteria. An important issue in the selection of
substrates for biogas plants is the cost of their acquisition, availability and location of
the source of their acquisition. (Kozlowski et al., 2016; Wiecek and Tys, 2015).
Basic substrate used in biogas plants are waste materials from animal husbandry.
These are faeces of livestock in the form of manure and slurry. An application of the
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manure is to feed the fermentation mixture with dry matter and dry organic matter. In
turn, the slurry, despite its low energy value, has a number of functions in the
methane fermentation process. It is a diluting fermentation mixture substrate,
consisting of the materials with higher dry matter content, which are the source of
biogenic substances for microorganisms responsible for the production of methane.
Rich bacterial microflora of the slurry makes it also an inoculant, especially for
methanogenic bacteria. Slurry has buffering properties, which make it possible to
manage many hazardous substances in the environment, allowing for the stability of
the process in progress (Smurzyńska et al. 2016). Moreover, the management of
animal waste in the methane fermentation process enables their safe disposal, which
allows the protection of soils, waters and against uncontrolled and dangerous gaseous
emissions (Smurzyńska et al. 2015, Smurzyńska et al. 2016a, Smurzyńska et al.
2016b, Smurzyńska et al. 2016c).
Further, most commonly used substrates in biogas plants are the materials of plant
origin. The most commonly used plant is maize, and its silage. In 2012, 241590.19
megagrammes of this substrate (ARR 2014) were used for biogas purposes. Szlachta
and Fugol (2009) highlight the efficiency of methane fermentation process based on
slurry and maize silage. In the fermentation process, vegetable and fruit residues and
their pulp are also commonly used. The use of these vegetable products is due to the
properties they exhibit during the anaerobic process and biogas and methane
efficiency.
Methane fermentation also makes it possible to efficiently dispose the substrates that
are potentially hazardous to the environment. Many of the biodegradable byproducts
from industry and agri-food sector may be successfully used in biogas plants, which
will also allow for safe manure production (Czekała et al., 2012). Among these
products, sewage sludge should be mentioned (Carmona and Dach 2015), banned for
storage since 2016 and therefore requiring proper management. Other burdensome
substrates are slaughter waste, the number of which increases with the development
of farm holdings. The use of these dangerous substrates in biogas plant is
increasingly used not only because of the increasing amount of hazardous substrates,
but also because of the potential for safe disposal while achieving economic
profitability.
This article has compared the use of maize silage in biogas plant as the substrate
most commonly used with the substrate that pose a threat to the environment.
1.1 Maize silage characteristic
Maize is an important and most productive crop in the world. Both in Europe and
Poland, the economic importance of maize is high and growing (Michalski 2004,
Szmigiel et al., 2012). In Poland, maize cultivation is widespread throughout the
country and the cultivated area is more than 1.2 million hectares (Central Statistical
Office, 2016).
It is possible to distinguish two main directions of cultivation of this plant: grain and
silage. Maize is used for consumption and industrial purposes and for the feeding of
farm animals. In recent decades, along with the development of renewable energy,
both grain (bioethanol) and silage (methane fermentation) have been used for
197
bioenergetic purposes (Fugol and Prask, 2011). It should be noted that while the area
devoted to maize cultivation in Poland in order to obtain maize silage is over 555
thousand, in case of Germany it amounts to 900 thousand. ha.
Fig. 1. The area of cultivation of maize for silage (thousands ha) (Central Statistical
Office, 2016)
This is due to the fact that maize silage is a basic substrate used in biogas plants, the
number of which in Germany has increased significantly in the last decade. Due to
the new possibilities of maize application, special energy varieties have been created
which allow for optimum biomass yield (Atletico K 280, Cannavaro K 310, Cassilas
K 260, Fernandez K 250, Kaifus K 300, Krabas K 290, Ronaldinio K 260, Touran K
230). Maize varieties used in the methane fermentation process intended for silage
contain higher amount of structural polysaccharides. In turn, maize intended for
silage in order to obtain valuable feed is characterized by more starch content.
It should be marked that the content of components during the maize development,
affects the amount of methane produced. In the early stages of maize vegetation, the
parts of plants are formed that contain structural carbohydrates, i.e., raw fiber. In the
later period during the grain formation, the starch is stored there. The increase in the
amount of starch and lignin-cellulosic compounds during vegetation causes the raw
material to be less susceptible to methane fermentation, which results in lower yields
on the substrate. Literary sources report that obtaining valuable maize silage for
methane fermentation takes place at a dry matter content of 28-35% for the entire
plant. The maize in this period is in the phase of making flasks and filling them with
the grains. Its biomass is characterized by the most optimal content of raw protein,
raw fiber and its components (i.e. cellulose, hemicellulose and lignin as well as
starch and sugar) for biogas purposes.
If maize silage is used as a substrate in biogas plants, the costs of maize growing are
significantly important. Maize is a plant resistant to temperature fluctuations, so it is
suitable for the climate in Poland. However, the decrease in yield during drought is
198
noted. The maize cultivation allows for a very high yield of green mass from 1 ha,
which is important due to the high and constant demand for filling the fermenting
chambers. This plant is easy to ensilage and is characterized by lower acquisition
costs compared to other cultivated plants. The techniques for maize growing and
harvesting are also widespread, due to the use of maize for food purposes and to
provide cattle feed (Szlachta, 2009).
It is also important to achieve high levels of methane and biogas production from
maize silage during anaerobic biodegradation. This results from a high dry matter
content (on average 28%) and dry organic matter (on average 90%), so it is
considered as an energy crop (Niedziołka and Zuchniarz, 2007). Maize silage is a
substrate free of harmful organic substances and heavy metals (Schattauer et al.,
2005), which are responsible for the inhibition of the methane fermentation.
In order to use maize silage in biogas plants, it is required to store it properly and it is
therefore necessary to provide storage plates for this substrate. This allows the
protection of ecosystems and the purity of the substrate, which is important in the
fermentation process. Maize silage is stored in prisms under foil cover. In turn,
dosing into the fermentation tank is done using a conveyor belt.
In order to use maize silage as a substrate for fermentation mix, the cost of obtaining
this substrate should be taken into account. As highlighted, maize is a multi-
directional-use crop, so that cultivation for a biogas substrate becomes competitive
with respect to silage used for food and feed purposes. This leads, to the gradual
increase of the price, which is noted with the development of renewable energy.
Studies of Szlachta and Tupiek (2013) show that profitability of maize for silage as a
substrate for biogas plants depends on the level of yield and the costs of cultivation,
harvesting and silage. Moreover, the authors also highlight the need to ensure
competitive prices both for the farmer and the biogas plant. Studies have proved a
higher income for maize cultivated for grain.
1.2 Slaughtery waste characteristics
The basic characteristic of slaughterhouse waste is the high content of organic
compounds, so that they are naturally biodegradable. These waste materials are the
source of carbohydrates, proteins, fats and biogenic substances essential for the
development of microorganisms. In view of the above, in case of lack of
management, these waste materials constitute a serious threat to the environment.
Slaughter waste is a source of serious health hazards, due to potential development of
pathogenic microflora. By disposing of decomposition they are responsible for the
burdensome odor emissions that arise during storage. Moreover, improper storage
may lead to leaching of leachate effluents consisting of biogenic compounds (nitrate,
phosphate and potassium) to soil and water, disrupting the ecosystems balance
(Sobczak and Błyszczek, 2009).
The slaughter waste indicates high biogas and methane efficiency that result from
increased lipid content compared to plant material. Fats are a source of high carbon
and hydrogen content, which makes them a high potential for methane production. It
should be noted, however, that the presence of fats also contributes to the reduction
199
of methanogenic activity and biomass adsorption. As a result, lower levels of
degradation and longer HRT are observed.
According to the EU law, three categories of slaughter waste are distinguished
(Regulation of the European Parliament and the Council (EC) 2009). Category I
requires unconditional disposal of waste at the incineration plant and is unsuitable for
utilization in methane fermentation. Slaughter waste from category II and III can be
processed by anaerobic fermentation in biogas plants, after prior thermal treatment
under additional conditions.
2 Materials and methods
2.1 Substrates used in experiment
The research material was maize silage. The slaughter waste was also used for the
study. These were homogenized waste materials from category II and category III.
In order to investigate the biogas and methane efficiency, a fermentation inoculum
containing the desired groups of organisms was required. Inoculum, which is the
separated liquid fraction of the fermentation pulp from one properly functioning
agricultural biogas plant, was used in the performed experiment. The following
methodology was used according to the Polish Standards: PN-90 C-04540/01 for pH
determination, PN-EN 27888: 1999 for conductivity, PN-75 C-04616/01 for dry
matter and PN- Z-15011-3 in case of organic dry matter.
2.2 Experimental set-up
The research on methane efficiency of the substrates in batch culture technology was
carried out in the Laboratory of Ecotechnology at the Institute of Biosystems
Engineering (PULS) on the basis of internal procedures, based on adapted standards:
DIN 38 414-S8 and VDI 4630, commonly used in Europe. Detailed methodology of
performed research was presented by Cieślik et al. (2016)
3 Results and discussion
At the beginning of the experiment the basic physicochemical parameters of the
investigated substrates were defined in order to determine the proportion of
individual components in the fermentation mixtures. Table 1 shows the dry matter
content and dry matter content of the substrates. Both silage and slaughter waste
show a high dry matter content and thus require an application of additional dilution
substrate (Owczuk et al. 2014).
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Table 1. Parameters of analyzed substrates
D.M. O.D.M.
Substrates
[%] [%]
Maize silage 31.74 95.92
Slaughtery waste, cathegory II 49.85 98.12
Slaughtery waste, cathegory III 36.59 96.50
Table 2 represents the methane and biogas efficiency of investigated substrates. A
high biogas yield is noted in case of slaughter waste. The highest production of
methane and biogas was noted in particular when using category II waste, which was
at the level of 407.27 m3·Mg F.M. and 586.48 m3·Mg F.M..
In turn, the least efficient substrate turned out to be maize silage, which is the most
commonly used co-substrate in biogas plants, among others, in Poland. For maize
silage, over 5 times lower methane production and more than 4 times lower biogas
production has been noted, compared to waste from category II, in calculation for
fresh matter. In contrast, waste from category III have been reported to account for
almost 4-fold lower methane production and 3-fold lower biogas production, also in
calculation for fresh matter.
Comparing the biogas and methane efficiency of the tested substrates calculated on
dry matter, the higher methane efficiency of slaughterhouse waste has been noted,
more than 3 times, as well as twice higher the biogas efficiency in relation to maize
silage.
Table 2. Methane and biogas efficiency of tested substrates
Cumulated Cumulate Cumulated Cumulated
Methane
methane d biogas methane biogas
content
[m3·Mg-1 [m3·Mg-1 [m3·Mg-1 [m3·Mg-1
[%]
F.M.] F.M.] D.M.] D.M.]
Maize
53.40 75.92 142.18 261.50 489.74
silage
Slaughter
waste - 69.45 407.27 586.48 816.99 1176.49
category II
Slaughter
waste - 69.10 294.67 426.30 805.33 1165.08
category III
In case of investigated substrates, the price of maize silage is 25-35 €/Mg, whereas
slaughter waste materials are the substrates for disposal, so the biogas plant receives
a recycling fee of 5-100 €/Mg (depending on the waste type). Consequently, the
possibility of utilizing of slaughter waste in biogas plants is of mutual benefit. For a
meat factory that transfers waste to environmentally safe disposal without incurring
costs. And in turn, the biogas plant adopts a burdensome substrate, which is also a
valuable source of energy production.
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The biogas and methane efficiency shown by slaughter waste represents the potential
for high energy production in biogas plant. If maize silage is used which shows
significantly lower biogas and methane efficiency, it should also be marked that the
cost of this substrate purchasing should be taken into account, which considerably
decreases the income of the planned investment. Therefore, it is proposed to use
maize straw silage to maintain the viability of the plant (Cieslik et al., 2016).
4 Conclusions
In many biogas plants the primary substrate except the slurry is corn silage. This is
due to the biogas and methane efficiency of the substrate and methane fermentation
run, which is devoid of the inhibitor of the process. The development of biogas
energetics has forced cultivation of maize with higher content of dry matter and
reduced starch content. Moreover, maize is a high yielding plant with resistance to
temperature changes, which makes it one of the main crops in Poland. The wide
range of maize applications makes the growing and harvesting techniques also
widespread. However, use of maize in food industry and the possibility of energetic
support of biogas plants, causes that the purchase price of this substrate entails less
and less interest in using it for energy purposes. As a result, other substrates are being
sought that will allow the profitability of the biogas plant, especially in case of such
low subsidies for investments in renewable energy installations in Poland. It is
proposed to use biodegradable waste materials from industry and agriculture. This
article proves very high biogas and methane efficiency of slaughterhouse waste.
However, it should be highlighted that despite the free substrate acquisition by the
biogas plants, they also require additional thermal treatment, resulting in higher
investment and operating costs of biogas plants.
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