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Low cost biogas digester
Parameters to consider in running a biogas digester
The parameters are:
- Acidity - Anaerobic digestion will occur best within a pH range of 6.8 to 8.0.
- Carbon-nitrogen ration (C/N) - a carbon - nitrogen ratio of about 30 - 1 is ideal for the raw material fed into a biogas plant.
- Temperature control - A temperature between 32°C and 35°C has proven most efficient for stable and continuous production of methane. but the action of the digesting bacteria will decrease sharply below 16°C.
- Percentage of solids - Anaerobic digestion of organics will proceed best if the input material consists of roughly 8 % solids. In the case of fresh cow manure, this is the equivalent of dilution with roughly an equal quantity of water.
- Plant design - above or below ground. There are pros and cons with either types.
- Continuous/batch operation - there are pros and cons with either types.
- Stirring - stirring the slurry in a digester is always advantageous, if not essential.
- Gas collection - A non-return valve here is a valuable investment to prevent air being drawn into the digester, which would destroy the activity of the bacteria and provide a potentially explosive mixture inside the drum.
- The level of carbon dioxide and proportion of methane will give valuable information about the state of the fermentation process as well. Infrared sensors are the best means employed today for this purpose. The need for calibration is minimal or nonexistent and the small size, relatively low cost and minimal power consumption make them ideal for this type of application.
Construction of a Hestia biogas digester
A general rule is that the tank needs to be 50 times the size of the
daily input to allow for some space for gas to collect. If your input is
15 gallons of material per day, you’d need a 750-gallon tank.
Hestia biodigesters are approximately 5 by 7 feet wide by 5 feet deep, providing about 700 gallons of capacity. Slurry occupies about 600 gallons of this biodigester; the remaining space is for the gas that’s produced.
There’s an inlet for adding feedstock and an outlet for removing composted slurry.
A closed loop of PEX tubing in the bottom of the tank is plumbed to an on-demand water heater to add heat when the slurry temperature drops below 50°F—the temperature at which cryophilic methanogenic bacteria go dormant and stop producing gas.
If the climate is mild, it may be enough to build a hoop house over the tank to keep the slurry sufficiently warm in winter. Alternatively, the biodigester could be allowed to go dormant during the colder months.
More info: http://energez.blogspot.com/2012/04/video-hestia-home-biogas-plant.html
Hestia biodigesters are approximately 5 by 7 feet wide by 5 feet deep, providing about 700 gallons of capacity. Slurry occupies about 600 gallons of this biodigester; the remaining space is for the gas that’s produced.
There’s an inlet for adding feedstock and an outlet for removing composted slurry.
A closed loop of PEX tubing in the bottom of the tank is plumbed to an on-demand water heater to add heat when the slurry temperature drops below 50°F—the temperature at which cryophilic methanogenic bacteria go dormant and stop producing gas.
If the climate is mild, it may be enough to build a hoop house over the tank to keep the slurry sufficiently warm in winter. Alternatively, the biodigester could be allowed to go dormant during the colder months.
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Biogas digester troubleshooting
Anaerobic organisms require four conditions to produce gas effectively:
Too acidic. Generally if there’s a problem, it’s that the slurry is too acidic (pH below 7). If there is a lot of new, raw, green material placed in the digester or if too much material is added at once, the acid-forming bacteria have a field day. The methane bacteria are so annoyed by the high acid concentration, they simply can’t function. When this occurs, it can take a long time for the methane process to get underway naturally. Low pH is a constant risk and must be countered by plenty of carbon waste, such as leaves and straw, or wood ashes.
If a measured amount of new material—no more than one-fortieth of the total liquid volume of the tank—is added, then the new material has to be dilute enough not to upset the balance. At startup, though, there’s a lack of microorganisms and an inclination toward excessive acidity. Understanding this, we can see why some of the early literature on making methane states that the startup time can be anywhere from three weeks to three months.
I mentioned the acidity problem to a friend with whom I was working at the time. He said, “I make a lot of wine at home. Every once in awhile, I have the same problem. When I do, I add a little baking soda. It straightens out the condition right away.”
The baking soda added to my digester worked like a charm. Within three days, I had methane on the way. This is the secret for keeping your digester sweet and happy. Just add a little at a time until the pH is just right. If the pH keeps dropping, add baking soda periodically until the acid-forming bacteria are no longer producing excessive acid. Don’t be fooled if a lot of gas is produced. The baking soda itself will produce some carbon dioxide.
If the pH gets so low the digester “sours,” it is very difficult to revive and must be pumped out by a septic service and restarted. The Maitreya digester has not experienced this problem.
Too cold. You’ll need to know how hot the tank is, day to day, season to season. To eliminate the guesswork, install sensors both inside and outside the tank. Record these temperatures over a period of time. Then you will know how efficiently the tank is retaining heat, at what rate the temperature drops when no heat is added, and how much energy is needed to raise the temperature. If this is done, then a reliable calculation can be made of how much heat is needed to maintain working temperature if “free” heat is not available. Heat conservation, more than any other factor, determines whether a methane system will “fly” or not.
More info: http://www.homepower.com/articles/home-efficiency/equipment-products/home-cookin-homemade-biogas
- A constant temperature between 95 and 100°F (35 and 38°C). Gas is produced at lower temperatures, but only in very small amounts over an extended period of time.
- The exclusion of oxygen. A septic tank is not designed to keep out oxygen. Granted, some oxygen is excluded by virtue of the water in which the organic matter is transported, but a septic tank is not a sealed system.
- A gentle mixing action. The bacteria that produce methane either have to be transported to their nourishment or their nourishment has to be taken to them. Gentle motion accomplishes this.
- Anaerobic digestion will occur best within a pH range of 6.8 to 8.0. More acidic or basic mixtures will ferment at a lower speed. The introduction of raw material will often lower the pH (make the mixture more acidic). Digestion will stop or slow dramatically until the bacteria have absorbed the acids. A high pH will encourage the production of acidic carbon dioxide to neutralise the mixture again.
Too acidic. Generally if there’s a problem, it’s that the slurry is too acidic (pH below 7). If there is a lot of new, raw, green material placed in the digester or if too much material is added at once, the acid-forming bacteria have a field day. The methane bacteria are so annoyed by the high acid concentration, they simply can’t function. When this occurs, it can take a long time for the methane process to get underway naturally. Low pH is a constant risk and must be countered by plenty of carbon waste, such as leaves and straw, or wood ashes.
If a measured amount of new material—no more than one-fortieth of the total liquid volume of the tank—is added, then the new material has to be dilute enough not to upset the balance. At startup, though, there’s a lack of microorganisms and an inclination toward excessive acidity. Understanding this, we can see why some of the early literature on making methane states that the startup time can be anywhere from three weeks to three months.
I mentioned the acidity problem to a friend with whom I was working at the time. He said, “I make a lot of wine at home. Every once in awhile, I have the same problem. When I do, I add a little baking soda. It straightens out the condition right away.”
The baking soda added to my digester worked like a charm. Within three days, I had methane on the way. This is the secret for keeping your digester sweet and happy. Just add a little at a time until the pH is just right. If the pH keeps dropping, add baking soda periodically until the acid-forming bacteria are no longer producing excessive acid. Don’t be fooled if a lot of gas is produced. The baking soda itself will produce some carbon dioxide.
If the pH gets so low the digester “sours,” it is very difficult to revive and must be pumped out by a septic service and restarted. The Maitreya digester has not experienced this problem.
Too cold. You’ll need to know how hot the tank is, day to day, season to season. To eliminate the guesswork, install sensors both inside and outside the tank. Record these temperatures over a period of time. Then you will know how efficiently the tank is retaining heat, at what rate the temperature drops when no heat is added, and how much energy is needed to raise the temperature. If this is done, then a reliable calculation can be made of how much heat is needed to maintain working temperature if “free” heat is not available. Heat conservation, more than any other factor, determines whether a methane system will “fly” or not.
More info: http://www.homepower.com/articles/home-efficiency/equipment-products/home-cookin-homemade-biogas
Lab scale biogas digester research
Abstract. The effectiveness of cow dung for biogas production was investigated, using a laboratory scale 10L bioreactor working in batch and semi-continuous mode at 53oC. Anaerobic digestion seemed feasible with an organic loading of up to 1.7 kg volatile solids (VS)/L d and an HRT of 10 days during the semi-continuous operation. The averaged cumulative biogas yield and methane content observed was 0.15 L/kg VS added and 47%, respectively. The TS, VS and COD removals amounted to 49%, 47% and 48.5%, respectively. The results of the VS/TS ratio showed very small variation, which denote adequate mixing performance. However there was some evidence of ammonia inhibition probably due to the uncontrolled pH employed. The data obtained establish that cow dung is an effective feedstock for biogas production achieving high cumulative biogas yield with stable performance. The future work will be carried out to study the effect of varying organic loading rate on anaerobic digestion of cow dung in a semi-continuous mode.
Read full paper here: http://www.arpnjournals.com/jeas/research_papers/rp_2012/jeas_0212_635.pdf
Read full paper here: http://www.arpnjournals.com/jeas/research_papers/rp_2012/jeas_0212_635.pdf
4 in 1 biogas digester - piggery + toilet + greenhouse + digester
More info: http://www.ecotippingpoints.org/our-stories/indepth/china-biogas.html
3 in 1 biogas digester - pigsty + latrine + digester
More info: http://www.ecotippingpoints.org/our-stories/indepth/china-biogas.html
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Biogas digester news
http://caagin.blogspot.com/2012/05/assalammulaikum-kengkawan-semlm-bawak.html
http://www.nahrim.gov.my/index.php/ms/pengumuman/587-lawatan-teknikal-meninjau-teknologi-biogas-kelolaan-sp-multitech-renewable-energy-sdn-bhd-oleh-ketua-pengarah-nahrim-pada-16-disember-2013
http://www.spmultitech.com/semenyihbiogasplant.html
http://www.spmultitech.com/qlpajambiogasplant.html
http://www.ukm.my/news/index.php/ms/berita-kampus/766-turning-waste-in-tasik-chini-into-power-.html
http://www.nahrim.gov.my/index.php/ms/pengumuman/587-lawatan-teknikal-meninjau-teknologi-biogas-kelolaan-sp-multitech-renewable-energy-sdn-bhd-oleh-ketua-pengarah-nahrim-pada-16-disember-2013
http://www.spmultitech.com/semenyihbiogasplant.html
http://www.spmultitech.com/qlpajambiogasplant.html
http://www.ukm.my/news/index.php/ms/berita-kampus/766-turning-waste-in-tasik-chini-into-power-.html
4 meter cubic fixed dome biogas digester plant
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| A view of a biogas digester plant |
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| Oulet Pits |
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| Cross section view |
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http://www.paksc.org/pk/biogas-plant-design/965-biogas-plant-photos-from-pdbp
http://www.paksc.org/pk/biogas-plant-design/1080-domestic-fixed-dome-biogas-plant-information-video-punjabi
http://www.paksc.org/pk/biogas-plant-design/1112-success-story-of-aslam-with-biogas-plant
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Biogas digester resources
Resources for biogas digester / methane generator:
- http://takamotobiogas.com/biogas/payg-biogas/
- http://textbook.s-anand.net/ncert/class-xii/biology/10-microbes-in-human-welfare
- http://biogas-technology.blogspot.com/2012/12/biogas-plant-photos.html
- http://bio-gas-plant.blogspot.com/2011/09/biogas-plant-construction-fixed-dome.html
- http://paksc.org/pk/biogas-plant-design/1144-design-construction-and-installation-of-biogas-plant
- http://biogas-technology.blogspot.com/2012/12/biogas-plant-wallpapers.html
- http://biogas-technology.blogspot.com/2013/06/homemade-diy-biogas-plant-digester-step.html
- http://biogas-technology.blogspot.com/2013/10/homemade-medium-size-biogas-plant-for.html
- http://www.homepower.com/articles/home-efficiency/equipment-products/home-cookin-homemade-biogas/page/0/1
- http://hestiahomebiogas.com/gallery-2/
- http://www.ecotippingpoints.org/our-stories/indepth/china-biogas.html
- http://takamotobiogas.com/biogas/how-biogas-works/
- http://paksc.org/pk/biogas-plant-design/item/1014-vacvina-biogas-model-construction-video.html
- http://www.ceres.org.au/greentech/Projects/Energy/howitworks.html
- http://www.habmigern2003.info/biogas/methane-digester.html
Biogas digester types
The two main digester types of digesters are the continuous and the
batch.
Continuous digesters have a constant throughput of material, and
Batch digesters extract the gas from a contained batch of material, which is then emptied and a new batch added.
Want to construct your own biogas biodigester? Click here!
Continuous digesters have a constant throughput of material, and
Batch digesters extract the gas from a contained batch of material, which is then emptied and a new batch added.
Want to construct your own biogas biodigester? Click here!
biogas digester system or components
The biogas digester is the system component where the
animal, human and other organic wastes are introduced, usually as a
slurry with water, to break down anaerobically.
A storage container is used to hold the gas produced, from which it is piped for burning as a fuel. Variable volume storage (i.e. flexible bag or floating drum) is easier, cheaper and more energy efficient than high pressure cylinders, regulators or compressors.
When the digester is emptied, the spent effluent is dried for later reuse as a fertilizer.
A storage container is used to hold the gas produced, from which it is piped for burning as a fuel. Variable volume storage (i.e. flexible bag or floating drum) is easier, cheaper and more energy efficient than high pressure cylinders, regulators or compressors.
When the digester is emptied, the spent effluent is dried for later reuse as a fertilizer.
Microbes in biogas digester
Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel. You have learnt that microbes produce different types of gaseous end-products during growth and metabolism. The type of the gas produced depends upon the microbes and the organic substrates they utilise. In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO2.
However, certain bacteria,which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Do you think we, human beings, are able to digest the celluose present in our foods? Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas.
The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertiliser. Cattle dung is available in large uantities in rural areas where cattle are used for a variety of purposes. So biogas plants are more after build in rural areas. The biogas thus produced is used for cooking and lighting.
However, certain bacteria,which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Do you think we, human beings, are able to digest the celluose present in our foods? Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas.
The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertiliser. Cattle dung is available in large uantities in rural areas where cattle are used for a variety of purposes. So biogas plants are more after build in rural areas. The biogas thus produced is used for cooking and lighting.
Biogas digester energy
Each kilogram of biodegradable material yields around 0.4 m³ (400l) of gas.
So
in practice, in small scale waste to energy systems, if you have some
livestock, plus kitchen and human waste you can meet your cooking and
lighting needs easily:
• 2 gas rings for a couple of hours a day will use between 1-2 m³
• Gas lights need around 0.1 m3 (100l) per hour.
Driving any kind of engine (eg a generator or a pump) is, however, way beyond the domestic-scale. (Better to go for
algal biodiesel!)
Biogas digester disadvantages
Most practical to be generated and used at the source of the waste.
This is because the energy needed to compress the gas for transport, or
convert it into electricity is excessive, reducing the efficiency of
biogas energy production.
For safety, basic precautions (see below) must be adhered to.
Biogas digester advantages
Makes good use of organic wastes. You can obtain fuel from sewage
sludge and animal slurries first, and prevent runoff and methane
emissions at the same time – and you still get fertiliser at the end of
the process.
Is a clean, easily controlled source of renewable energy.
Uses up methane, a powerful greenhouse gas.
Reduces pathogen (disease agent) levels in the waste.
Residue provides valuable organic fertilizer.
Simple to build and operate.
Low maintenance requirements.
Can be efficiently used to run cooking, heating, gas lighting, absorption refrigerators and gas powered engines.
No smell (unless there’s a leak, which you’d want to know about and fix immediately anyway!).
Is a clean, easily controlled source of renewable energy.
Uses up methane, a powerful greenhouse gas.
Reduces pathogen (disease agent) levels in the waste.
Residue provides valuable organic fertilizer.
Simple to build and operate.
Low maintenance requirements.
Can be efficiently used to run cooking, heating, gas lighting, absorption refrigerators and gas powered engines.
No smell (unless there’s a leak, which you’d want to know about and fix immediately anyway!).
Biogas digester temperature
How long you leave the material in a batch digester depends on
temperature (2 weeks at 50°C up to 2 months at 15°C).
The average is
around 1 month – so gauge how much material you will add each day, and
multiply it by 30 to calculate the size of the digester.
While
anaerobic digestion occurs between 32° F (0°C) and 150° F (65°C), the
optimum temperature range for methane generating microbial activity is
85°F (29°C) to 95° F (35°C).
Little gas production occurs below
60°F (16°C).
In colder climates placing the digester in a greenhouse,
and perhaps using some of the methane to warm the system, are possible
strategies.
Biogas digester size
If generating methane from manure, collect dung for several days to
determine average daily dung production.
On this basis, the appropriate
size biogas digester plant can be calculated.
For example, where
55 kg of dung a day is available a 8 m3 plant is warranted; where it’s
only 6 kg of dung a day, a 1 m3 plant will suffice.
For a family of 8 with a few animals (say 8-10 cows), a 10m³ digester is a commonly used size in India, with 2 m³ gas storage.
What Is Biogas
Biogas is a gas mixture which is generated when organic compounds are
fermented in the absence of air (anaerobic fermentation). This gas
mixture is mainly made of carbon dioxide (CO2) and methane (CH4).
Methane is a combustible gas, which means it can be burned. It can be
used as a fuel for cooking and lighting.
The precautions:
The precautions:
-
The plant must be tested to make sure it is water-tight and gas-tight.
-
Enough fresh material must be added before it is used every day.
-
There must be a water source to provide enough water to clean the livestock pens regularly, to provide fresh material for the fermentation chamber system. (Each liter of manure needs 1 - 3 liters of water).
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The plant must be equipped with a safety valve or U-shaped barometer.
-
Chemicals such as detergents or pesticides must not be put into the fermentation chamber.
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Initially, after fresh manure and water is added to the fermentation chamber, the valve should be opened so the gas can escape. At this stage, the gas is mainly carbon dioxide. This should be done once or twice, before the biogas plant comes into use for biogas production.
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The gas from the fermentation chamber is not used directly, but is stored in an auxiliary gas tank protected by a safety valve. It is this auxiliary gas tank, not the main gas tank, which is connected to any domestic appliances.
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DIY Biogas: Make and Use Your Own Renewable Natural Gas
Make your own homemade natural gas from food scraps, garden trimmings, and animal waste!
Understand how to craft a recipe to make your own renewable energy substitute for natural gas and propane.
DIY Biogas contains complete plans and parts lists with active links to build two different biogas generators that help you learn, understand, and grow your biogas operation. With this hands-on, minds-on guide, you’ll gain the knowledge and experience you need to convert waste into energy. Whether you’re looking for a unique science project or want to cook meals with your own backyard biogas, this book is the most practical place to start.
With fuel prices and scarcity on the rise, it’s time to re-learn how to meet our own energy needs. Start today and harvest your own local, renewable energy resource tomorrow!
Understand how to craft a recipe to make your own renewable energy substitute for natural gas and propane.
DIY Biogas contains complete plans and parts lists with active links to build two different biogas generators that help you learn, understand, and grow your biogas operation. With this hands-on, minds-on guide, you’ll gain the knowledge and experience you need to convert waste into energy. Whether you’re looking for a unique science project or want to cook meals with your own backyard biogas, this book is the most practical place to start.
With fuel prices and scarcity on the rise, it’s time to re-learn how to meet our own energy needs. Start today and harvest your own local, renewable energy resource tomorrow!
