Alina REJMAN-BURZYŃSKA, Halina MAKSYMIAK-LACH, Eugeniusz JĘDRYSIK ?Central Mining Institute in Katowice
Please cite as: CHEMIK 2013, 67, 5, 446?453
Biogas is produced in the process of organic substance decomposition via methane fermentation and contains 50?75% of methane (CH4) and 25?50% of carbon dioxide (CO2) as well as small amounts of ammonia, hydrogen sulphide, hydrogen, mercaptans and other gases. Only biogas containing at least 40% of methane can be used to produce thermal or electric energy.
The main resources used to produce biogas on an industrial scale are organic waste, including wastewater residues, agricultural and food waste, animal manure and organic fractions of municipal waste. The amount and composition of biogas depend on the chemical composition of the resource fed to fermentation and on process parameters (reaction time, temperature). 1 kg of carbohydrates yields, on average, 0.42 m3 of CH4, of proteins ? 0.47 m3 of CH4, while of fats ? 0.75 m3 of CH4, but fats are characterised by a long decomposition time. The biogas calorific value depends on the content of methane and equals 17?25 MJ/m3 (1 m3 of biogas is an equivalent of energy in 0.93 m3 of natural gas or in 1.25 kg of coal).
Biogas production facilities are constructed closed to municipal waste landfills and in wastewater treatment plants as well as near farms and agricultural and food processing plants. Biogas can be used in several ways: it may be utilised to produce heat and electric energy or, after treatment, injected into the gas grid or used as vehicle fuel and in technological processes. It is particularly beneficial to use biogas to produce electric energy and heat in cogeneration systems (CHP ? Combined Heat and Power). Cogeneration energy management (CHP) allows for significant economic savings in comparison to producing heat in a conventional heat plant and electric energy ? in a condensing power plant. It results also in environmental benefits. Advantages from using biogas facilities are i.a. as follows:
? production of ?green energy?
? reducing the emission of greenhouse gases
? lowering the costs of waste storage
? preventing the pollution of soil, ground waters, surface reservoirs and rivers
? production an efficient natural fertiliser, easily absorbed by plants.
Biogas in Poland may become an important energy source which would increase the supply stability of gas fuels; it may also play a significant role in fulfilling our country?s obligations towards the European Union, which are included in EUROPE 2020 strategy. The ?20?20 till 2020? strategy assumes the reduction of greenhouse gas emission by 20% and achieving a 20% share of renewable energy in the energy balance. Biogas plant development is also one of the goals set by ?Polityka energetyczna Polski do 2030? (Energy policy of Poland until 2030) and ?Kierunki rozwoju biogazowni rolniczych w Polsce w latach 2010÷2020? [Development directions of agricultural biogas plants in Poland in 2010÷2020]. Biogas production till 2013 is to reach at least 1 billion m3, and till 2020 ? 2 billion m3.
The biogas sector in Poland is still poorly developed though it possesses huge potential. The reasons for that are related to the state of economy and law as well as social aspects. The Energy Regulatory Authority (Urząd Regulacji Energetyki ? URE) data on capacity installed in biogas power plants in 2005?2012 [1, 2] are shown on Figure 1. Recent years have demonstrated a tendency for growth of biogas production in Poland, though it is not sufficient.
According to the data of URE (30.09.2012 r.), 193 biogas power plants are registered in our country, with a total capacity of 124.015 MW. 91 systems work at municipal waste landfills (total capacity: 56.456 MW), while 75 systems with the capacity of 40.503 MW ? in wastewater treatment plants. There are also 26 large agricultural biogas plants in Poland, which produce 26.456 MW of energy (13.5%); their number is continuously increasing. It is estimated that approx. 200 such facilities may be constructed in the upcoming years .
An estimation of the energy potential of biogas
There are no unequivocal guidelines or a strictly determined method of calculating the energy potential of biogas, but all authors in various publications state the significant potential of the biogas sector and forecast its dynamic development. In their studies and forecasts, depending on the needs, the experts apply a theoretical, technical, economic or market potential of using biogas as a renewable energy source. A wide diversification of results in estimating the potential and in the forecasts is related to the method of determining the amount of resources and methodological assumptions. Table 1 shows examples of relevant studies published in recent years.
In order to estimate the biogas potential level, statistical data and indicators available in literature were used. Calculations were made for biogas obtained from various types of biomass, wastewater residues and municipal waste, for all provinces (voivodeships) of Poland [3, 4].
Technical potential of biogas from animal manure
Due to economic reasons and the possibility of obtaining the resource, biogas plants are justified in large farms specialising in breeding animals whose number exceeds 60 livestock units (LU) with a mass of 500 kg/unit.
Basic statistical data for calculations were taken from the GUS study : Użytkowanie gruntów, powierzchnia zasiewów i pogłowie zwierząt gospodarskich w 2009 r. [Land use, crop area and farm animal headage in 2009]. Three basic types of farm animals were taken into account: cattle, pigs and poultry. Large farms, i.e. those owning over 50 head of cattle and/or pigs, were considered. It was assumed that 80% of domestic poultry comes from large farms. In order to convert animal headage into livestock units (LU), the following average coefficients for particular animal species were used : cattle ? 0.8; pigs ? 0.15; poultry ? 0.004. The amount of biogas produced from waste depends on the content of dry organic mass in the waste. The technical potential of producing biogas from animal manure was calculated based on the following formula:
The values of indicators appearing in formula (1) were assumed based on literature data from guide , as average values. For further calculations, the following calorific (energy) value of biogas obtained from animal manure was assumed ? 23 MJ/m3.
Technical potential of biogas from crops and grasslands
Based on statistical data of GUS  and studies of the AEBIOM European Biomass Association, potential of agricultural biogas from crops and grasslands was estimated. It was assumed that maize crops with a weak biogas efficiency per 1 ha, on 5% of arable land surface would be used to produce biogas. Utilisation of biomass from grasslands was estimated to equal 10% of meadow surface and 10% of pasture surface. The following efficiency was assumed: 15 Mg/ha for maize crops and 8 Mg/ha for grass from meadows and pastures. Plant biomass was calculated on dry organic mass and then the amount of methane obtained in those conditions was calculated based on indicators from literature sources .
Technical potential of biogas from sewage sludge
Statistical data from GUS sources  were used to estimate the energy potential of biogas produced from sewage sludge in municipal wastewater treatment plants. Treated wastewater discharged via the sewerage system to the wastewater treatment plant was taken into account. An average unit indicator of the amount of stabilised residues produced in municipal wastewater treatment plants in Poland as given in the National Programme for Municipal Waste Water Treatment  was used ? 0.25 kg of d.m./m3 of treated wastewater. In order to calculate the amount of methane produced in those conditions, the following indicators published in studies by the European Biomass Association  were used: biomethane CH4 obtained from 1 Mg of d.m. of waste ? 260 m3; energy value of biomethane CH4 ? 0.036 GJ/m3.
Technical potential of biogas from municipal waste
In order to estimate the technical potential of biogas from municipal waste, production of biogas from municipal biodegradable waste disposed at large municipal landfills during 1 year was analysed. The amounts of waste disposed at 42 largest landfills were taken into account because biogas production there is economically justified and the data necessary to make the calculations are available.
Based on GUS statistical data , the amounts of municipal waste disposed at landfills in particular provinces were calculated. Morphological composition of the produced waste was taken into account: the indicator of the amount of biodegradable waste was assumed to equal 57% for cities and 36% for rural areas, as given in the National Waste Management Plan . In order to calculate the amount of methane produced in those conditions, the following indicators published in studies by the European Biomass Association  were used: biomethane CH4 obtained from 1 Mg of biodegradable waste ? 130 m3/Mg; energy value of biomethane CH4 ? 0.036 GJ/m3.
Discussion of results
The technical potential of biogas production, estimated per year based on resources from different sources, is shown in Table 2.
Figures 2÷6 show the technical potential of biogas in Poland for particular provinces, produced from different types of biomass coming from animal manure, crops, grasslands, wastewater residues and municipal waste. Poland possesses huge resources for production of agricultural biogas. The energy potential of biogas related to agricultural biomass is estimated to reach approx. 175 PJ/year (48,595 GWh/year). The biggest potential of biogas production from energy crops (maize) exist in the Wielkopolskie, Mazowieckie and Lubelskie provinces, while from permanent grasslands ? in the Mazowieckie and Podlaskie provinces.
The Wielkopolskie province has the biggest potential to produce biogas from animal manure ? approx. 2770 GWh/year (9.97 PJ); the Mazowieckie province is the runner-up in this respect, with a potential of 1460 GWh/year (5.26 PJ). The Wielkopolskie and Mazowieckie provinces may become agricultural biogas production leaders in Poland. In regions with large number of inhabitants using biological wastewater treatment plants, sewage sludge from wastewater treatment plants could be utilised for production and energy use of biogas. These regions include, first and foremost, the Mazowieckie (112 GWh/year (0.4 PJ)) and Śląskie (94 GWh/year (0.34 PJ)) provinces. One should also list the Wielkopolskie, Małopolskie, Dolnośląskie and Łódzkie provinces, where the potential is estimated to equal 67 ? 59 GWh/year (0.24?0.21 PJ).
Regions with large numbers of residents, where large amounts of municipal waste are produced and stored, possess significant resources for production of biomass. These regions include, first and foremost, the Mazowieckie (577 GWh/year (2.08 PJ)) and Śląskie (486 GWh/year (1.75 PJ)) provinces, as well as the Małopolskie (231 GWh/year (0.83 PJ)) and Dolnośląskie (217 GWh/year (0.78 PJ)) provinces.
Poland possesses a large energy potential related to agricultural biomass. The biggest possibilities to produce agricultural biogas from crops exist in the Wielkopolskie, Mazowieckie and Lubelskie provinces, while from grasslands ? in the Mazowieckie and Podlaskie provinces. The Wielkopolskie and Mazowieckie provinces have the Poland?s biggest potential of producing biogas from animal manure. The Wielkopolskie and Mazowieckie provinces may thus become agricultural biogas production leaders in Poland. The Mazowieckie and Śląskie provinces also possess a significant resource potential to produce and utilise biogas from sewage sludge from wastewater treatment plants and from the organic fraction of municipal waste.
The article presents the results of research on the energy biogas potential from different resources in Poland developed within SEBE project – Sustainable and Innovative European Biogas Environment (Central Europe Program) funded by European Regional Development Fund.
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Alina REJMAN-BURZYŃSKA, M.Sc., graduated from the Department of Chemical Technology and Engineering at the Silesian University of Technology in Gliwice; major: chemical process engineering (1974). She is an employee of the Department of Energy Saving and Air Protection at the Central Mining Institute. Specialty: new energy technologies and waste management. email: email@example.com
Halina MAKSYMIAK-LACH ? M.Sc., graduated from the Department of Chemical Technology and Engineering at the Silesian University of Technology in Gliwice. In the years 1975÷2007 she worked for the Department of Water Protection at the Central Mining Institute. She is an external expert in the SEBE project.
Eugeniusz JĘDRYSIK, M.Sc., Eng., graduated from the Department of Chemical Technology and Engineering at the Silesian University of Technology in Gliwice; major: chemical engineering (1974). He is an employee of the Department of Energy Saving and Air Protection at the Central Mining Institute. Specialty: chemical and energy utilisation of coal and biomass.