José Carlos Souza Oliveira
FATEC - São Paulo, Brazil
E-mail: jcso2009@gmail.com
Submission: 03/01/2017
Accept: 13/01/2017
ABSTRACT
Biomass
is one of the largest sources of energy available in agribusiness activities.
Anaerobic biological degradation of organic matter, present in swine manure,
produces a gaseous mixture of methane (CH4) and carbon dioxide (CO2).
Anaerobic
biodigestion is one of the most effective methods for the treatment of manure,
obtaining as biogas products; Substitute for some fuels; and biofertilizer;
Rich in nutrients and applied in agriculture.
The
conceptual simplicity of biodigestors does not bring light, the great
complexity of chemical and physical processes. One of the main reasons for this
complexity is the expressive amount of variables that must be monitored to
guarantee better efficiency of these equipments. Among these variables, the
values of biomass temperature, amount of gas generated, pH, residence time,
among others, stand out.
Aspects
related to the Logistics of transport and storage of biomass to Process Control
methods, plus Cultural aspects, Professional Training, Creation of public
policies, Maintenance of biodigesters, are challenges in the application of
biodigestion for energy generation from waste Pigs on an agroindustrial scale.
The objective of this article is to analyze
some factors that represent challenges to the application of biodigestion
process for energy generation from swine waste on an agroindustrial scale, thus
contributing to important reflection on the design and installation of
biodigesters in agroindustrial activities.
1. INTRODUCTION
Brazil has one of the largest swineherds in the world, which consequently
generates large amounts of organic waste in the production chain. In view of
this scenario, the biodigestion process presents itself as an alternative for
the treatment of these wastes, because in addition to reducing the polluting
potential and sanitary risks of the waste, it allows the generation of two
products: biogas, which can be used as Source of renewable energy and
biofertilizer that can be used as fertilizer in agriculture. Largely employed
in small farms, the application of the biodigestion process in agroindustry
presents some difficulties.
In
this context, this article presents the analysis of some factors that represent
a challenge to the application of biodigestion process for energy generation
from swine waste on an agroindustrial scale.
2. RESEARCH METHODOLOGY
As for its purpose, this research is classified as Applied Research, because the knowledge acquired will be used for practical application focused on the solution of real problems.
As
to nature, this research is classified as Abstract of Subject, because it is
based on more advanced works.
From
the point of view of its objectives, this research is classified as
Exploratory, since it aims to provide more information about the subject under
study.
As for the object, this research is classified as Bibliographic research, since
it was elaborated from material already published.
3. REVIEW OF THE LITERATURE
3.1.
Pig
waste: an environmental issue
The production of swine animal waste
is a major issue to be solved along the production chain of Agroindustry.
Exposed to high temperature these waste produce highly polluting and harmful
gases to society and to the environment.
To
get an idea of the size of this problem Diesel et al. (2002), reports that a
swine head produces a volume of waste (liters/day) equivalent to the volume
generated between 10 to 12 people, and its polluting power in Biochemical
Oxygen Demand, corresponds to the production of domestic sewage of 100 people.
According
to Lima (2011), the amount of substrate varies according to the economic
activity and the scale of production of a rural property (animal waste and crop
residues) or an agroindustry (effluent with high organic material load and
diversified composition).
For Diesel et al. (2002), swine
manure, urine, water wasted by drinking fountains and sanitation, feed
residues, hair, dusts and other materials resulting from the breeding process.
The substrate in turn consists of animal faces, which contains organic matter,
nitrogen, phosphorus, potassium, calcium, sodium, magnesium, manganese, iron,
zinc, copper and other elements included in animal diets.
According
to Oliveira (2004) in the following table, we can observe the average daily
production of manure, mixture of manure and urine and liquid waste by pigs in
each production phase.
Table
1: Average daily production of swine manure per phase
Source: Adapted from Oliveira (2004)
It is observed that for pigs the average
daily production of waste can reach 18 kg per animal. For cattle, it is
estimated that every 1 liter of cows produce 3 kg of waste.
Considering a large rural
property, we can have the dimension of urgency to reuse this biomass as a raw
material to reduce environmental impacts and the urgency to face the challenge
of waste with intelligence and ecologically correct actions.
According
to Oliveira (2004), one of the major problems in animal confinement systems for
slaughter is the amount of waste produced daily in a reduced area. The disposal
of waste from animal facilities has lately been a challenge for breeders and
specialists, since it involves technical, health and economic aspects.
Such
waste, if handled improperly, can cause negative impacts to the environment.
For Seganfredo (2000) the excess of waste
in the soil can cause accumulation of nutrients, generating chemical imbalance
resulting in a fall in cereal productivity, intoxication of animals by certain
nutrients in forage (for example, copper is harmful to sheep), fall In the
quality of vegetables by heavy metals and excess of nitrogen in the soil.
Lima (2011) states that the
environmental damages are even greater when these organic wastes are dragged
into the watercourses because they have a high Biochemical Oxygen Demand (DBO),
reducing the oxygen content of the water. In addition, the various nutrients
contained in these residues, mainly Nitrogen (N), Phosphorus (P) and Potassium
(K), stimulate the growth of aquatic plants and the accumulation of decomposing
organic matter in water bodies (Eutrophication).
According
to Perdomo (2001), the discharge of untreated pig effluents from soil, rivers
and lakes is a potential risk for the appearance of diseases such as verminoses
, Hepatitis, hypertension, stomach cancer, among others; Besides the discomfort
of the population due to the proliferation of flies, rubber trees, bad smells
and degradation of natural resources, due to fish and animal death, plant
toxicity and eutrophication of water resources.
In view of this scenario, it is
necessary to treat these wastes by removing or transforming these pollutants so
that they can be reused in the soil or disposed of safely. For Kunz et al.
(2004), before considering any treatment system, attention must be paid to the
production system, where waste treatment must be seen as an integral part of
the production process, so everything that is done inside agroindustrial
facilities can Have positive or negative influences in the treatment of waste.
Factors such as dilution of waste, nutrition of animals with low feed
conversion ratio, use of antibiotics and detergents, training of personnel
responsible for the operation of the systems, has a direct influence on the
treatment of waste.
The treatment of the waste can be
carried out in a physical or biological way. For Diesel et al. (2002), the
physical treatment promotes the separation of the liquid portion from the solid
portion of the waste. This separation can be done by decantation,
centrifugation, sieving and / or pressing, and dehydration of the liquid part
by wind (forced air or heated air). On the other hand, the biological treatment
consists of the biological degradation of the substrates by aerobic and
anaerobic microorganisms, resulting in a stable material and free of pathogenic
organisms. For solid waste, composting is an example, and for liquid waste the
stabilization, digestion and biodigestion lakes can be highlighted.
3.2.
Characterization
of swine animal waste
According to Lima (2011), the use of
swine animal waste is economically feasible to produce energy and fertilizer,
but adequate for the management of this waste, adequate planning, within the
scale of production.
According
to Cortez et al. (2008), the characterization of the substrate must be
performed by a series of physical, biochemical and chemical parameters, aiming
to identify a series of parameters to evaluate the organic load of the
substrate and its behavior during the degradation stages of organic matter,
when submitted to Anaerobic digestion process, allowing to determine the
production of methane and also to model the efficiency of the process.
For
Lima (2011), among the physical parameters, the most important are quantity, density,
size, viscosity and solids content. The amount of substrate varies according to
the economic activity and scale of production of a rural property or an
agroindustry.
According
to Lucas Júnior et al. (2003), the availability of agricultural residues in
Brazil has increased in the last decade due to the evolution of animal protein
production. The following table shows the approximate yield of the biogas
production, according to the type of substrate.
Table 2: Methane production for different
substrates
Source: Lucas Júnior et al. (2003)
It
can be observed that the best yield (m3 / kg) is for the manure of dairy
cattle, due to its confinement, the pigs have a yield of 4 times less, about
0.1064 m3 / kg.
Density
is another important physical parameter. For Lima (2011), its knowledge is
important for the sizing of the system of pumping and storage of liquid
substrates.
Another parameter is the
size of the particles, as it allows evaluating the distribution and the
dilution of the substrate in water, as well as the percentage of dissolved
particles, in suspension. This data varies according to the type and the
handling given to the substrate. Also for Lima (2011), the factors that affect
the size of the animal waste particles are diet, age, and species and breed
(subspecies) animal, as well as the place of creation. The inadequate site may
favor contamination of the substrate with the presence of dust, feed residue,
hair, and sawdust, shavings, among other contaminants, as well as the
management and storage of the waste.
The
viscosity which, as well as the density, is also directly related to the
substrate handling and the design of the pumping system from the substrate
origin site to the anaerobic reactor, allows to know their respective flow rates
according to the amount of dry matter Diluted in the substrate.
Finally,
for the value of the solids content, according to Lima (2011), this allows to
identify the materials dispersed in liquid mixtures or to know the percentage
of Moisture in solid materials. The classification of the solids content may be
physical or chemical. Physically, they are classified according to their
dimensions.
According
to Diesel et al. (2002) to determine, the quality of the substrate should be
used reliable and significant parameters, the Biochemical and Chemical
parameters allow evaluating the digestibility of the substrate, which directly
affects the efficiency of an anaerobic biodigestor. For pork, the main
parameters are: Biochemical Oxygen Demand (DBO), Chemical Oxygen Demand (DCO),
Total Organic Carbon (COT) and Dissolved Oxygen (OD).
• DBO (biochemical oxygen demand - mgO2 / L): corresponds to the need for
oxygen that purifying bacteria need to digest polluting loads in water.
Oliveira (1993) states that pollution
of the environment in the swine producing region is high because, while the DBO
content for domestic sewage is 200 mg.L-1, the DBO value of swine manure can
vary from 30,000 to 52,000 Mg.L-1, that is, pollutant potential of up to 260
times higher than domestic sewage.
• DCO (chemical oxygen demand - mgO2 / L): to determine the amount of oxygen
needed to oxidize organic and inorganic matter present in water, without the
intervention of microorganisms.
According
to Kunz and Oliveira (2006) for swine effluents the DCO reference value used
should be 66,900 ± 13,500 mg.L-1 of DCO.
• COT (Total Organic Carbon): the COT analysis allows the identification of
the amount of carbon originating from living organisms present in the
substrate.
According to Lima (2011) the
objective of this parameter is to quantify the Carbon element present in a
substrate; Be dissolved and / or suspended. In relation to the DBO and DCO
analyzes, the COT analysis is performed in a shorter period of time and at a
lower cost, however, its result does not replace the importance of the DBO and
DCO analyzes, since they are complementary for determination of the load Of a
substrate.
• OD (Dissolved Oxygen): According to Von Sperling (2005), dissolved oxygen
(DO) is a fundamental element for the maintenance of
Organisms. It is a parameter of characterization of the effects of the
pollution of the water bodies by organic matter releases. The presence of
organic matter in aquatic systems favors the development of microorganisms that
will consume the OD until it is exhausted, creating anaerobiosis conditions.
According to Von Sperling
(2005), determining the percentage of OD in the substrate that will be consumed
by the microorganisms, before starting the anaerobic digestion process, is
fundamental to evaluate the initial speed of the anaerobic digestion process,
since its presence in the Substrate is characterized as inhibiting element of
the process.
Still according to Diesel et al. (ST
- mg / L), Volatile Solids (SV - mg / L) and Total Nitrogen (NT - mg / L),
should also be considered in the characterization of swine manure.
•
Total solids (ST - mg / L): correspond to
the solid matter contained in the waste after removal of moisture;
•
Volatile solids (SV - mg / L): Corresponds
to fraction of organic material;
•
Total Nitrogen (NT - mg / L): corresponds
to the nutrients present in the waste, such as nitrate, nitrite, ammonia and
organic nitrogen.
The following table shows the variation of
DBO as a function of the material content.
Table 3: Variation of DBO of liquid waste
as a function of dry matter content
Source: Adapted from Dartora et al. (1998)
For
Dartora et al. (1998) the production system used in each farm is that it
characterizes the degree of dilution of the waste, the volume, as well as its
physical, biochemical and chemical properties, before identifying and designing
a waste treatment system, one must do an analysis of the farm, taking.
Consideration of how to feed the animals, types of drinkers, handling and cleaning system.
The following table presents
references in the literature for parameters of pig substrates:
Table 4: References for some parameters for
finishing substrates of pigs
Source:
Adapted from Moffitt (1999), Merkel (1981) and Konzen (1983)
Pigs
weighing between 18 and 100 kg, with a mean production of 63,40 kg / d / 1000
kg, with an average moisture content of 90%, are considered to be finishing
pigs.
3.3.
Routes
of conversion biodigestion: Concept, process and history
For Alves et al. (2010), the
biodigester is an equipment where the fermentation of the organic matter by the
bacteria happens in a controlled way, reducing the environmental impact and
generating fuel of low cost. The process of decomposition of organic matter
results in two products: biogas and biofertilizer.
The process of anaerobic digestion is divided into 4 steps: hydrolysis,
acidogenesis, acetogenesis and methanogenesis.
In the first stage of the process,
called Hydrolysis, according to Li et al. (2012) involves the reduction,
through enzymes, of complex organic polymers to simple soluble molecules.
According Li et al. (2012), bacteria are not able to
assimilate particulate organic matter, the complex organic matter is
transformed into simpler soluble compounds, a process that occurs by the action
of the extracellular enzymes excreted by the fermentative bacteria. In parallel
proteins are hydrolyzed to form amino acids, sugars are formed from hydrolysis
of carbohydrates and soluble lipids are hydrolyzed to fatty acids.
Still second, Li et al. (2012) states that
hydrolysis is a critical rate limiting step that determines the biomass
feedstock conversion efficiency.
Eckenfelder
(2000) argues that the reduction in the size and complexity of the particles
does not imply a reduction of organic load, since the monomers are converted to
fatty acids with small amounts of H2.
In
the second stage of the process, called Acidogenesis, the biodegradation of
bacteria occurs, which may be obligatory anaerobic or facultative anaerobic,
known as acidogenic.
For Versiani (2005), the main
products formed are acidic, butyric acid, acetic acid, lactic acid, carbon
dioxide, hydrogen sulfide (H2S), hydrogen (H2), and new microbial cells.
According to (BOHRZ, 2010) most acidogenic bacteria are strict anaerobes, but about
1% of them consists of facultative bacteria, which can oxidize the organic
substrate aerobically. This important fact, except that the dissolved oxygen,
possibly present in the medium, could become a toxic substance for the later
stage of degradation.
In
the third stage the Hydrogenogenesis or acetogenesis according to Oliva (1997)
is the stage where the volatile acids and the alcohols are metabolized,
producing acetate and H2 by means of acetogenic bacteria producing H2. H2-acting
or homoacetogenic acetogenic bacteria convert part of H2 and CO2 that do not
combine to form methanol and acetate.
In the case of methanobacteria, the
presence of hydrogen peroxide and carbon dioxide in the acidic phase of the
methanobacteria is the main cause of the reaction.
Finally,
the stage of Methanogenesis, according to Chernicharo (1997), is the final
stage of the process of anaerobic degradation of organic compounds in methane
and carbon dioxide, being carried out by means of methanogenic microorganisms.
Due to its substrate affinity and magnitude of methane production. Methanogens
are divided into two main groups, one that forms methane from acetic acid or
methanol, and the second that produces methane from hydrogen and carbon
dioxide.
The
following table summarizes the steps in the biodigestion process:
Table 5: Phases of the biogas production process
Source:
Adapted from Eder and Schulz (2007)
3.4.
Control
Parameters of the biodigestion process
The anaerobic processes alter with environmental changes, being necessary
to control the factors that affect the performance of the bacteria, thus
optimizing that of the biodigestion process of organic residues.
Among the several factors that
influence the activity of methanogenic bacteria, it is possible to highlight the
amount of water content (dry matter), nutrient concentration, pH, internal
temperature of the digester, retention time, solids concentration Volatiles,
the carbon / nitrogen ratio and the presence of toxic substances inside the
biodigester.
According to Neves (2010), the
amount of water used should be about 90% of the total biomass content,
depending on the type of biomass. The dilution ratio should be around 1: 1 to
1: 2. The excess or lack of water is harmful to the system.
For
Neves (2010) the lack can cause clogging in the pipeline and the excess can
disrupt the hydrolysis process, because a high biomass load is required for it
to be correctly processed.
For Nutrient Concentration, Neves (2010) warns that
improved efficiency of biological processes requires the availability of
essential nutrients for microbiological development in adequate proportions.
Minimal nutritional requirements can be estimated from the empirical
composition of microbial cells.
Pinto (1999) states that the
process of bacterial degradation will also be related to the availability of
nitrates, phosphates and sulfates. The presence of essential nutrients, such as
iron, and micronutrients, such as nickel and cobalt, in appropriate
concentrations improve the process and biogas production, also when the residue
to be degraded presents a higher Chemical Oxygen Demand ( DCO)
The knowledge of the chemical composition and the type of biomass, by
means of its correct characterization, is very important, since it can be
enriched with fertilizers and chemical activators, if necessary, denominated
inoquos, acting as accelerating element and correcting properties of the
substrate.
With respect to Ph-control, changes
during the process considerably affect the bacteria involved in the digestion
process. Among the interference factors of anaerobic digestion, acidity and
alkalinity are important factors, since microorganisms are living beings that
need to be in a medium that favors their development and performance.
For Neves (2010), there is no ideal
pH for the performance of the microorganisms in the biodigestion process,
however it is recommended that the pH be in the range of 6 to 8, and it may be
considered optimal in the range of 7 to 7.2, which normally occurs when the
digester is working well.
For the temperature factor of the
digester, Denis and Burke (2001) states, that temperature is a very important
variable during anaerobic digestion, influencing the whole process of bacterial
performance. The higher the temperature, higher biogas production and may
influence the concentration of biogas components.
When the temperature is adequate, the activity level of the
microorganisms is higher and the organic components decompose rapidly.
According to Neves (2010), the
bacteria responsible for biodigestion are very sensitive to sudden changes in
temperature (variations of 3ºC are enough to cause the death of most digestive
bacteria), there is no consensus between the exact temperature for each group
of bacteria.
For Neves (2010) retention
Time is the time at which any substrate passes inside a digester, ie the time
between the inlet and outlet of the different materials of the digester. The
retention or digestion time varies depending on the characterization of the
substrate, such as biomass type, grain size, digester temperature, biomass pH,
etc.
According
to Neves (2010), the retention time can vary from reaction to reaction. Usually
it takes from 30 to 45 days, but in some situations, it is possible the
existence of the biogas soon in the first week of hydraulic retention in
smaller proportions; Phenomenon observed, mainly in continuous biodigesters.
According to Pinto
(1999), the production of biogas and the process of organic matter degradation
are directly affected by the composition of the residue, for a higher
concentration of volatile solids, implying a greater amount of matter
Degradation, thus increasing the amount of gas produced.
The carbon / nitrogen
ratio according to Lenz (no date) is an important parameter and it is related
to the conditions in which the biological process of the fermentation takes
place, being the carbon / nitrogen ratio ideal for an optimal digestion values
between 20 to 30: 1, I.e., 20 to 30 parts of carbon to one of nitrogen. Most
strains of animals, including pigs, present low C / N ratios because they have
a lot of nitrogen and must be corrected with vegetable residues such as straws,
sawdust, sawdust, etc. to reach the ideal point.
3.5.
Products
generated from the biodigestion of the pig substrate
The
products that are generated from biodigestion are: biofertilizer and biogas.
The
biofertilizer is a product of the biodigestion process, which optimizes the use
of the pig substrates, adding value to the agroindustrial chain.
Barichello, et al. (2011)
states that after the biogas production, the fermented biomass leaves the
interior of the biodigestor in liquid form, with a large amount of organic
material, that can be used for soil fertilization. With the application of this
biofertilizer in the soil, there is an improvement in the biological, chemical
and physical properties of the soil, surpassing any other alternative of
chemical fertilizer.
Barichello, et
al. (2011), further states that due to the process that occurs in biodigestion,
organic matter (biomass) loses exclusively carbon, in the form of methane gas
(CH4) and carbon dioxide (CO2), increasing the nitrogen
and other nutrients content . As it works as a soil acidity broker,
biofertilizer, unlike chemical fertilizers, improves soil quality, better
absorbing soil moisture, resisting long periods of drought.
For Rodrigues (2010) the
biofertilizer can be disposed to the soil "in natura" or processed.
The advantage of the processing is in storage and transport gains, since it
stops storing and transporting water, which part returns to the process in the
correction of the moisture of the incoming waste and part goes to the
atmosphere in the form of water vapor.
The composition of the
biofertilizer may vary according to the type of biomass used in the
biodigester. The following table presents this composition for swine manure.
Table 6: Components of the biofertilizer from
swine
Source: Adapted from
Barichello (2011)
The value of the benefits of biofertilizer in farming is as important as the application of biogas in agro-industrial processes.
For Alves (2010) the biogas is
constituted by a mixture of gases, whose type and percentage vary according to
the characteristics of the residues and the working conditions of the digestion
process. The main constituents of biogas are methane and carbon dioxide. The
characteristic composition is approximately 60% methane, 35% carbon dioxide and
5% of a mixture of hydrogen, nitrogen, ammonia, hydrogen sulfide, carbon
monoxide, volatile amines and oxygen.
For Deublein
and Steinhauser (2008); Other gases, such as nitrogen (N2),
oxygen (O2), traces of hydrogen (H2) and hydrogen
sulphide (H2S).
Alves (2010) describes
methane as a highly combustible and flammable gas, producing a light blue flame
and its burning produces little or no pollution. It is a colorless gas, being
one of the final products of the anaerobic fermentation of substrates of
animals like pigs. In energy terms, the larger the amount of methane, the
better the gas.
The following table shows the
average values of biogas production per kilo of fermented material. The
materials included in this table are only the materials of greater availability
in the rural environment.
Table 7: Biogas generation capacity
Source: Adapted from
Barichello (2011)
It
is observed that the gas production potential of pigs is only lower than the
potential of equines and birds, but the availability of this waste is much
higher.
According to Arruda (2002),
biogas can have its energy power used in the same process, as in cooking,
heating, cooling, lighting, incubators, feed mixers, motor fuels,
refrigerators, stoves, water heaters Electricity, among others. The production
of biogas, starting from the biomass, begins to take place around 20 days.
4. CHALLENGES IN THE APPLICATION OF BIODIGESTÃO IN
AGROINDUSTRIAL SCALE
The first applications of
biodigestion in Brazil began in the 70's, these experiments demonstrated that
it was possible to produce biogas and biofertilizer, using simple technologies.
In the following decade, with the creation of the PME (Energy Mobilization
Program), incentives for the installation of biodigesters, through financing or
even donations of the necessary resources to the installation; Intensified the
application of biodigestion.
According
to Palhares (2008), at the time, some factors were responsible for the failure
of the application of this technology, among which we can mention:
•
Underestimation of the biogas production potential;
•
Inadequate management of crops and crops;
•
Lack of technical knowledge and design errors;
•
High cost of implementation and maintenance;
•
Lack of adequate equipment;
•
Materials used in construction with a low useful life;
•
Lack of specific environmental legislation.
It
is clear that after more than forty years the scenario is not as bad as in the
past, but still today there are bottlenecks to be overcome for the
consolidation of biodigestion as an alternative for the generation of energy.
For
Palhares (2008) are some of the challenges in the application of biodigestion
in Agroindustrial scale:
•
Cultural: The process of anaerobic
biodigestion for swine extract is efficient; Research can be carried out to
increase this efficiency; however, the biodigestion process, by itself, does
not solve the environmental problems of swine farming; And which are not the
only available technology; That before proposing the technology, there should
be a feasibility study.
• Professional Training: There is still
a shortage of training for the operation of biodigesters, for technicians and
producers, in order to enable the correct use of these and to ensure
efficiency.
Professional
training is directly related to the management and efficiency of the process.
An organic matter may have a potential for generation, but it does not mean
that it will be generated with this potential; it depends on some factors, like
the correct handling and operation.
•
Public policy-making: For Sant'ana (2013) it is the
government's job to create favorable conditions for the improvement of energy
efficiency in industry, either through policies, programs or promotion actions.
For Palhares (2008) actions the provision to the environmental agencies of the
states, with all the information necessary for them to know the technology,
with its advantages and disadvantages, in order to assist in the environmental
licensing processes of the properties; Regulation of the use of biofertilizers
as fertilizer, throughnutrient management; Implementation of projects aimed at
producing energy from swine and other animal waste, with the construction of
plants in regions of animal concentration.
Barreira
(2011) lists two more challenges to be overcome in the use of biodigesters:
•
Maintenance of biodigesters: Proper
operation of a biodigestor depends on good maintenance. Potential leaks or
clogs in the gas outlet pipes and hoses may cause internal pressure changes in
the digesters, increasing the risk of explosions. In addition, oxygen may be
introduced into the system, inhibiting and retarding methanogenic activity.
• Control of the process: Among the variables can be controlled the
values of biomass temperature, amount of gas generated, pH, dwell time, among
others.
The function of
process control is to monitor and detect possible instability and establish
actions to eliminate or mitigate them. Ideally, it should be online, automated
and robust, detecting the first signs of instability in the process.
The following table
presents some parameters that can be monitored in the anaerobic digestion
process:
Table 8: Monitoring parameters in anaerobic
digestion
Source: Adapted from
Barichello (2011)
According to Bohrz (2010) the monitoring and control of the biodigestion process allows the optimization of the efficiency of the system. When these factors are properly monitored, they can contribute to the optimization of bacterial activity, thus increasing methane production.
There
is no doubt that the German technology used in the production and operation of
biodigesters is recognized as the cutting edge, giving the environment where
biodigestion is taking place, the necessary conditions for it to occur in the
most efficient way possible.
• Transportation and storage: Another important challenge to be
overcome in the production of energy through the biodigestion process is the
transportation and storage of biomass. The disposal of animal waste has,
lately, been one of the major
Creators and specialists, as well as for the bidding process as it involves
technical, sanitary and economic aspects.
According
to BRIDGWATER (2011), in animal confinement systems because biomass is a
dispersed resource, it has to be harvested, collected and transported to the
conversion facility. If the conversion facility is far from the point of
biomass collection and storage, such as biomass density, it may be so low,
transportation costs will be high, and the number of vehicles moved for
large-scale processing will be very high, And with consequent environmental
impact.
5. CONCLUSION
The analysis of the challenges to
the application of biodigestion on an industrial scale from strains of bovine
animals allows some conclusions:
The first is that there
is no single technology to solve the environmental problems of swine farming.
From biomass production conditions, social, environmental and cultural
conditions, one must propose the best technology.
The
consensus on which technologies to treat swine manure are more adequate and how
to control the pollution of these creations will not exist, as there are
technologies more suitable for each productive characteristic.
The second is that no solution
should be based solely on the economic, for example, with the objective of
selling carbon credits, because it will not perpetuate and will not solve the
environmental issue.
Currently, the challenges to be
overcome for the diffusion of biodigestors technology in Brazil in the
agroindustry stem from cultural issues, professional training, public
policymaking, maintenance, process control, transportation and storage.
The
elimination or at least mitigation of these factors, allowing the use of
biogas, as well as the use of biofertilizer in the swine properties, will add
value to the waste treatment process and reduce the costs of production, thus
allowing a holistic view under the Environmental management point of view.
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