How is biogas produced?

In biogas plants, decomposition of organic material is a three-step process: In the first phase (hydrolysis) protein, fat and carbohydrates decompose into simpler compounds, like amino acids,sugars and fatty acids. In the second (acetogenic) phase the acetogenic bacteria transform these substances into organic acids with only a few carbon atoms (acetic acid, propionic acid, butyric acid) and hydrogen. Finally, in the third phase (methanogenesis), methane-producing microorganisms break down the acetic acid into methane, carbon dioxide and water, while they also transform part of the produced carbon dioxide into methane.

Thus, there are at least 40-50 different strains of microorganisms to be found in biogas plants, living and working together simultaneously and creating a well organized microbiological food chain, the final product of which are methane and carbon dioxide.

The ratio of organic matter decomposition in biogas plants is about 40-60%, because certain compounds (e.g. cellulose or lignin) decompose less easily. As a result, they would need a much longer residence time in the digester, which would make the overall process not economically feasible.

How can biogas be used?

As the simplest exploitation of the product, biogas was first used for heating, and the primary aim was organic waste management on farms. From the early 90s, biogas plants not only produced heat, but started to generate electricity as well. The efficiency of energy conversion in good, modern combined heat and power stations reach a total efficiency of 85%, from which electric current production is at least 40% and thermal energy about 45%. The produced electric current is fed into the public utility network, while part of the heat energy is needed to heat the digesters. The remaining thermal energy is used locally, e.g., for the heating of buildings, production of hot water, drying of agricultural produce, and various other things.

Biogas can also be fed into the natural gas grid, but only after carbon dioxide and all other contaminating components have been removed. Consequently, and also because of the high costs of compression of the gas and lack of motivating financial support, this type of biogas utilization in Hungary is economically reasonable only in biogas plants of large capacity (1 MW or higher).

Relying on its experience and know-how, the First Hungarian Biogas Ltd. can advise economically viablel solutions with respect to the production of a natural gas quality product (biomethane) to its partners.

In Sweden or Switzerland, the use of biogas as motor fuel is already widespread, which, after appropriate cleaning, is technically possible, but is not yet competitive on the energy market without government subsidy today. Several Swedish cities use biogas for their public transport network, and car owners who have their vehicles transformed so that they run on biogas are subsidized and enjoy other benefits, e.g., free parking, etc.

There are promising prospects of biogas to be used in fuel cells, which are devices that generate electricity at much higher efficacy than CHP, and there are certain types of fuel cells which do not require the removal of carbon dioxide. Intensive applied research and technology development is being carried out in this field in numerous countries around the world.

Is a biogas facility dangerous?

A biogas plant is a closed system, and the biogas produced therein remains within the system, so if plant operation is done with due care and caution, neither the workers nor the environment are endangered. Even if methane escaped into the atmosphere there would be no serious explosion hazard, since methane is lighter than air. According to its characteristics, biogas mixes easily with air. An air-biogas mixture containing 5% methane is explosive, but if a higher air concentration is reached (above 15%), biogas is not flammable anymore. The oxygen concentration in the anaerobic digesters is so low that the content is safe.

Primarily it is not the explosion hazard why biogas needs to be treated with some precaution. If the biogas leaks out the buidings may retain gases, which can build up in confined spaces, and since they are odourless, the gas can be hardly recognized. Consequently, it is highly advisable to ensure good ventilation everywhere (especially in technical rooms) and to use methane leak detectors. Accidents can be prevented by complying with the regulations recommended by the professional technology implementation company. The plant is an explosion-hazardous area, where open flame and smoking are by all means forbidden.

What kind of qualification is needed to run a biogas plant?

There is no specific education needed to run a biogas plant. There are many farmers who operate their own biogas unit on their farm. A biogas plant can be easily fit into the general daily working schedule, which - depending on its size - requires about 1-2 extra working hours per day. In India and China, “family-size biogas plants” have been operating for decades in rural areas using every sort of organic farm waste, and the gas is used for cooking and household heating.

Of course, today’s modern biogas plants cannot be run without acquiring the technological fundamentals, as well as the operational skills of all machines (pumps, mixers and cogeneration apparatus) used in the plant. In Germany, it is often required to present an operator certificate in order to receive bank credit, since this type of qualification guarantees relatively safe plant operation. Special experience and knowledge is required for the analysis of the feedstock, effluent, and indicator compounds of the degradation process. This is usually carried out in designated laboratories at regular intervals rather than buying and operating the expensive equipment on site.

The First Hungarian Biogas Ltd. is always at its partners’ service. We compile the appropriate operational regulations and train the handling crew as well.

Does a biogas plant smell bad?

In case of appropriate operation, a biogas plant does not release any bad odour into the environment. Hydrogen sulfide produced in the course of decomposition is converted to odourless elementary sulfur biologically or chemically in a closed space. Only incoming substrates (like manure, organic waste, etc.) can be a source of bad smell. To eliminate this problem, manure is generally transported and stored in a closed system, while organic waste is unloaded and mixed in a special gas sealed space, which is aired through a biofilter.

In the course of biogas production, microorganisms use the components of manure for their vital processes, which are responsible for bad smell, so fermentation effluent is practically odourless, and it is a good-quality fertilizer for the vegetation.

What happens to the digestion residue?

Decomposition residue or so-called fermentation effluent from biogas production is a practically odourless, homogeneous organic material, free of pathogens and viable weed-seeds, and relative to organic litter or thin manure, has numerous favourable characteristics:

  • Part of the nitrogen fixed in organic compounds turn into inorganic nitrogen in a mineralized form. Consequently, the fermentation residue contains nutrients, which can be easily taken up by plants or soil bacteria,
  • As the dry material content decreases, the density of fermentation residue is lower and the material is more homogenous and is more quickly absorbed into the soil than the untreated animal manure. Therefore bad smell and acid damage, usually associated with traditional manure fertilizing, are significantly decreased.
  • If the fermentor effluent serves as fertilizer, the use of costly nitrogenous, phosphorous or potassium-containing artificial fertilizers in agriculture can be dramatically decreased.

The First Hungarian Biogas Ltd. is ready to share its knowledge about handling and utilization of fermentation residue of the biogas plants with its partners.

How should the location of the biogas plant be chosen?

The most important aspects when choosing the plant’s location are:

  • Short feedstock transportation routes,
  • Utilization of thermal energy generated in CHP stations near the site,
  • az elektromos hálózatra történő csatlakozás lehetősége ill. feltételei,
  • Appropriate security distance from inhabited areas.

When choosing the appropriate location for a biogas plant, it is advisable to consult the First Hungarian Biogas Ltd. beforehand, as it readily helps its partners to assess local conditions on the basis of diverse aspects.

What is the optimal size of biogas plants?

The dimensions of a biogas plant can be characterized by several means. In general practice, it is the electric output in kW that is most frequently indicated. Data from Germany show that the average size of biogas plants in 2000 was 70 kW, while those built in 2002 was already 330 kW. (In Germany and Austria the state support on "green electricity" varies according to the electric output and the used feedstocks.)

The size of a biogas plant can also be characterized by the digester volume. If the total digester volume is under 1500 m3, we talk about small units, while plants with a total volume of 3000 m3 are considered to be big.

The low limit of the size of electricity producing biogas plants is determined by the smallest CHP equipment using biogas (electric output of 10-15 kW). This clearly shows that it is not advisable to build this kind of biogas plant on a farm with less then 50-70 full-grown animals (animals under 500 kg live weight) for manure management if there is not a considerable amount of other organic waste or energy plants specifically cultivated for this purpose. Of course, this consideration does not apply to so-called "family solutions", where biogas is used locally, only for thermal energy generation (heating, cooking).

What can be digested in a biogas facility?

Biogas plants generally process organic matters that decompose easily. These feedstocks can come from agriculture, food industry, or other branches of industry if they fulfil the essencial requirement, that is, if they can be broken down easily by bacteria. The main feedstocks in biogas plants connected to agricultural activity are thin manure slurry or organic litter manure. Thin slurry ensures steady digester operation, as it can maintain almost the same pH value, and thanks to its good buffering capacity it balances the changes in operational parameters due to the addition of other organic materials.

Besides (thin) manure, the following organic materials can be processed in biogas plants with good results:

  • food industry, fruit and vegetable processing waste,
  • distillery waste and residues,
  • by-products of bioethanol and biodiesel production (malt returns, fermented mash, rape-cake, etc.),
  • slaughterhouse and meat packaging waste (e.g. rumen-, stomach-, intestine content, trimmings, expired meat products, etc.),
  • kitchen and restaurant organic waste (e.g. used cooking oil and fat, fat filtration and food remnants, expired products, etc.),
  • wholesale market vegetable waste,
  • plant cultivation waste (e.g. beet leaves, corn-stalk, rotten fruits or vegetables),
  • cut grass, hay,
  • selected solid household organic waste,
  • sewage-sludge,
  • energy plants grown for that purpose (e.g. maize for silage, sweet sorghum, energy grass, different types of beet, Jerusalem artichoke, etc.).

The First Hungarian Biogas Ltd. elaborates for its partnes the most suitable biogas technology on the basis of available feedstocks. Setting up the biogas plant and operating it successfully is possible, even if there is no animal manure among the feedstocks.

Why is biogas production better than composting?

In the course of composting, a process requiring oxygen (aerobic environment), a significant amount of energy is liberated from the decomposing organic material. This is released in the form of heat, while only 5-7 % is used to build new biomass (that is, further microbial cell gowth). In biogas plans, on the contrary, the organic substances are processed under the exclusion of oxygen (anaerobic environment), only about 40% of the chemical energy released from the feedstock molecules is in the form of heat, and 60% is liberated as biogas. Heat is difficult to store, consequently the energy produced in biogas plants is easier to utilize, store and transport, wherefore this alternative has to be favoured whenever the need for treatment of organic waste is necessary.

Then again, biogas plants cannot decompose lignin, so in case of wood, burning or composting are preferable. Slow biomass formation during composting requires high organic matter concentration, and results in slow decomposition, therefore composting remains to be a useful technology in certain cases.

Is modern technology and know-how necessary?

The relatively "simple" technology of biogas plants have lead many to the misconception that a biogas plant can be set up without specific technological knowledge and experience. This oversimplification of the technology has resulted in numerous operational failures. As a result of inappropriate operation, two thirds of all German biogas plants are less economical than they should be and keep running with the help of significant state subsidy. Just like in case of keeping livestock, economical and reliable operation can only be ensured if the operator has proper knowledge as far as feedstock quality and key operation conditions are concerned. Besides the required knowledge, the operator has to be a conscientious manager as well, since neglecting his duties might lead even the most up-to-date biogas plant into the red.

It is advisable and remunerative to have an expert decide the biogas plant’s size, design and choose the most appropriate digesters, mixing apparatus, the best feedstock-pretreatment method and organize material streams, etc. A predetermined feedstock combination and keeping the recommended proportions further secure plant operation, help to prevent possible breakdowns in biogas production and ensure steady biogas quality and quantity. Processing animal waste requires special expertise, since breaching the strict health authorities’ regulations might result in shutting down the plant.

On the basis of good relations to its Western European business partners and its own professional experience, the First Hungarian Biogas Ltd. can elaborate and realize the most up-to-date and most effective biogas concepts.

Why are there so few biogas plants in Hungary?

In certain Western European countries, general uses of biogas technology, government commitment, legislation, as well as economics are closely connected. Biogas industry is especially highly developed in those countries (e.g. Germany, Austria, UK, Denmark Sweden and the Netherlands), where economic policy efficiently subsidizes the increased use of renewable energy resources and environmental protection. In Germany, after amending the regulation of electricity production from renewable energy resources (Erneuerbare Energien Gesetz, 2004), biogas plants started to proliferate. As the legal framework shifted into a positive direction, switch to renewable energy production became a profitable option for farmers as well. Similar conditions regarding the support for “green electricity” were created In Austria, promoting the general use of biogas technology. In other European countries, like in France for example, there are hardly any biogas plants. (According to the EU Biogas Barometer, the EU’s top biogas producer is the UK, where the strict regulations request compulsory collection of landfill gas.)

In Hungary, there is government subsidization, but in its present form and extent it is not enough for substantial improvement and escalation of this technology. Recognition of the advantages of biogas technology in the field of energy supply, environmental protection and soil management will hopefully contribute to the creation of a favourable economic environment.

How much land is needed to dispose of the residue?

The easiest and most effective way of utilizing digester effluent is increasing the production capacity of plough-lands as fertilizer. The size of necessary arable land is primarily determined by the nitrate nitrogen content of decomposed remnants. The amount of nitrogen per one hectare cannot exceed 170 kg.

In case of biogas facilities processing energy plants (such as maize for silage, sweet sorghum, Jerusalem artichoke, rye grass, etc.) the capacity of arable land needed for feedstock cultivation is generally large enough for the intake of fermentation residue.

In the course of investment preparation, the First Hungarian Biogas Ltd. studies the conditions of setting up the biogas plant in the given environment, and recommends the most economical solutions.