Producing biogas at home. The role of anaerobic bacteria in the production of biogas from waste

In total, about 60 types of biogas production technologies are currently used or developed in the world. The most common method is anaerobic digestion in digesters, without access to air, or in anaerobic columns. Part of the energy obtained from biogas utilization is used to maintain the process. In countries with hot climates there is no need to heat the digester. Bacteria convert biomass into methane at temperatures from 25 to 200°C. The process is based on decomposition (rotting) under the influence of bacteria belonging to two large families: acidogens and methanogens, pre-sorted solid waste (organic waste, thick dirt) in metal containers without air access at average temperature about +55°C. The resulting gas is supplied under pressure to the purification system, and then released into two components SCC (methane) and CO 2 (carbon dioxide). Biogas consists of 55-75% methane CH4, 25-45% CO 2, including small impurities H 2, H 2 S and organic matter. The period of formation of high-quality biogas is 7-15 days.

Biogas production helps prevent methane emissions into the atmosphere. Methane has an impact (greenhouse effect) 21 times stronger than CO 2 and remains in the atmosphere for 12 years. Capturing and using methane is the best short-term way to prevent global warming.

Russia annually accumulates up to 300 million tons of dry equivalent organic waste: 250 million tons in agricultural production, 50 million tons in the form of household waste. These wastes are the raw material for biogas production. The potential volume of biogas produced annually could be 90 billion m3.

Biogas is collected, preventing air pollution, and used as fuel to produce electricity, heat or steam, or as automobile fuel. In India, Vietnam, Nepal and other countries, small (single-family) biogas plants are being built. The gas produced in them is used for cooking. At the end of 1990, China produced about 7 billion m3 of biogas per year. In 2006, this volume increased to 15 billion m3.

Among industrialized countries, Denmark takes the leading place in the production and use of biogas - biogas occupies up to 18% of its total energy balance. IN Western Europe at least half of all poultry farms are heated with biogas.

Volvo and Scania produce buses with biogas engines. Such buses are actively used in the cities of Switzerland: Bern, Basel, Geneva, Lucerne and Lausanne. According to forecasts of the Swiss Gas Industry Association, by 2010, 10% of Swiss vehicles will run on biogas.

Taking into account our conditions, methane produced from biogas, or biogas in its main form, can be used as fuel for small boiler houses, vehicles and electricity generation. Next to the solid waste processing plant, it is planned to build modules - greenhouses for growing crops Agriculture, vegetables and herbs.

The released methane from biogas is the raw material for many valuable products chemical industry- methanol, formaldehyde, acetylene, carbon disulfide, chloroform, hydrocyanic acid, soot

From 1 ton of solid and liquid household waste using anaerobic digestion technology (HSAD) produces 521 m 3 of biogas. Pure methane has a calorific value of about 35.9 MJ/m 3 at 0°C and 101.3 kPa. 1 million British thermal unit Btu (MJ) corresponds to 293 kWh.

Let's consider an example of calculations for gas output in accordance with the American technology of anaerobic digestion HSAD. Available 100 tons municipal waste:

• 45% waste for digestion (fecal sludge, household waste, cardboard)
• 55% waste for sorting (glass, metal, plastic, wood, minerals)
• 45 tons of waste = 18800 m 3 of biogas (80% renewable standard)
• 11300 m 3 methane (60%) or 398 million Btu;
• 5400 m 3 С0 2 (30%).

At 35% efficiency, 60% methane produces 139 million Btu or 40,727 kW per day.

From 137 tons of waste the following is produced:

• 2525600 tons of compost per year
• 22.9 million liters of methane or 17 tons per day (65% of the total mass of gas produced, 30% - CO 2)
• 810 million Btu per day.

The yield of biogas per 1 ton of absolutely dry matter depends on the type of raw material used. It is economically most justified to obtain biogas from waste from livestock farms. From a ton of large manure cattle 200-350 m 3 of biogas with a methane content of 60% is obtained, 300-630 m 3 of biogas from various types of plants with a methane content of up to 70%.

Biogas calculations even use the concept of “animal unit” to be able to compare the amount of biogas produced from the manure of different animals. One animal unit produces about 0.5 m 3 of biogas per day. One animal unit corresponds to 1 adult cow / 5 calves / 6 pigs / 250 chickens.

Raw materials for processing into biogas: waste meat industry, liquid municipal waste, agricultural waste, wood waste, cardboard, food waste, organic waste - grass, straw, leaves, pine needles, manure, fecal sludge, household waste, cardboard. Final product processing: biogas, high-quality compost.

Currently, the total amount of methane in the atmosphere is estimated at 4600-5000 Tg (Tg = 1012 g, or 1 Tg of methane corresponds to 1012 grams of carbon dioxide). Since methane certainly has a stronger greenhouse effect than carbon dioxide, their emissions were compared by recalculating the effect of methane and the effect of CO? using the so-called CO equivalent? (one ton of methane emitted is equivalent to 23 tons of CO emitted? on a time scale of 100 years). IN southern hemisphere methane concentrations are slightly lower than in the northern hemisphere. This difference is usually attributed to the smaller power of methane sources in the southern hemisphere: the main sources of methane are believed to be located on the continents, and the oceans do not make a significant contribution to the global methane flux. The lifespan of methane in the atmosphere is 8-12 years.

Methane enters the atmosphere from both natural and anthropogenic sources. The power of anthropogenic sources currently significantly exceeds the power of natural ones. TO natural sources methane includes swamps, tundra, reservoirs, insects (mainly termites), methane hydrates, geochemical processes (volcanic eruptions); anthropogenic - rice fields, mines, animals, losses during gas and oil production, biomass burning, landfills.

The intensity of methane release from swamps varies widely. Methane emissions from western Siberian swamps which are enough typical representative northern swamps, determined using gas chromatography methods, is approximately 9 mg of methane per hour/m2. On average, methane emissions from Siberian swamps can reach 20 Tg/year, which is quite a lot compared to the total methane flux from swamps (50-70 Tg).

The number of cattle in the world is about 1.5 billion heads. One cow produces about 250 liters of pure methane per day. This amount of methane is enough to boil 20 liters of water. IN developed countries Approximately 1.8 kg of garbage per day per person is disposed of in landfills; in Russia, 0.6 kg, respectively. Approximately 10% of this mass can be converted into methane. Consequently, Russia produces 60 g of methane per day per person.

Above was an example of American anaerobic digestion technology, which gives good results by biogas output. Domestic experience shows that on average, the decomposition of one ton of solid waste can produce 100-200 m 3 of biogas. Depending on the methane content, the lower calorific value of landfill biogas is 18-24 MJ/m 3 (about half calorific value natural gas).

Annual methane emissions from landfills globe comparable to the power of such well-known sources of methane as swamps, coal mines, etc. Today, there is an acute problem of stabilizing the concentration in the atmosphere of this gas, one of the main planetary sources of the greenhouse effect. Therefore, the utilization of biogas from household waste acquires vital importance to reduce anthropogenic methane emissions. In addition, methane causes spontaneous combustion of landfill deposits, since its interaction with air creates flammable and explosive mixtures, which leads to severe pollution of the atmosphere with toxic substances.

Since the process of waste decomposition continues for many decades, the landfill can be considered as a stable source of biogas. Biogas emissions from a landfill, depending on the volume of landfill mass, can range from several tens of l/s (small landfills) to several m3/s (large landfills). The scale and stability of formation, location in urbanized areas and low cost of production make biogas produced at solid waste landfills one of the promising sources of energy for local needs. As shown above, the utilization of biogas at solid waste landfills requires engineering arrangement of the landfill (creation of an insulating screen, gas wells, gas collection system, etc.). At the same time, the main task of environmental protection in urbanized areas is solved - ensuring cleanliness atmospheric air and preventing groundwater pollution.

Biogas generated at landfills since the early 1980s. It is intensively mined in many countries. Currently, the total amount of biogas used is approximately 1.2 billion m 3 /year, which is equivalent to 429 thousand tons of methane, or 1% of its global emissions.

In Germany, 409 large municipal waste landfills have collection points for biogas generated by the decomposition of organic components of waste. On average, about 100 m 3 of biogas is produced from 1 ton of waste at landfills in Germany. With a total volume of biogas released from landfills in the amount of 4 billion m 3 /year (which is equivalent to 2 billion m 3 of natural gas), its useful consumption is about 400 million m 3 /year. Biogas, after its purification, is used to obtain electrical and thermal energy used for industrial purposes and in heating systems. The amount of biogas generated in landfills ranges from 10 to 1200 m 3 /h. The power of installations for producing electricity from biogas ranges from tens of kW to several thousand kW, which makes it possible to provide energy from several houses to a small village. Biogas is often used as fuel in power plants with internal combustion engines (ICE). The cost of energy obtained from combustion engines is approximately 2-2.5 times lower than electricity tariffs for the population.

In the USA, the current volume of biogas production is 500 million m 3 /year. A significant part of biogas goes to power plants operating on gaseous fuel. The total electrical power of biogas-fired installations is about 200 MW. In addition, biogas is increasingly supplied to public gas networks.

In the UK, about 200 million m 3 /year of biogas is produced. The total capacity of UK bio-energy systems is about 80 MW.

In France, about 40 million m 3 /year of biogas is produced. At one of the landfills near Paris, a Biothermal Power Plant was built, using biogas, the emission of which is 1500 m 3 /day.

In Ukraine, about 10 million tons of household waste are generated annually in cities. More than 90% of solid waste is transported to 655 landfills and landfills, of which 140 are suitable for the extraction and use of landfill gas. The potential of landfill gas is about 400 million m 3 /year.

Utilization of biogas is very promising for Russia, since about 97% of the 30 million tons of waste generated annually is buried in landfills and organized landfills. There are more than 1,300 solid waste landfills in operation in Russia. The annual emission of methane from landfills in Russia is estimated at 1.1 billion m3 (788 thousand tons), which is almost twice the current consumption in the world.

Currently, landfill biogas is practically not used in Russia. As part of the Russian-Dutch project in the period 1995-1997. At the Dashkovka and Kargashino landfills, located in the Moscow region, two pilot installations for the production and utilization of biogas were built. The results obtained show that at an average landfill in the Moscow region, up to 600-800 m 3 /h of biogas is formed, which makes it possible to generate electricity in the amount of 3500-4400 MWh/year. Technical and economic calculations performed on the basis of experimental data have confirmed the effectiveness of landfill methane production in Russia, where hundreds of economically profitable projects can be implemented.

In St. Petersburg, about 5 million cubic meters of solid waste are generated annually, of which about 80% is disposed of at three existing landfills. The most preferred landfill for biogas utilization is the Volkhonsky PTO-1 landfill, one of the largest in Russia. This landfill mainly disposes of household waste; its capacity is almost exhausted; reclamation work is planned, which can be combined with the creation of a biogas system. Calculations have shown that the expected methane emissions will be sufficient to operate a thermal power plant with a capacity of 2000 kW for 20-25 years. In addition, on the territory Leningrad region There are 55 organized landfills, where about 1 million m3 of solid waste are disposed annually. Despite the relatively small volumes of waste disposal, the production of biogas at a number of landfills can be profitable due to the high cost of fuel.

Rice. 72.

Anaerobic breakdown of organic matter into garbage dumps occurs under the influence of methanogenic bacteria and leads to the release of methane, amounting to 5-20% of the total global emission of this gas into the atmosphere.

As already indicated, the formation of gases at landfills (landfills) of household waste is associated with the occurrence of anaerobic microbiological reactions with the organic components of household waste. These gases contain predominantly methane, carbon dioxide and nitrogen. In addition, foul-smelling gases are formed - hydrogen sulfide (H 2 S), mercaptans (R-SH), aldehydes (R-CHO) in varying concentrations. The gas composition depends on the duration of storage and the fermentation phase. The aerobic phase occurs over a period of several weeks, while anaerobic acid fermentation (rotting) can continue for several years. In Fig. 72 shows the individual phases of fermentation. The specific release of gases at landfills in Germany is estimated at 60-180 m 3 /t of waste.

Rice. 73. One of the schemes for the oxidation of organic waste

10.1. General information about biogas production

In the last decade, much attention has been paid to the development in our country of the use of non-traditional and renewable energy sources due to the shortage of its own fuel and energy resources. One of the non-traditional and renewable energy sources can be energy obtained from biomass. It is the biogas obtained on the farms of the republic and the production of energy from it that will allow saving natural and liquefied gases.

All sources of biomass can be divided into three main groups:

to the first group These include land plants specially grown for energy purposes. Silvicultural energy farms are of the greatest importance for growing various tree species: a fast-growing willow species (developed by Belarusian scientists), ebony, eucalyptus, palm tree, hybrid poplar, etc. One of the promising energy crops is the Jerusalem artichoke, sweet sorghum, and sugar cane.

To the second group biomass sources include various organic residues and wastes:

a) animal biological waste (cattle manure, poultry droppings, etc.);

b) residues from harvesting agricultural crops and by-products of their processing, such as rye and wheat straw, corn cob, cotton stalk, peanut shell, potato waste, rice husks and straw, seed husks, flax husks, etc.;

c) waste from logging, sawmilling and wood processing: bark, sawdust, wood chips, shavings;

d) industrial wastewater (in particular, textile, dairy, and other food processing enterprises);

e) municipal waste (solid and waste water).

Third group– these are aquatic plants, including seaweeds, including giant kelp (brown algae) and water hyacinth. The ocean is seen as the main supplier of large marine brown algae and algae living on the bottom (benthic plants), as well as algae floating in stagnant water. In addition, the possibility of using biomass from the estuary of salt and freshwater marshes is analyzed.

The energy potential of aquatic plants is quite high. For example, fresh seaweed 29.2 t.e./ha/year; water hyacinth -53.6 t.o.e/ha/year, and sugar cane 40.0 t.o.e/ha/year /21/, /26/.

Depending on the humidity and degree of biodegradability, biomass is processed by thermochemical methods (direct combustion, gasification, pyrolysis, liquefaction) or biological methods (anaerobic processing, ethanol fermentation). With their help, various final energy products can be obtained from biomass, including heat, steam, low- and high-calorie gases and various liquid fuels. One of the most widely used methods for processing biomass remains direct combustion to produce heat or electricity. The most promising processes for converting biomass are thermochemical gasification, fermentation and anaerobic processing, which results in synthesis gas (methane). The development of bioenergy based on a renewable energy resource such as wood may be promising for Belarus. This includes the cultivation of fast-growing varieties of wood. In Belarus, research is already underway on growing energy plantations of Canadian willow and Sakhalin knotweed Weirich. These trees are capable of renewing themselves within 25 years, and cutting and fuel collection are carried out after 3 years, and one hectare of plantation can produce an average of 20 m3 of wood. The possibilities of growing and the feasibility of growing Sakhalin bamboo and Sylvia latifolia in our climatic conditions are also being studied. The technology of burning wood pellets is being developed and widely used.

10.2. Producing biogas from anaerobic digestion

One of the ways to produce biogas is the method anaerobic(without oxygen), fermentation or fermentation(overheating) of organic substances of biological mass of various origins at a temperature of 30÷370 ° C, as well as with constant stirring of the loaded raw materials, periodic loading of the raw materials into a container for fermentation and unloading of the fermented material /17, pp. 357-364/. The container in which the fermentation process occurs is called digester or reactor. If all the above conditions are met, under the influence of bacteria present in the biomass, organic substances decompose and form a mixture of gases, which is called biogas.To produce biogas, waste from processing agricultural crops can be used - silage, straw, food and other farm waste, manure, bird droppings, Wastewater and similar raw materials containing organic substances. It is important that the environment of the raw materials is neutral, without substances that interfere with the action of bacteria, such as soap, washing powders, antibiotics / 20/.

Biogas contains 50÷80% methane (CH 4), 50÷20% carbon dioxide (CO 2), 0÷3% hydrogen sulfide (H 2 S), as well as impurities: hydrogen, ammonia and nitrogen oxides. Biogas does not have an unpleasant odor. The heat of combustion of 1 m 3 of biogas reaches 21÷29 MJ, which is approximately equivalent to burning 0.6 liters of gasoline, 0.85 liters of alcohol, 1.7 kg of firewood or using 1.4÷1.6 kWh of electricity. The efficiency of fermentation depends on compliance with anaerobic conditions, temperature conditions and the duration of fermentation. Fermentation of manure is possible at a temperature of 30÷35 °C ( mesophAndline directorAndmfermentedAndI) and 50÷60°С and above ( thermofAndline directorAndm).

The duration of manure fermentation depends on the type of biomass. For cattle manure and chicken manure, the duration is 20 days, for pig manure - 10 days. The activity of the microbial reaction is largely determined by the ratio of carbon and nitrogen. The most favorable conditions with the ratio C/N== 10:16.

From 1 m 3 of reactor, the biogas yield reaches 2÷3 m 3 of biogas, from bird droppings - 6 m 3 /21/. The following amount of biogas can be obtained per day from one animal: cattle (weighing 500÷600 kg) -< 1,5 м 3 ; свиньи (массой 80÷100 кг) - 0,2 м 3 ; куры или кролики - 0,015 м 3 .

Data on the specific yield of biogas from various agricultural wastes are given in Table 15.1 /17, p.357/.

The energy obtained from burning biogas can be used for various agricultural needs. Using an electric generator driven by a gas internal combustion engine, electricity can be generated. The disadvantage is that part of the generated energy must be used to operate the biogas plant itself (in some installations up to 50% of the generated energy).

Biogas can be burned as fuel in burners of heating installations, hot water boilers, gas stoves and used in absorption-type refrigeration units, in automotive engines, and in infrared radiation units. A carburetor engine can easily be converted to gas, including biogas. To do this, the carburetor is replaced with a mixer. Converting diesel engines to gas operation is not difficult. When switching from diesel fuel to natural gas, engine power is reduced by 20%, from natural to biogas - by 10%. Biogas consumption is on average 0.65 m 3 /kW h. The gas pressure in front of the engine must be at least 0.4 kPa /17, p. 358/.

In livestock farming for heating water, the need for biogas per animal per year is: dairy cow - 21-30 m 3, pig - 1.4-4.9 m 3. Larger values ​​of these figures refer to small farms, smaller ones - to medium-sized ones.

Table 15.1.

Biogas yield from organic waste

The need for biogas for heating milking parlors is equal to: with the number of cows 40 - 164/327 m 3 /year; with a number of cows of 60 - 212/410 m 3 /year; with a number of cows of 80 - 262/530 m 3 /year. The numerator contains data at an outside air temperature of up to - 10 ° C, and the denominator - at an outside air temperature t below - 10 ° C.

To heat poultry houses at an external temperature of - 10 ° C and an internal temperature of 18 ° C, approximately 1.2 m 3 / h per 1000 birds is required.

The residue (methane mash) can be used as fertilizer.

B And gas installations And (BSU), depending on the characteristics of the technological scheme, are of three types: continuous, periodic and accumulative /17, p.360/.

With a continuous (flow) scheme (Fig. 15.1), fresh substrate is loaded into the fermentation chamber continuously or at certain intervals (from 2 to 10 times a day), removing the same amount of fermented mass. This system allows you to obtain the maximum amount of biogas, but requires more material costs.

With a periodic (cyclic) scheme (Fig. 15.2), there are two fermentation chambers, which are loaded in turn. In this case, the useful volume of the chambers is used less efficiently than with continuous. In addition, significant supplies of manure or other substrate are needed to fill them.

With an accumulative scheme, the manure storage facility simultaneously serves as a chamber for fermentation and storage of fermented manure until it is unloaded (Fig. 15.3).

Methane “fermentation”, or biomethanogenesis, the process of converting biomass into energy, was discovered by Europeans only in 1776 by Volta, who established the presence of methane in swamp gas. The biogas produced by this process is a mixture of 65% methane, 30% carbon dioxide, 1% hydrogen sulfide and trace amounts of nitrogen, oxygen, hydrogen and carbon monoxide. (A. Sasson)
First information about practical use Biogas produced by Europeans from agricultural waste dates back to 1814, when Davy collected biogas while researching the agrochemical properties of cattle manure. To collect waste, starting in 1881, closed containers began to be used, which, after slight modification, were called “septic tanks”. Back in 1895, street lamps in one of the areas of the city of Exeter (England) were supplied with gas, which was obtained as a result of fermentation of wastewater. Since 1897, water purification in this city was carried out in such containers, from which biogas was collected and used for heating and lighting.
Currently, bioreactors of various designs are known, which provide for the strength of the material from which the installation is created, devices for mass mixing and heat transfer, preparation and heating of the loaded substrate, intake and accumulation of biogas and sediment removal.
Since December 1, 2000, the Karaganda EcoMuseum has been implementing the “BIOGAS” project to introduce biogas technologies in the Karaganda region. This project is the first experience in using biogas technologies in Central Kazakhstan. During the implementation of the project, the Ecological Museum has accumulated quite a lot of experience and information about the construction, startup and operation of biogas plants, and this experience is tied to the local conditions of Central Kazakhstan, where similar technologies have not previously been used.
Employees of the Karaganda Ecological Museum have developed and implemented several technologies for the construction of biogas plants, adapted for peasants and farmers of Kazakhstan.

Why do we need biogas?
Biogas is a metabolic product of methane bacteria, which is formed as a result of the decomposition of organic matter.
Biogas is a high-quality and complete carrier of energy and can be used in many ways as fuel in households and in medium and small businesses for cooking, generating electricity, heating residential and production premises, boiling, drying and cooling. The average combustion heat is 6.0 kW/h/cub.m
The extent to which biogas can replace traditional fuel depends on the volume and efficiency of the plant. The Karaganda experience of using BGU shows that an installation with a volume of 8 cubic meters. m. and running on pig manure can completely replace propane gas used for cooking in a family of five. A BGU with a volume of 60 cubic meters can be used to heat residential premises with an area of ​​200 sq.m and an industrial premises with an area of ​​400 sq.m.
When operating a biogas plant, waste raw materials are also useful product, capable of improving the economic and environmental conditions of peasant or farm. Biosludge is a high-quality fertilizer, raw material for the production of vermicompost, a substrate for growing mushrooms. And with appropriate installation parameters and control over compliance with the temperature regime of operation, the BGU is a feed additive for animals that require animal protein for normal development (pigs, chickens, etc.) and complementary food for fish in fish farms.
To summarize, the use of biogas technologies can bring the following benefits:

Saving time and labor
- Reduces cooking time
- Reduces time spent washing dishes
- Reduces time spent cleaning the kitchen
- Time spent on stove maintenance is freed up (cleaning the stove from ash, removing ash, bringing in fuel, loading the stove, ignition, monitoring the stove and adding fuel)
- Time previously spent on collecting, transporting, drying and storing dung or searching, transporting and reloading coal, and searching, purchasing, cutting, drying and storing firewood is freed up
- The time for weeding is reduced (their seeds die in the storage tank)

Saving money
- Saves money spent on heating oil or electricity
- Extends the life of kitchen utensils
- Save money on the purchase of fertilizers and herbicides

Possibility of receiving additional money
- You can sell excess gas to your neighbors or exchange it for something
- You can sell compost
- When using compost, the productivity of your agricultural crops increases and you can help more money from their sale.

Environmental benefits
- Reducing emissions of methane (greenhouse gas) into the atmosphere
- Reducing the amount of coal, wood or fuel burned to generate electricity, and as a result, reducing the generated carbon dioxide (greenhouse gas) and harmful combustion products
- Reduced reset in environment polluted waters
- Purification of polluted waters from organic substances and microorganisms
- Preservation of forests from deforestation
- Reduced need for chemical fertilizers
- Cleaning the air in the house and village from coal combustion products
- Reducing air pollution by nitrogen compounds, air deodorization

Space saving
- Frees up space previously occupied by coal or dung

Facilities
- Purifies the air in the house and kitchen
- The volume of unused garbage is reduced (there is less garbage)
- All organic waste is used, including toilet waste
- There are fewer weeds in the garden and field, their seeds die in the storage tank
- The smell from manure in the yard is reduced (the bioaccumulator is anaerobic, that is, it does not have contact with air)
- Reduces the number of flies

Staying healthy
- Reduces the risk of contracting diseases associated with polluted air - respiratory and eye diseases
- The epidemiological situation is improving due to the death of microorganisms in the reservoir and the reduction of insect breeding sites
In order to understand what benefits and profits the operation of a biogas plant can bring in your specific farm or peasant farm, you must understand:
1. how much costs will be required for the construction of a biogas plant,
2. how can these costs be reduced?
3. and how long will it take for these costs to pay off.
Answers to the questions posed can be obtained by compiling detailed plan construction of the installation, its operation and sale of the resulting products.

WHAT ARE BIOGAS INSTALLATIONS?
For clarity, here are a few definitions of commonly used terms in this chapter:

Bioreactor- a reservoir (vessel, container) in which conditions are created for the life of methane-generating bacteria. As a synonym for the term “reactor”, some literature uses the terms “reactor”, “methane tank”, “methane tank”, “septic tank” - they all have the same meaning

Heating system - a steam (water) heating system that allows you to maintain the operating temperature in the bioreactor, especially in winter period.

Mixing device - a device located inside the bioreactor and allowing mixing of the processed mass to speed up complete processing.
Loading and unloading openings are openings in the bioreactor through which raw materials are loaded and processed biomass is unloaded.
All biogas plants are divided into two types according to their operating cycle: continuously operating and periodically operating.
Continuously operating biogas plants are constantly loaded with raw materials, and at the same time processed biomass is shipped. Thus, the operation of the installation is not interrupted.
Biogas plants operating periodically or cyclically are loaded completely to the operating level and hermetically sealed, for a certain period of time the plant actively releases biogas, after complete processing of the biomass the plant is unloaded and the operating cycle is repeated.
The shape of the reactor and the building materials used. During the implementation of the project, biogas plants were developed that could operate in the conditions of Central Kazakhstan.
Cylindrical biogas plants are located horizontally if the plant is of a continuously operating type, and vertically if the plant is cyclically operating.
Ellipsoidal biogas plants have a shape close to egg-shaped. From the point of view of the biomethanogenesis process, this form of bioreactor is the most optimal - natural mixing processes occur in it, as well as sludge removal and sediment runoff. Biogas plants of a similar shape are built from concrete or built from brick.
Equipment used for biogas production. To increase the biogas yield from the installation, additional equipment is used:
1. Sewage pumps are used for pumping out processed biomass and greatly facilitate the maintenance of a biogas plant.
2. Circulation pumps are used in the heating system of the installation and allow maintaining operating temperature with lower energy consumption.
3. Mixing devices are used to mix the processed biomass inside the reactor, which increases the productivity of the installation and reduces the time required for processing biomass.
4. A check valve installed in the gas exhaust system is necessary to prevent air from entering the bioreactor.
5. Gas heating boiler, connected to the heating system of the installations and runs on emitted biogas and consumes up to 5% of the total amount of gas.

BSU productivity
As noted earlier, the products produced by biogas plants are biogas and biosludge.
Biogas productivity - biogas output (m3) per unit of substrate (m3) during the fermentation period.
Biogas productivity depends on the following parameters:
- volume of the reactor of the installation; the larger the installation volume, the greater the gas output
- temperature in the reactor at which fermentation occurs; Methane-forming bacteria in oxygen-free conditions can release gas in the temperature range from 0C to 70C. However, biogas is released most intensively in 2 temperature ranges. It should be noted that when different temperatures"work" different kinds methane-generating bacteria. The first interval (mesophilic, because mesophilic bacteria work) from 25C - 38C - optimal temperature 37C. The second interval (thermophilic, because thermophilic bacteria work) from 45C - 60C - the optimal temperature is 56C. Each of these intervals has a number of advantages and disadvantages, which can be found in detail below.

MESOPHILIC TYPE OF FERMENTATION

pros
- Gas productivity practically does not decrease when the temperature deviates by 1-2oC from the optimum;
-Less energy costs are required to maintain temperature.

Minuses
- Gas release is less intense;
- It takes more time until the substrate completely decomposes - 25 days;
- Biosludge obtained in this mode is not completely sterile.

THERMOPHILIC TYPE OF FERMENTATION

pros
- Gas release is more intense;
- It takes less time until the substrate completely decomposes - 12 days;
- The biosludge obtained under this mode is completely sterile and therefore can be used as feed additives for animals.

Minuses
- Gas productivity decreases significantly when the temperature deviates by 1-2oC from the optimum;
- More energy is required to maintain temperature.
- from raw materials. The raw materials for BGU can be domestic animal manure, plant matter and other organic residues. Depending on the substrate used, the productivity of biogas varies. Approximate data are shown in table No. 1

Table No. 1. Biogas productivity depending on the raw materials used during the fermentation period (Archea 2000, Germany).

Operation of biogas plants
1.The installation is started in several stages.
Initially, the installation is loaded with raw materials, very important aspect This action is determined by the humidity of the loaded substrate - it should be 85% in winter, and up to 92% in summer. The installation is loaded up to the water seal. To speed up the start of the methanogenesis process, a starter (biosludge or substrate from a working installation) is poured into the loaded substrate. In the absence of a starter, fresh cattle manure is added to the substrate.

The frequency of loading the substrate is determined experimentally for each biogas plant; this parameter depends on many indicators: the temperature of the substrate, the type of animal producing the raw materials, the humidity of the substrate, the volume of the installation, etc. The raw materials are brought to the optimal humidity before loading into the plant. The substrate is diluted warm water(35-40 degrees) is thoroughly stirred and then poured into the loading hole of the installation. The moisture content of the raw material determines the volume of biogas output, the processing time of the raw material and the degree of its decomposition. IN summer period Optimal humidity is 92%; in winter, 85% humidity is optimal.
3. Maintaining optimal temperature.
In the conditions of Central Kazakhstan, it is necessary to heat up the operating reactor. During construction, tubular heat exchangers are installed inside the reactor, which, depending on the design of the installation, are supplied either to the steam heating of a residential building (small-volume installations) or to an autonomous heating boiler running on biogas. To reduce heat loss, the loaded substrate is diluted with hot (temperature no higher than 60°C) water.
4. Mixing.
Mixing the substrate inside the reactor significantly increases the efficiency of the BGU, as it prevents the formation of sediment and floating crust and ensures the movement of mass in the reactor.
5. Biogas accumulation.
Since biogas is consumed unevenly, and the installation produces it constantly, the question of its accumulation arises. The gas can be collected in rubber bladders used in the wheels of agricultural machines.
6. Use of biogas.
Biogas is used for cooking, heating residential premises, heating industrial premises (greenhouses, poultry houses, etc.).
7. Use of biosludge.
Biosludge is used as fertilizer in the fields of the farm; when the substrate is completely processed in the reactor of the installation, biosludge can be used as an additive in feed for pigs and poultry. After simple processing (filtration and drying) of biosludge, it can be sold for commercial purposes. Potential buyers of biosludge fertilizer are gardening farms, dacha cooperatives, etc.
8. Safety precautions.
Biogas contains hydrogen sulfide (H2S), carbon dioxide (CO2) and methane. Methane, which is part of biogas, is practically non-toxic. It is lighter than air, flammable and forms an explosive mixture with air (5-15% methane) or oxygen. In the event of a leak, in the presence of ventilation, the gas evaporates without any consequences. Hydrogen sulfide, even if it poses a danger to human health, is found in small quantities and is easily detected by its unpleasant odor. Since hydrogen sulfide is heavier than air, care must be taken to ensure that during leaks this gas cannot accumulate in recesses. At high concentrations, it dulls the perception of odor, which makes it difficult to detect and can lead to fatal poisoning, but once again it can be noted that the proportion of hydrogen sulfide in biogas is very small and amounts to no more than 1%. Carbon dioxide (CO2), which is part of biogas, can also accumulate in deep recesses, since it is heavier than air, causing a suffocation hazard if there are leaks in the installation.

Conclusion
If you were interested in this information in our brochure, and you decided to build a biogas plant on your farm, then I would like to give you some more tips and recommendations.
Tip #1. Before constructing a plant, think carefully about the use of biosludge. The shape of the reactor depends on this and temperature regime. In the case of using biosludge as fertilizer, the cost of maintenance and construction is reduced. In the case of using biosludge as food additives for livestock and poultry, the cost increases, but the payback time decreases. Livestock and poultry receiving such supplements gain weight faster, mortality decreases, due to which you can make a profit in the home (peasant or farm) economy.
Tip #2. Having decided on the shape and volume of the reactor, you can begin to draw up your construction estimate. Having drawn the line “total”, do not immediately grab your head from the high amounts. The cost of installation can be significantly reduced by using, in some cases, junk or “time-tested” construction material.
Tip #3. Having prepared a list of necessary building materials, you may not find something in your city or area. Consult us, we can tell you what building material can be used to replace the one not found.

Anaerobic bacteria- these are microorganisms that use oxygen in minimal quantities for their vital functions.

Typically, living beings use inhaled oxygen to oxidize organic matter (carbon is oxidized, oxygen is reduced). However, in areas poor in oxygen, there are anaerobic bacteria that do without oxygen and use some other oxidizing agent.

Anaerobic microorganisms were discovered by the French scientist Louis Pasteur in 1861. This discovery became a sensation for biologists who believed that life is impossible without respiration and the use of oxygen.

Later it turned out that spore-forming anaerobes are not some rare wonders, but very widespread organisms throughout the entire surface of the Earth. Subsequent studies by many microbiologists showed that a wide variety of natural environments, including those completely devoid of molecular oxygen, are inhabited by many microscopic organisms that take an active part in the cycle of substances on Earth.

An in-depth study of the metabolism of anaerobes has made it possible to use them in industry as producers of a number of valuable substances. National economy connections.

Currently, industry and residential areas produce a large number of waste that needs to be disposed of and recycled. Biogas can be obtained from organic waste. Under anaerobic conditions, bacteria decompose organic substrate, and biogas is an intermediate product of their metabolism.

About 60 types of biogas production technologies are currently used or developed in the world. The most common method is anaerobic digestion in metatanks (biological processing tanks), without access to air, or anaerobic columns. Part of the energy obtained from biogas utilization is used to maintain the process.

Bacteria convert biomass into biogas at temperatures above 25°C. In countries with hot climates there is no need to heat the metatank.

The process is based on the decomposition (rotting) under the influence of bacteria belonging to two large families of acidogens and methanogens, pre-sorted solid waste (organic waste, thick dirt) in metal containers without air access at an average temperature of about + 55°C. This gas is supplied under pressure to the purification system, and then released into two components - methane and carbon dioxide.

Biogas consists of 55-75% methane and 25-45% carbon dioxide, including small amounts of hydrogen sulfide. The period of formation of high-quality biogas ranges from 7 to 15 days.

The decomposition process occurs in four stages, each of which involves different groups of bacteria.

At the first stage, aerobic bacteria transform high molecular weight organic substances (protein, carbohydrates, fats, cellulose) with the help of enzymes into low molecular weight compounds such as monosaccharides, amino acids, fatty acids and water. This process is called hydrolysis.

Further breakdown is carried out by acid-forming bacteria. This process partially involves anaerobic bacteria, which consume the remaining oxygen and thereby form the anaerobic conditions necessary for methane bacteria. At this stage, the following are produced: acids (acetic, formic, butyric, propionic, nylon and lactic), alcohols and ketones (methanol, ethanol, propanol, butanol, glycerin and acetone), gases (carbon dioxide, carbon, hydrogen sulfide and ammonia). This stage is called the oxidation stage.

After this, acid-forming bacteria create from organic acids the starting products for the formation of methane: acetic acid, carbon dioxide and hydrogen.

The final stage produces methane, carbon dioxide and water. 90% of all methane is produced at this stage, 70% comes from acetic acid. Thus, the formation of acetic acid (that is, the third stage of splitting) is a factor that determines the rate of methane formation.

The production of biogas is economically justified when processing a constant stream of waste, for example on livestock farms.

Russia annually accumulates up to 300 million tons of dry equivalent organic waste: 250 million tons in agricultural production, 50 million tons in the form of household waste. These wastes are the raw material for biogas production. The potential volume of biogas produced annually could be 90 billion cubic meters. m.

Biogas is collected, preventing air pollution, and used as fuel for the production of electricity, heat or steam, or as automobile fuel. Taking into account Russian conditions, methane produced from biogas, or biogas in its main form, can be used as fuel for small boiler houses, vehicles and electricity generation.

The separated methane from biogas is a raw material for the production of many valuable products of the chemical industry - methanol, formaldehyde, acetylene, carbon disulfide, chloroform, hydrocyanic acid, soot.

The remaining high-quality compost and nitrogen-rich fertilizer are sold to agricultural enterprises and individuals.
This technology is considered completely waste-free production, where each component has its own application.

The material was prepared based on information from open sources