1. Theses of Doctoral (PhD) dissertation
Optimizing the Agricultural and Food Industrial Biogas Production
Lili Mézes
Advisors: Dr. Tibor Bíró, Prof. Dr. János Tamás
UNIVERSITY OF DEBRECEN,
Kerpely Kálmán Doctoral School
Debrecen, 2011

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1. PRELIMINARIES AND OBJECTIVES OF THE DOCTORAL THESIS
As the depletion of fossil energy resources are drawing near, besides other alternative
technologies, the utilization of biomass is gaining ground dynamically (Láng et al., 1985).
The annual energy demand of Hungary is approximately 1040 PJ, of which 60-70% is
imported (Nagy, 2008; Láng et al., 1985). In 2007 the biogas production was represented with
only 0,8% in the overall energy production of the country (Dióssy, 2007). According to
Kovács and Kovács (2007) Hungary is ranked last among the members of the European
Union by the per capita biogas production index. There are just a few biogas plants in the
country; most of them are based on sewage sludge, accompanied by a couple of plants
running on agricultural by-product and waste, while the production of landfill gas is almost
irrelevant. Currently there are 10 biogas plants in operation throughout the country (Somosné,
2010), and there are also another 20 biogas projects of industrial scale on different level of
progress. The current study is based on the examination of the Regional Biogas Plant of
Nyírbátor (BP), which is the very first and most significant facility in Hungary.
The regulation of storage and land application of the large quantity production slurry
originated from concentrated livestock has been changed according to the Council Directive
91/676/EEC concerning the protection of waters against pollution caused by nitrates from
agricultural sources. Due to the fact that manure is utilizable on tillage only in a certain
proportion of the year farms are obligated to build isolated storage tanks. However a few
facilities have chosen to establish biogas plants instead, which is an option that requires a
major investment but in the long run it also can be an economical and cost efficient solution.
The regulation for processing animal waste has been tightened in order to decrease the hazard
of contamination and pathogens enter the feed chain through feeding stuffs (1774/2002/EC,
71/2003 FVM). The regulation classifies animal waste and by-product into three categories.
The first and second categories involve slaughterhouse wastes that have to be disinfected
before utilization. The third category contains animal waste of less risk to the environment
therefore disinfection is unnecessary, such as the mass quantity of feather produced by poultry
slaughterhouses.
My research focuses on developing special biogas raw material variants that result in higher
methane-yield during utilization. I examine the recycling of the large amount of slurry,
disinfected slaughterhouse waste and other animal waste produced by the BP. I elaborate a
solution for the degradation of the uneasily hydrolysable broiler feather followed by the co-

3. 3
fermentation method of pre-treated feather and pig slurry. I set up a database containing the
quality and quantity indicators of the applied raw materials and the fermentation end-product
in BP. I analyze the biogas production practice based on long term plant data and recommend
solutions for further development.
Detailed research topic of Doctoral Dissertation:
- I define the requirements of pre-treatment of feather produced by poultry
slaughterhouses.
- I examine the efficiency of biogas production from pig slurry in laboratory and pilot
conditions.
- I analyze the co-fermentation of pig slurry and pre-treated poultry feather in laboratory
environment.
- I determine the optimal mixing ratio of the pre-treated feather in the raw material
mixture depending on the toxic hydrogen-sulphide concentration.
- I study the relationship between the quality and quantity of raw materials and
fermenting end-products of BP, accordingly set up a material balance
- I rate the effects of years, seasons, raw material variants and random errors in the
biogas production process.
2. RESEARCH METHODS
Structural Scheme of research based on biogas production process:
Pre-treating of raw materialsProduction of raw materials
Other organic material basis
Crop-farming 2.3. BP
Stock-raising 2.3. BP
Laboratory 1.DU, BOKU
Stirrer 2.3. BP
Sterilizing Plant 2.1. CY
Equipment of heat-treatment 2.1. CY
Biogas 2.3. BP
Liquid end-product 2.3. BPUtilization of raw materials
Solid end-product 2.3. BP
Biogas Plant 2.3.BP
Plant scale experimental reactor 2.3. BP
Labor scale experimenatal reactor 1.DU
1. Figure. Research Scheme

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Notations of research locations:
1. Laboratory Experiments:
DU= University of Debrecen, Centre of Agricultural and Economy Sciences, Faculty of
Agronomy, Food and Environment Sciences, Institute of Water and Environmental
Management
BOKU= University of Natural Resources and Applied Life Sciences, Interuniversity of
Agricultural Biotechnology (IFA-Tulln)
2. Plant Experiments:
BP= Regional Biogas Plant of Nyírbátor
CY= Composting yard
Notations of Research objects:
1. Laboratory Experiments
1.1. Physical-biological pre-treatment of poultry feather for biogas production,
1.2. Physical-chemical pre-treatment of poultry feather for biogas production;
1.3. Fermentation of pig slurry;
1.4. Co-fermentation of pig slurry and pre-treated poultry feather
2. Plant Experiments
2.1. Plant scale pre-treatment of poultry feather
2.2. Plant scale fermentation of pig slurry
2.3. Biogas Plant: database build-up; examination of relationship between composition of raw
materials and biogas-yield; quality collation of raw materials and end-products
2.4. Utilization of pre-treated poultry feather in the biogas plant
2.1. Laboratory Experiments (DU) (BOKU)
2.1.1. Physical-biological pre-treatment of poultry feather for biogas production (DU)
The examination has been carried out of the degradability of poultry feather of slaughterhouse
origin by heat and micro-organism in the composting and anaerobic fermentation laboratory
of the department (DU). For the degradation of broiler feather was applied heat and KK1
strain of Bacillus licheniformis, a special bacteria dissolving keratin (Kovács et al., 2002;
Kovács et al., 2000).
Prior to the first experiment was determined the bacteria cell number by a Bürker chamber,
and also determined the extinction by a Filtherphotometer PF-10 in 605 nm realm (measuring

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accuracy: +/ − 10 nm). During the turbidimetric measurement of cell number the bacteria
culture was sampled hourly for two days. After that the calibration curve was prepared
according to the cell numbers germane to the extinction value. With the aid of the calibration
curve hereafter I was able to judge cell numbers and degradation rate by the extinction of the
bacteria culture. To inoculate the experimental settings were used bacteria culture with 1,5
extinction and 2,0*109
pce/cm3
cell number, then were persistently measuring the intensity of
refraction in the feather: water compound. On plant scale the feather: water mixture was
inoculated, - that had an extinction rate 4,94 - with bacteria culture of 1,55*108
pce/ml cell
number. The experimental adjustments were: heat treatment of 70, 100, 130°C, 1:1, 1:2, 1:3
feather: water ratio, 1, 3, 5% feather: bacteria culture.
According to the results of treatment series the most productive treatment was selected then
was tried to improve the efficiency of this combination with the comminution of feather. The
given feather quantity for 20, 30 and 40 seconds was comminuted, and then the comparative
length measurement of the original and the comminuted feather was executed. During the
experiment the following distinctive features of the samples: dry- and organic material
content, acidity and temperature were determined.
2.1.2. Physical and chemical pre-treatment of poultry feather (BOKU)
Examinations have been executed regarding the thermal and chemical pre-treatment, and
element content (C, N, S) of the poultry feather based on preliminary experimental results.
The feather was comminuted for 0, 40, 80 seconds by a special chopper (Kenwood, stainless
steel, volume of 1 liter). After that the length, width and thickness of the comminuted feather
(50 samples) were measured with a Merox digital vernier. The experimental adjustments
involved 70, 130, 160°C temperature, and 1:2 feather: distilled water/1% NaOH-solution
ratio. For the thermo-treatment of the poultry feather a microwave heat-treater (UltraClave)
has been used. For the examination of carbon, nitrogen and sulphur content, the solution
phase of the end-product has been prepared by a Beckman GS-6 type centrifuge on 2900 rpm
for 20 minutes. This step was followed by the inspection of the chemical oxygen demand at
1:5, 1:10 or in case of necessity even 1:20 dilution. For samples that have been homogenized
and heat-treated at 160°C, Syringe Filter Nylon (0,45 µm) has been used. For feather samples
interspersed with 1N NaOH-solution, homogenized and heat-treated at 130 and 160°C, 12
mm Sartorius filter and water spout pump were used. All the samples have been treated with
GS-15 type centrifuge at 12500 rpm for 30 minutes in Eppensdorf subsequently. ICP

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(ULTIMA) was used in order to determine sulphur content of the end-product’s pre-treated
solution phase. The method of pre-treatment described above was followed by a microwave
heat-treatment, paper filtering, dilution up to 45 ml and the addition of 5 ml HCl.
Pre-treatment of the original feather samples consisted of drying and homogenization prior
the carbon and nitrogen content examination, which was complemented by microwave heat-
treatment, filtering and was treated with HCl in case of sulphur. The carbon content
determination in the original feather sample heat-treating (Behrotest TRS 200) was used. The
chemical oxygen demand (COD) was defined by the addition of sulphuric acid then three
droplets of ferroin indicator followed by titration (665 Decimate, Titrant: 0,06 M ferrous
ammonium sulphate solution, titration until reaching red colour).
The amount of the organic matter that has dissolved into the end-product has been measured
by a spectrophotometer (DR 2800) after heat treatment (15 minutes, 150°C) (HT 2005) and a
KOI (1000-10000 ml/l) water analytics cuvette-test that has been supplemented with a water
analytics barcode. The total nitrogen-content has been determined with the Kjeldahl-method.
In case of the original method the measurement was executed after drying and homogenizing,
while in the liquid phase with the method described above. A piece of 1000 Kjeltab CT pill
was put into a glass tube, and was weighed by an analytic scale (Satorius Talent). 20 ml
sulphuric acid has been added (98%) and afterwards it went under a heat treatment about 4,5
hours (Gerhardt 40S, Kjeldaterm KB). The digestion equipment has a CPU on which the
digestion temperature can be adjusted (Max: 430°C, ±1%). The sulphur content of the original
poultry feather (dried and homogenized samples) and the liquid phase of the end-product
(microwave heat treated, digested with HCl and a filtrated on a jagged filter) has been
measured by an ICP. The absorption rate of the liquid phase of the end-product was
determined on 605 nm by a photometer (Perkin Elemer Lambda Spektrometer, +/-0,1 nm).
2.1.3. Fermentation of pig slurry (DU)
The recipe studies were conducted in a thermo-isolated box (4 pieces), where 4 stainless steel
containers – 6 litres each – were the fermentation media. The experiment was conducted
under normal air pressure and anaerobic circumstances. In order to partially remove possible
organic acid-compounds from the output gas washer bottles filled with distilled water were
used. Afterwards the gas was condensed with cooling equipment. The composition of the gas
mixture was determined with a Fisher-Rosemount NGA 2000 (CH4, CO2, O2) gas-analyser.
The hydrogen sulphide and ammonia (H2S, NH3) compounds were measured with a gas-

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analyser MX42A. Fermentation residue liquid from the biogas plant was used as inoculation
substance. The experiments were carried out under mezophilic (35°C) and thermophilic
(52°C) conditions. The dry matter content and the pH were determined (WTW 340i, +/-0,005)
in case of the raw material and the end-product as well. The carbon- and nitrogen-content
have been analysed in the central laboratory of the Bátortrade Ltd. by an Elementar VARIO
EL®
universal analyser equipment (MSZ 6830-4:1981), while the sulphur-content was
measured at the Instrument Centre of the University of Debrecen, Centre of Agricultural and
Economical Sciences, Faculty of Agronomy and Food and Environmental Sciences by an
Elementar VARIO EL®
analyser, that is described in the following website: www.aktivit.hu.
2.1.4. Co-fermentation of pig slurry and pre-treated poultry feather (DU)
The experiments were carried out as described in chapter 1.3. Following treatments were set
up: pig slurry and 5, 10, 20, 40% pre-treated poultry feather under mesophilic (38°C) and
termophilic (52°C) circumstances.
2.2. Plant Experiments
2.2.1. Pre-treatment of poultry feather on an industrial level (CY)
The site where the poultry feather – from slaughter – has been pre-treated on an industrial
level was the building at the composting site, which is owned by the Bátortrade Ltd. and
placed near to the biogas plant. The experiments were set up in a closed tank (type Tycoon)
that can be heated and is equipped with an internal mixing unit and aerating device, that has
double walls and that was originally planned for the sterilization of slaughter wastes. The used
treatment parameters were: 70 and 130°C; 1:3 feather: water rate; 1 and 3% feather: bacteria
culture. The pH and the temperature of the samples were measured at the site and in the
laboratory of the Bátortrade Ltd. with portable equipment WTW Multi 330i. The extinction
was measured by a PF-10 Photometer at 605 nm, while the cells were counted using an Alpha
BIO-3CCD microscope as described in chapter 1.1.
2.2.2. Industrial level fermentation of pig slurry
The mono-recipe fermentation of pig slurry was executed with Batch-process in a 10 m3
coat-
heated, acid-proof plastic inlay, up to 5 bar pressure proof tank. The input and – if necessary –
output of the pig slurry was performed by a pump. The required temperature was reached and

8. 8
ensured by using a heater and a thermostat. The mixture was performed in a hydraulic way by
a pump. The number of mixing measurements, just as their duration was automatic. The
produced gas was lead into a 50 l large, standing, pebble bed absorption tower that ensured
the partial remove of H2S and NH3.
2.1.3. Assessment of the Agricultural Biogas Plant (BP)
The biogas plant was established by BátorTrade Ltd. in 2002. The regional plant forms a
multi-role system, which besides carrying out conventional agricultural activities is also
producing biogas of high methane content (Bíró et al.; 2008; Mézes, 2008). The biogas is
produced in low Fermentors optimized for mixed combination of raw materials, and then it is
consumed in gas engines in order to generate both electricity and heat energy. The sheer
magnitude and the advanced technologies applied make the Regional Biogas Plant of
Nyírbátor (BP) a unique and cutting edge project in the world. The available capacity involves
17.000 m3
of Fermentor volume, 2600 kW electric energy output, a daily yield of 20– 25.000
m3
biogas and 110 000 tons of raw material consumption. As the plant is consuming mixed
materials, the 6 mesophilic – and 6 thermophilic Fermentors are operated in linked sequence
(Petis, 2008). The installation of an additional Fermentor-pair is currently in progress.
From the pressurized gas chamber of the Fermentor the biogas gets to the gas-cleaner, then
into the gasbag through a pipe system. The quality and quantity of biogas is being monitored
continuously throughout the process. Quality is being checked by a computer controlled gas-
analyzator (Chemec, B20) in mezo- and thermophilic fermentors alike. After anaerobic
fermentation the residual liquid is isolated. Solid and liquid phases are stored separately and
utilized to nutrient supply on farmlands.
Building up the database:
The overall amount/quantity of raw materials fed in the Fermentors consists of materials from
the two mixers (3 mixtures per day) and directly implemented materials. After recording the
data I have amassed/composed the daily 3 feed-ins with the appropriate quality indicators and
analysed the alteration in the given period (823 days interval).
Analysis of the amount and quality of the biogas produced:
Biogas production was calculated according to the gasflow meter of meso- and thermophilic
Fermentors to figure the overall daily gas yield in Nm3
.

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Connection between gas quantity and residence times:
The average residence time can be calculated from the maximal volume of Fermentors
(Vr)(m3
) and the amount of daily fed materials as HTI = Vr/V. This interval indicates the
degradability of the given substance, and the time needed for gas production to (be)
commenced.
Comprising weighted quality indicators of utilized raw materials and fermented end-
products:
A weighted value should be calculated for mixers and Fermentors based on the quality
indicators of the different raw materials. Thus we receive the quality value of the daily fed
variants depending on quantity (expressed in % connected to solid content), which is used to
figure the tons/day value. The correlation between the quality parameters of the utilized raw
materials and controlled the fermented end-product also has been analysed.
Correlation between the weighted quality parameters of input materials and the amount of
biogas produced:
My hypothesis was that the quality of raw materials (C, N, C/N, dry-, organic material cont.)
has an impact on the biogas production. The quantity parameters weighted by the daily
qualities were compared against the biogas yields in relation with the given residence times.
Developing variants depending on raw material availability in order to increase biogas
production:
Due to that some of the raw materials of the biogas production are only obtainable and
consumable seasonally, developing a set of different raw material variants for every specific
period is necessary.
With continuous quality control extreme values of severe system disadvantage can be filtered.
The applied theoretic model has originally been created by Kontur et al. (1993) to study the
completely different phenomena of groundwater regime, and later was adopted as a
mathematical analogy by Tamás et al. (2007) for their studies regarding biomass growth rate.
The model includes linear trend, periodic-, autoregressive- and random components which
have been collated properly executing forward transformation. Selecting the components I
could determine the annual discrepancy, seasonal deviation, biogas production periodicity,
recurring and cyclic in-house errors in technical discipline resulting in decrease of production,

10. 10
as well as the uncertainty factor of the model. The latter not only reflects random errors but
also refers to the technical reserves of the plant. The components of the timeline were defined
consecutively and separated in sequence from the remainder data conglomeration using the
following formula:
Yi=Ti + Pi + Ai + Vi
Ti=trend; Pi=periodic; Ai=autoregressive; Vi=variable component
2.2.1. In-plan utilization of pre-treated poultry feather
Bacterially pre-treated poultry feather was put into the F6, one of the 6 mezo- and
thermophilic Fermentor pairs. The feather of liquid consistence was implemented directly in
the mezofilic Fermentor. Based on the previous laboratory results pre-treated feather formed
5% of the raw material mixture implemented in the mesophilic Fermentor. Later the ratio of
the feather has been decreased to 2 and 1%. I have compared the gas yield and quality
indicators of the original variant used in the plant to the mixture completed with pre-treated
feather.
2.3. Statistical analysis
The data have been evaluated and analyzed with the computer programmes MS Excel and
SPSS 17 statistical programme. In order to test the normal distribution of the data was used
Kolmogorov-Smirnov test. For the simultaneous comparison of the mean values was used
analysis of variance. The relationships between the total N- (N g l-1
), carbon- (C g l-1
),
sulphur-content (S g l-1
), pH of the physically and chemically pre-treated poultry feather
liquid and the chopping duration (t sec.), just as the temperature (T °C) in the treatments with
“aqua dist.” and NaOH. In case of the results of the extinction and pH-value of the physically
and microbiologically pre-treated poultry feather under industrial conditions independent
sample T-test and linear regression analysis were applied. For the evaluation of the variances
of the methane-concentrations measured at the co-fermentation of pig slurry and pre-treated
poultry feather, just as for the simultaneous comparison of the means in case of the different
temperature treatments (mesophilic and thermophilic) the independent sample T-test were
used, as well. In case of the Regional Biogas Plant in Nyírbátor the quality parameters of the
raw-materials were described with explorative statistics (Explore), whereas the five highest
and the five lowest values were collected in the Table ’Extreme Values’. The relationship
between the quality parameters of the raw-material and the biogas production, just as the

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quality of the fermented end-product were analysed by a regression analysis. This was
calculated from the content and the biogas production, just as in case of the fermented end-
product as well from cumulated values in function of the retention times (HRT = 43 days)
(except for the C/N ratio).
3. MAIN STATEMENTS OF THE THESIS
3.1. Laboratory Experiments
3.1.1. Physical-biological pre-treatment of poultry feather for biogas production (DU)
The 1:1 ratio feather-water mixture was inappropriate for mechanical stirring. The 1:2 and 1:3
mixtures proved to be adequate for the same purpose. Due to the closed technology applied in
industrial circumstances it is strongly suggested to ensure compressed oxygen feed. In case of
using a ratio of feather: 5% bacterium culture the pH value showed a significant decrease.
Parallel to that, the amount of phosphate-buffer, used for pH setting increased having a
negative impact on cost efficiency. No significant differences were detectable between the
biodegradability of the mixtures with feather: 1% and 3% bacterium ratios, therefore on
industrial scale the using of the 1% ratio with a more favourable cost and material efficiency
is suggested. Therefore, the effect of pre-treating with the Bacillus licheniformis KK1 species
decreased the pH of the setting-variants, often was slightly acidified the solution, the control
treatments were slightly basic. In case of industrial conditions this problem can be more
significant. This problem might occur on a higher level; therefore by this biogas plants
suggested the utilization of milk of lime. It is natural and environmental-friendly material and
cheaper solution to balancing the optimal pH.
The treatments at 100°C about the Duncan-test were excluded, because the data weren’t
normal distribution. The following treatments resulted in significant differences from the
other treatments: 70°C, 1:2 feather: water ratio, 1, 3% bacteria culture, 1:3 feather: water
ratio, 1,3 % bacteria culture, 130°C, 1:3 feather: water ratio, 1% bacteria culture. The average
extinction value of these treatments was higher. The degradability of poultry feather was more
efficient. The control treatments (70, 100°C) showed significant different (P=0,05) from the
other treatments in case of extinction values, too. Under the experiment results all of the heat
treatment (70, 100, 130°C) can be used in practise, but the treatment at 70°C, because of the

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higher extinction values and economical-efficient is suggested. For industrial processing a
combination with a minimal heat-treatment and bacteria culture need is suggested.
3.1.2. Physical-chemical pre-treatment of poultry feather for biogas production (BOKU)
Treatments adjusted with water had had an average starting pH of 7,2, which has been
decreased minimally as a result of pre-treatment. In case of using 1% NaOH-solution the
starting average of 7,8 pH has increased with a unit. We can conclude, that the amount of
organic matter dissolved from feather (g KOI l-1
) while using distilled water and 0 sec
comminution has been doubled and quintuple at 130 and 160°C temperatures compared to the
samples pre-treated at 70°C. Using non comminuted feather adjusted by 1% NaOH-solution
and heat-treatment at 160°C provided the maximal value. Heat-treatment resulted in
significant increase of the solution's organic matter content (KOI), while homogenization had
no such impact. It can be said that the intensity of heat-treatment had a major influence on the
quantity of Nitrogen dissolved into the solution. When using distilled water, heat-treatment
caused an N increase of 50% (1,5 times) at 130°C, and 250% (3,5 times) at 160°C compared
to the results achieved with non comminuted samples heat-treated at 70°C. When using 1%
NaOH-solution, heat-treatment realized an N increase of quadruple at 130°C, and quintuple at
160°C. The effect of the homogenization have been changed this value slightly and inversely
proportionally. Using non comminuted feather adjusted by 1% NaOH-solution and heat-
treatment at 160°C provided the N-content of the solution-phase the maximal value. From the
poultry feather into the solution dissolved N-content reached the maximal value in case of the
treatment which was non-homogenized, at 160°C heat-treated and chemically-treated. In case
of using distilled water, homogenisation for 40 sec and heat-treatment at 160°C can be
realized. The resulting correlation coefficients (R) and their significance values (P) indicated
that while homogenization has been ineffective, temperature has influenced all three
parameters. The average C/N ratio of the end-product by using distilled water was 6,9:1, and
by NaOH-solution 11,4:1.
3.1.3. Fermentation of pig slurry (DU)
After the comparison the treatments with and without inoculation material we have revealed
that the inoculation material has only a slight increasing effect on the methane production. But
a significant difference could be observed in the time until the maximal concentration had
been reached: in case of the untreated samples the hydraulic retention time was 31 days, while

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this was only 23-25 days in case of the inoculated samples. Regarding the one-week sum of
the produced biogas amounts it can be stated that maximal production values (5,46 dm3
day-1
)
were reached in case of the inoculated thermophilic treatments. The production rates were
stable from the second until the fourth week. As the effect of the inoculation the hydraulic
retention time, just as the dry- and organic matter content of the end-product showed a more
decreasing tendency as in case of untreated samples. The production of the inhibiting
effecting NH3 and H2S was moderate in the experiment.
3.1.3. Co-fermentation of pig slurry and pre-treated poultry feather (DU)
Upon the results of the experiments it can be stated that the mixture rate of the raw material
that contains both pig slurry and poultry feather determines the biogas production
significantly. Under mesophilic conditions the mixture rates of 5 and 10% resulted in a
favourable production, the amount of the produced biogas (dm3
day-1
) exceeded the values of
the production at mixture rates of 20 and 40% by far (50%). In case of thermophilic
fermentation the process took less time (5-6 days) and a slight increase (1-2%) of the
produced biogas could be observed as well.
The biogas quality in case of the poultry feather mixture rate of 5 and 10% showed better
results and differed significantly from the rates of 20 and 40%. In case of treatments with a
feather mixture rate of 5 and 10% methane concentrations around 60% stayed stabile.
Regarding their trends and values they were similar to the mesophilic reference
measurements, but in case of the thermophilic treatments these treatments differed
significantly from the control treatments in both phases. There was no difference between the
methane concentration of the thermophilic co-fermented slurry and 20 and 40% feather, but
they differed significantly from other treatments. Comparing the mesophilic and thermophilic
fermentation it can be stated that as an effect of the higher temperature the process was started
faster and from the aspect of the methane concentrations was more constant.
The amount of H2S – that has a corrosive effect and causes bad smell – was significantly
increased in case of a feather mixture rate of more than 10% (20 and 40%) at the beginning of
the fermentation and it affected the methane production negatively, the quality of the
produced biogas was worse. In case of the mixture rates of 5 and 10% the hydrogen sulphide
concentrations of the produced biogas – in contrast to the higher mixture rates – were more
favourable and showed a significant difference in the first phase of the production. The same
tendency could be observed in case of the thermophilic fermentation, but the extent of the

14. 14
H2S-production showed a slight increasing tendency (1%) in contrast to the mesophilic
treatments and the production of the hydrogen sulphide reached its maximal value already on
the 9th
day in case of the 5% treatment, while in case of the 10% treatment on the 11th
day.
Regarding the ammonia content of the biogas it can be stated that the produced amount was
significantly high in the first stage (ppm) because the most of the easily degradable nitrogen.
After that this value decreased as the not so easily degradable forms were degraded. This
process was more balanced. In the first stage of the ammonia production a significant
difference could be revealed between the following groups: mesophilic 5% and thermophilic
20%, and reverse thermophilic 5% and mesophilic 20% treatments, just as mesophilic 10%
and thermophilic 40% and reverse thermophilic 10% and mesophilic 40%. In the much more
balanced ammonia-producing final stage three groups could be differed: mesophilic 20 and
40% just as thermophilic 5% treatment build the first, thermophilic 10% was the second,
while the mesophilic 10%, the thermophilic 20 and 40% treatments were the third group.
These treatments showed a significant difference. According to the experimental experiences
it’s recommended to maximize the rate of the mixed pre-treated feather in 5% in the biomass.
The production of the increased inhibiting substance can be avoided so. It was also stated that
the reduced gas-production was caused by not only the produced H2S, but the closer C/N ratio
that was caused by the high protein content of the feather.
The fermented by-product of the biogas production has several favourable parameters in
contrast to other organic and mineral fertilizers. The produced “bio-fertilizer” has significant
N-, P-, S-, and micro-element content; that enables us to implement an environment-friendly
nutrient-supply. Due to its higher sulphur-content the fermentation liquid of a biogas plant
that uses keratin-containing material can result a more expressed yield increment on sulphur
deficient soils. The co-fermentation of slurry and poultry feather gives not only a utilization
alternative of the placement problems of the slurry – according to the nitrate-directive and the
IPCC - , but a solution possibility of the placement of poultry feather that cannot be used any
more as fodder.
3.2. Plant Experiments
3.2.1. Plant scale pre-treatment of poultry feather (CT)
The reflectance of experience “A” (1%,1:3) – heat-treated on 70 °C - increased intensively in
the beginning of the fermentation process (2,0-7,8) and reached the maximum extinction on

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day 4 at 13,4. The extinction in the case when we used 130°C heat-treatment, 1% and 3%
inoculums increased sharply, reached its maximum on day 6 at 12,2. The trend of experience
“B” – set with 70°C heat-treatment and 3% inoculums – did not differ significantly. The
increase of the inoculums did not cause a commensurable growth of the effectiveness of the
degradation. In the case of experience “C” and “D” - heat-treated on 130°C – there was no
significant difference in the effectiveness of the degradation. The results do not indicate the
utilization of the less cost-effective 130°C heat-treatment and the larger concentration of
inoculums. The optimal time of the treatment is 5 and half days. The strongest coherence
between the measured pH and extinction appeared when we used regression analysis with
quadratic function in the cases of 70 and 130°C heat-treatments. Based on the independent
sample T-test we can conclude the treatment is optimal when the extinction is larger and the
pH is close to neutral. According to this the 70°C treatment was more effective than the
130°C. There was a great difference between the quality parameters of the original poultry
feather – directly from the slaughter-house – and the parameters of the heat-tread one. Thanks
to the treatments its N-content decreased to 54,5%, C-content to 38,7%, S-content to 31,28.
The decrease of the sulphur-content proves the degradation of the disulphide-bridges – the
keratin – which means the easier hydrolysis of the poultry feather. In plant-scale the too large
amount of the animal protein may cause problems. The produced hydrogen sulphide abates
the quality of biogas and may damage the equipments of the fermentation tank and the gas-
engines because the corrosive effect. By this, it is very important to take the available raw
materials into consideration when we determine the maximum amount of the poultry feather
adapted to the actual biogas plant.
3.2.2. Plant-scale degradation of pig liquid manure
The experiments in the concrete fermentation tank (10 m3
) which was under pressure were
unsuccessful, so tanks under pressure are not suggested for plant-scale use. For effective
biogas production 37°C and no pressure was optimal. According to the produced biogas
(11m3
/day) the special fermentation tank is suggested for the degradation of pig liquid manure
(when only liquid manure is used in the recipe). The production of the harmful gases
decreased during the degradation process because larger amount of proteins containing
nitrogen and sulphur was only available in the beginning of the procedure. The income is
“saved” price of natural gas saved by the utilization of the biogas. The liquid manure as a
waste is a cost factor for the animal farms – deposition and utilization costs. Instead of

16. 16
building liquid manure storage - as it is determined in the Nitrate-directive – building a biogas
plant might be a more attractive alternative for the farms. In the 10 m3
fermentation tank
during effective degradation and optimal 28 days cycle with discontinuous running the
produced biogas is about 200 m3
, while, when the running is continuous, the raw material
added daily and the 28 days cycle is ensured, the produced gas is about 290 m3
. That means
3780 m3
/year. From this 750 m3
is used for heating the tank. The more 3030 m3
biogas is
equal with 1720 m3
natural gas, which means a considerable income for the farms at these
days when just only one fermentation tank is used. The calorific value of the produced biogas
is averagely 19,3 MJ/kg.
3.2.3. Assessment of the Agricultural Biogas Plant (BP) /Analysis of a biogas plant based on
raw materials from agriculture (BP)
Database build-up:
During the examined time period the amount of cattle liquid manure rose to 32.000 m3
from
20.000 m3
because of the change of the technology. The amount of used poultry wastewater
continuously decreased from 8.000 to 5.000 m3
. The amount of the plant raw materials
changed seasonally. The freshly cut green materials – that increase the C-content, so the gas-
production sharply – were only available during the vegetation period, while the silage -
because of the storage – is available all year. The missing amount of the silage from 2008 was
ensured by other plant raw materials, so the list of the used materials broadened: green peas,
E. triticale, sugar-beet, cheese-whey, grass-cutting, Lucerne, sugar-beet-cutting and corn.
Next to this, the recirculation of the fermented final product – especially the separated solid
phase – between November and May increased in both years, but in 2008 the used amount
also increased. The N-content of the cattle liquid manure was well-balanced (3,1%), the C-
content was averagely 40,3±2,4%, so the C/N ration was between 12 and 16. The dry material
content was 4%, the organic material content was averagely 1% while the pH was about
neutral. The daily change of the cattle liquid manure was considerable during the summer
period in 2007. Its C/N ratio was about 19,1, dry material content was 21,2% and organic
material content was 2,7%. The C/N ratio of the silage was about 27,6, the dry material
content was 26,1 and the organic material content was 2,8%. The average value of the C-
content was 45,8%. The load of the agitator, so the quality of the raw material, was mainly
determined by cattle manure, the silage and the grained maize. Next to the materials of the

17. 17
agitators, liquid manure, poultry wastewater, milk-whey, separated material, sterilized liquid
slaughter wastewater (class 2 and 3), gravy and glycerine (by-product of bioethanol
production) were uploaded directly to the digesters. After the proportion of the agitators
(85,7%) the rate of the uploaded gravy was the largest (11,2%). The average amount of the
uploaded poultry wastewater and separated material was 1,5%. Consider this yearly; in 2006-
2007 the poultry wastewater was deterministic, while in 2008 the separated material and the
liquid manure had greater importance. The raw material base of the agitators was 8770
m3
/month, while the base of the digesters was 1456m3
/month. The amount of the loaded
materials to the agitators was very various (SD=±1165 m3
), while it was lower in the case of
the digesters (SD=±325 m3
).
Quality and quantity analysis of the biogas production:
The amount of the monthly produced gas was between 430.000 and 920.000 Nm3
, while the
daily biogas varied between 14.657 and 21.968 Nm3
. The daily average of the produced gas
was 18.570 Nm3
comparing the two types of the digesters the produced gas in the mezophilic
digesters was averagely larger by 43%. In January the trend was different, the process was the
opposite. The amount of the total produced gas also increased comparing with the other
months. That time, the amount of the used technological wastewater, silage and sugar-beet
cutting was increased in the recipe. The average value of the methane-content was 58,7%, but
the maximal 74% indicates that a great potential is available, which can be achieved by a
well-balanced, less various recipe of the used raw materials. The mixture should be adapted to
the season. The hydrogen-sulphide content of the biogas after the sulphide –remove was
averagely 201 ppm, meanwhile the ammonia was 39 ppm. Because of the high values a new
sulphide removal technology is advised – adopted to this biogas plant - , the effectiveness of
the actual technology cannot be improved. In winter time the C/N ratio is lover because of the
continuously available, sterilized slaughter waste.
Connection between the produced gas and the hydraulic retention time:
Examining the data of the hydraulic retention time and the 43 day sum of the produced biogas
we can build up a quadratic function (y=-0,6067x2
+ 2173,5x - 1E+06) with medium
dependability (R=0,53). The medium dependability evinces the hypothesis, that the hydraulic
retention time affects the amount of the produced biogas.

18. 18
Coherences between the used materials and the fermented final product:
The coherences between the base of raw materials and the quality parameters of the fermented
final product can only be analysed if the hydraulic retention time is accurately determined. In
the case of the mesophilic fermentation tanks this is averagely 19 days, while in the
thermophilic tanks is about 23 days. The total hydraulic retention time (HTI) was averagely
43 days. To reduce the HTI the use of more easily-degradable raw material is advised. There
was no significance difference between the cumulative and measured values of the raw
materials. Except the C/N ratio was strong coherences with power function. The N-content
and the dry material content of the raw materials and the fermented final product showed the
strongest coherences.
Coherences between the quality parameters of the raw materials and the amount of produced
biogas:
My hypothesis was the quality parameters of the raw materials (C, N, C/N, dmc., omc.)
affects the biogas production. The determination coefficient of the quadratic polynomial
functions was between 0,7 an 0,8, so there were strong coherences. In the case of C/N ratio
and biogas production power function can be used with medium dependability (R=0,62).
The specific optimal values (1 ton) were determined to the quality parameters. So, the
methane production when the N-content was 1 t was 12.192 Nm3
/day, when the C-content
was 1 t was 1019 Nm3
/day. The largest values of biogas production (20.492-22.040 Nm3
/day)
are linked to 10:1 and 11.4:1 C/N ratios. 378-488 Nm3
/day can be connected to 1 t dry
material content. 1 tone organic mater content results approximately 1673-2086 Nm3
/day
methane production.
Comparison of different variables related to availability of raw materials to produce more
biogas:
The model parameters of the time series were determined after each other and separated from
the database. A linear function can be joint the data of biogas production with 51% medium
dependability. During the examined 823 days time period the gas production rose by 6,08
Nm3
daily. The numerical solution of the equation is the following: Ti= 15706,51 + 6,077i.
Assuming there is seasonality in the raw material base. The value of the n a*cos(2π*i/90)
periodic coefficient was -195,35, while the value of the b*sin(2 π i*i/90) periodic coefficient
was 122,36 Nm3
. The value of Pi varied between 200 and 600 Nm3
, so the size of the change

19. 19
is about 400 Nm3
, thanks to the periodicity. The periodic effect affected the biogas production
with 2,31% in 2007, with 1,98% in 2008 and with 2,15% in the total examined time. The
technological discipline affected the biogas production with 3%, but the maximal value was
20%. The random error of gas production – if we consider the whole difference – can reach
31,6%. In this case the random error is an unpredictable technological error, human-factor, a
loss of biogas production caused by accidental toxic effect, or an unexplained increase of gas
production that can be determined as a technological reserve.
3.2.4. Utilization of pre-treated poultry feather in the biogas plant
The biogas production did not change significantly after the utilization of the poultry feather.
Because of the large keratin content of the poultry feather the biogas hydrogen-sulphide
content – this is anyway too high – largely increased. Recommendable maximize the amount
of poultry feather as 2% in the recipe of the given raw materials. With the increased mixing
rate of the poultry feather contains many proteins the possible amount of allocated fermented
final product decreased by degrees. For example, from the original 4473,7 kg/ha decreased to
3822,8 kg/ha if the rate of mixed poultry feather was 5%. Though, the fermentation product
containing sulphide may increase the yield on soils containing less sulphide.
4. NEW AND NOVEL SCIENTIFIC RESULTS OF THE THESIS
The new and novel scientific results of my thesis can be summarized as follows:
1. Thesis: The optimal hydrological retention time and the produced quantity of inhibitor type
gases for pig slurry fermentation and for co-fermentation of pig slurry and pre-treated poultry
feather were determined. Due to the amount of produced hydrogen sulphide (ppm) the critical
mixing ratio of feather proved to be 5-10% in laboratory environment and 2% in the given
biogas plant.
2. Thesis: The relationship between the used raw-material combinations in the agriculture
biogas plant and the end-product were revealed concerning the quality and quantity
parameters (C-, N-, organic matter and dry matter content, C/N rate). The relationship
between the produced biogas amount and the retention time was also analysed. Average
hydrological retention time (HRT) has been determined for mesophilic- (19 days) and
thermophilic (23 days) fermentors and for the whole system (43 days). The relationships were
significant.

20. 20
3. Thesis: Specific (1 ton input material) optimal effectiveness indicators and interval
optimum values have been elaborated in order to reach higher biogas production. The specific
indexes were: N: 12192 Nm3
/day, C: 1019 Nm3
/day; dry matter content: 373-488 Nm3
/day;
organic matter content: 1673-2086 Nm3
/day, optimal C/N ratio: in case of 10:1-11.4:1 20492-
22040 Nm3
/day. A strong relationship could be revealed between the quality parameters of
the raw material and the biogas production (Nm3
) (the sum of the data of 43 days).
4. Thesis: Based upon the analysis of the time series derived trend and periodic effects were
defined for the process of biogas production. The time series trend-analyses is applicable to
measure the fluctuation of the periodic biogas production (Pi=±400 Nm3
) and also to evaluate
the volume of a technological reserve (Max.=20%).
5. PRACTICAL USEFULNESS OF RESULTS
1: The optimal pre-treatment parameters for both laboratory and plant environment were
determined. 70°C temperature, 1:2 and 1:3 ratios of feather and water, 1% concentration of
bacteria culture, mechanical stirring are recommended at laboratory scale. 70°C
temperature, 1:3 ratio of feather-water, bacteria culture of 1% concentration, compressed
oxygen supply are recommended for industrial environment. I am providing data for the
technological realization of plant-scale pre-treatment of hardly hydrolysable secondary
poultry feather.
Structure of Tycoon steal tank: 6 m3
, double-walled, heated, with internal mixing- and
compressed air supply, computer-controlled pressure, temperature, compressor and
unloading.
Optimal mixing: 1:3 feather: water ratio
Hydraulic material transfer: oxygen-input in every 10 minutes with compressors, which
has a beneficial effect on the degradability and optimal homogeneity.
2: Measuring turbidity and extinction, and using turbidimetric method to evaluate the
degradation of poultry feather. Specific pre-treatment and microwave destruction of
poultry feather for C-, N-, and S- content determination.
Preparation of the solution phase of the end-product: The non-homogenized feather
solution, which was pre-treated at 70, 130, 160°C temperature, and the homogenized
feather, which was pre-treated at 70, 130 °C was centrifuged on 2900 rpm for 20 minutes.

21. 21
For samples that have been homogenized and heat-treated at 160°C 45 µm filter has been
also used. For feather samples interspersed with 1N NaOH-solution, homogenized and
heat-treated at 130 and 160°C, 12 mm filter and water spout pump were used. Furthermore
all the samples have been treated with centrifuge at 12500 rpm for 30 minutes
subsequently. This step was followed by the inspection of the chemical oxygen demand at
1:10 or in case of necessity even 1:20 dilution.
3: Technical parameters of construction of individual 10 m3
coat-heated, acid-proof plastic
inlay, up to 5 bar pressure proof tank with a heating-mantle, a thermostat, a hydraulic
mixing, 50 l large, standing, pebble bed absorption tower.
HRT 28 days; biogas yield: 11 m3
/day; Discontinuous operation: 200 m3
; Continuous
operation: 290 m3.
4: Statistical evaluation of the raw material base of regional biomass utilization: quality
parameters (26 input materials, 823 day (10.2006-12.2008)) and quantity parameters (C, N,
om., dm.-content, C/N ratio). Determination of the parameters biogas technology based on
heterogeneous raw materials: C/N ratio (13:1), HTI (43 days), quality (CH4: 59%, CO2:
29%, SH2: 275 ppm, NH3: 39 ppm) and quantity parameters (18570 Nm3
/day, 675000
Nm3
/month) of biogas.

22. 22
6. PUBLICATIONS IN THE SUBJECT MATTER OF THE THESIS
Bíró, T., Mézes, L., Hunyadi, G., Petis, M. 2008. Effects of biomass recipes on the output
liquid phase of biogas production. Cereal Research Communications. Supplement. 36. 5. pp.
2071-2074.
Dióssy L. 2007. Megújuló energia felhasználásának esélyei és lehetőségei, Kereskedelmi és
Iparkamara. 2007. Június 6. Sopron.
Gruber, W. 2007. Biogasanlagen in der Landwirtschaft. Aid infodienst. Verbraucherschultz,
Ernährung, Landwirtschaft e.V. Bonn. 1453.
Kontur I., Koris K., Winter J. 1993. Hidrológiai számítások. Akadémiai Kiadó. Budapest.
143-184.
K. L. Kovács, Z. Bagi, Cs. Bagyinka, L. Bodrossy, R. Csáki, B. Fodor, T. Hanczár, J. Tusz,
M. Kálmán, J. Klem, Á. Kovács, J. Lu, M. Magony, G. Maróti, K. Perei, B. Polyák, S.
Arvani, M. Takács, A. Tóth, G. Rákhely. 2000. Biohydrogen, biogas, bioremediation.
[Biohidrogén, Biogáz, Bioremediáció] Acta Biol. Debrecenica, 22. 47-54.
K. L. Kovács, Z. Bagi, R.-K. Perei, Gy. Csanádi, B. Fodor, Á. T. Kovács, G. Maróti, M.
Magony, B. Bálint, P. Valastyán, G. Rákhely. 2002. Biohydrogen, biogas, bioremediation.
Proc. "Power of Microbes in Industry and Environment" Conf., Opatija, Croatia, 7-9 June,
2002. p. 17.
Kovács L. K., Kovács A. 2007. A biogáztermelés hazai elterjesztésének lehetőségei és
korlátai. Ma & Holnap. VII. évf./2. 22-25.
Kovács A. 2007. III. Biogáz Konferencia. Az EU megújuló energia politikája: célkitűzések és
realitások. Budapest.
Láng, I., Hornos, Zs. Csete, L. Krolovánszky, U.P., Tőkés, O. 1985. A biomassza
felhasználása. Mezőgazdasági Kiadó. Budapest 10-11., 55-56.
Mézes, L., Bíró, T., Tamás, J. 2008. Results of biogas production experiments based on
agricultural and food industry wastes. Tamás J., Csép N.I., Jávor A. (szerk.) “Natural
resources and sustainable development.” Acta Agraria Debreceniensis. Supplement. pp.297-
303.
Nagy J. 2008. A biomassza-hasznosítás lehetőségei és képessége Magyarországon. Mag
Kutatás, Fejlesztés és Környezet. 2008.09-10. 40-44.

23. 23
Petis M. 2007. Biogázról a gyakorlatban. Bioenergia. Bioenergetikai Szaklap. Szekszárdi
Bioráma Kft. Szekszárd. II. évf. 2. 21-25. /www.dcc.uni-miskolc.hu/content/3/image003.jpg
Petis M. 2008. Biogáz hasznosítása. Energiapolitika 2000 Társulat. Energiapolitikai Hétfő
Esték. Budapest. 2008. február. 11.
Somosné Nagy A. (szerk.) 2010. A biogáz szerepe a vidékgazdaságban. „ A biogáz szerepe a
vidékgazdaságban” szakmai nap. 2010. április 29-30. Kecskemét.
Tamás J., Bíró T., Burai P. 2004. Mezőgazdasági állati eredetű veszélyes hulladékok biogáz
célú hasznosítása. XLVI. Georgikon Napok. Keszthely. 1-5. CD.
Tamás J., Bíró T., Szőllősi N. 2007. Analyze of biomass productivity by timeseries
remotesensing data in region Nyírlugos. In: Láng I., Lazányi J., Csép N. (Szerk.) 2007. Joint
International Conference on long-term Experiments, Agricultural Research and Natural
Resources. Univ. Debrecen Centr. Agric. Sci.. Univ. Oradea. Debrecen, Romania. 44-50.
1774/2002/EK Európai Parlamenti és Tanácsi rendelet a nem emberi fogyasztásra szánt állati
melléktermékekre vonatkozó egészségügyi előírások megállapításáról. Módosítva: Bizottság
2007/2006/EK rendelet.
71/2003. (VI. 27.) FVM rendelet az állati hulladékok kezelésének és a hasznosításukkal
készült termékek forgalomba hozatalának állat-egészségügyi szabályairól
49/2001. (IV. 3.) Korm. rendelet. Nitrát direktíva a vizek mezőgazdasági eredetű
mitrátszennyezéssel szembeni védelméről, mely a 91/676/EKG tanácsi irányelvét illeszti a
hazai jogrendszerbe. Módosítva: 27/2006. (II.7.), 81/2007 (IV.25.)

24. 24
7. LIST OF THE SCIENTIFIC COMMUNICATION PUBLISHED IN THE PROFESSIONAL OF
THE DISSERTATION
Scientific paper in foreign language, reviewed Hungarian journals:
- Bíró, T., Mézes, L., Tamás, J. (2007): The examination of poultry feather digestibility
for biogas production. Cereal Research Communications. 35. 2. ISSN: 0133-3720. pp. 269-
272. (IF: 1,19)
- Mézes, L., Bíró, T., Tamás, J. (2008): Results of biogas production experiments based
on agricultural and food industry wastes. Tamás J., Csép N.I., Jávor A. (szerk.) “Natural
resources and sustainable development.” Acta Agraria Debreceniensis. ISSN: 1588-8363.
pp.297-303.
- Bíró, T., Mézes, L., Hunyadi, G., Petis, M. (2008): Effects of biomass recipes on the
output liquid phase of biogas production. Cereal Research Communications. 36. 5. ISSN:
0133-3720. pp. 2071-2074. (IF: 1,19)
Scientific paper in a reviewed, Hungarian language journal:
- Mézes L., Bíró T., Tamás J., Petis M. (2007): Baromfi toll feltárhatóságának
vizsgálata biogáz célú hasznosításhoz. Acta Agraria Debreceniensis. 26. ISSN: 1587-
1282.113-118.
- Mézes L., Bíró T., Tamás J., Petis, M. (2007): Baromfi toll hőkezelése és mikrobiális
előkezelése biogáz célú hasznosításhoz. Acta Agraria Debreceniensis. 27. ISSN: 1587-1282.
215-219.
- Mézes L., Bíró T., Petis M., Tamás J. (2008): Keratin-tartalmú hulladékok üzemi
méretű biológiai előkezelése. Acta Agraria Debreceniensis. 30. ISSN:1587-1282. 59-65.
- Hunyadi G., Bíró T., Tamás J., Mézes L., Kosárkó, M. (2008): Rothasztott
szennyvíziszap felhasználásával kialakított komposztrecepturák tápanyagtartalmának
vizsgálata. Simon L. (szerk.). Talajvédelem. Különszám. ISSN: 1216-9560. 395-402.
- Mézes L., Bíró T., Petis M. (2009): A C/N arány és a biogáz hozamok
összefüggésének vizsgálata a Nyírbátori Biogáz Üzemben. Acta Agraria Debreceniensis. 35.
ISSN: 1216-9560. 63-68.
- Mézes L. (2010): A vágóhídról származó baromfi toll fizikai és kémiai kezelése. Acta
Agraria Debreceniensis. 42. ISSN: 1216-9560.51-56.

25. 25
Foreign language, reviewed conference proceedings:
- Mézes, L., Bíró, T., Juhász, Cs., Hunyadi, G. (2008): Innovative technology for biogas
production from pig slurry. Koutev, V. (ed.). 13th RAMIRAN International Conference.
„Potential for simple technology solutions in organic manure management”. ISBN: 978-954-
9067671-6-3. pp. 331-334.
- Mézes, L., Bíró, T., Hunyadi, G., Tamás, J., Petis, M. (2009): The poultry feather
digestility nad utilisation for biogas production. Kuntz, A. (ed.). I. International Symposium
on Animal Waste Management. Florianópolis, Santa Catarina State, Brazil. CD. Proceeding.
pp. 218-223.
- Kamarád, L., Mézes, L., Gabauer, W., Braun, R., Kirchmayr, R. (2009): Monitoring
and operating efficiency of biogas plants in Austria. Conference proceedings of International
Conference Construction and Operation of Biogas Plants. Třeboň, Czech Republic. 15.-16.
October. ISBN-978-80-254-5455-8. pp.43-47.
Hungarian language, reviewed conference proceedings:
- Bíró T., Mézes L., Petis M., Kovács L. K., Bagi Z., Hunyadi G. (2008): A baromfi
toll, mint biogáz alapanyag. Kiss T., Somogyvári M. (szerk.). Via Futuri 2007. A biomassza
alapú energiatermelés. BIOKOM Kft. Pécs. ISBN: 978-963-06-5993-2. 156-163.
Foreign language, not reviewed conference proceedings:
- Mézes, L., Bíró, T., Petis, M., Hunyadi, G. (2008): The practical coherences of biogas
production based on mixed compositions in South-Nyírség Region of Hungary. In: IV. World
Congress of Agronomists and professional in Agronomy. Madrid, Spanyolország, 2008.10.28-
2008.10.30. Madrid. pp. 152-156.
Hungarian language, reviewed conference proceedings:
- Mézes L., Thyll Sz., Bíró T. (2008): Kutatási eredmények a mezőgazdasági és
élelmiszeripari hulladékokra alapozott biogáz-előállítás terén. Tóth G. (szerk.). 50. Jubileumi.
Georgikon Napok, Keszthely. CD Kiadvány. ISBN: 978-963-9639-32-4. 7-12.
- Mézes L. (2011): Baromfi vágóhídi hulladékok mennyisége, a baromfi toll
hasznosításának lehetőségei. XVII. Ifjúsági Tudományos Fórum. Keszthely. CD Kiadvány.
ISBN: 978-963-9639-42-3.
- Bíró Gy., Mézes L., Nyírcsák M., Tamás J., Borbély J. (2011): Laboratóriumi anaerob
fermentációs rendszer irányítástechnikai fejlesztése. XVII. Ifjúsági Tudományos Fórum.
Keszthely. CD Kiadvány. ISBN: 978-963-9639-42-3.

26. 26
Hungarian language, reviewed conference presentation:
- Mézes L., Bíró T., Hunyadi G. (2007): Sertéstelepek biogáz-ellátásának egy
lehetséges technológiai alternatívája. Országos Környezetvédelmi Konferencia.
Tanulmánykötet. Balatonfüred. pp. 68-76.
- Mézes L. (2007): Baromfi toll feltárhatóságának vizsgálata biogáz célú
hasznosításhoz. IV. Jedlik Ányos Szakmai Napok. Absztrakt. Veszprém. 48.
Documentary publication:
- Bíró T., Mézes L., Petis M., Kovács L. K., Bagi Z., Hunyadi G., Tamás J. (2008): A
baromfi toll biogáz-alapanyagként történő hasznosítása. Pápa Á. (szerk.). Bioenergia.
Bioenergetikai szaklap. Szekszárdi Bioráma Kft. Szekszárd. 3. 1. ISSN: 1788-487X.18-21.