In our three part series we have examined the use of biogas to reduce emissions and drawdown carbon as a tool to address climate change. We looked at some of the factors that make biogas suitable and some of the limitations that might make biogas less than optimal for a specific location or application in the first article, and biogas through the lens of the permaculture principles in the second article.
In this last article, we will examine some of the types of small scale biogas, and what applications they may be useful for. Included are links to the systems location and service or equipment providers.
There are three main kind of biogas digesters
1) Buried or sealed vault, popular in China, fairly expensive, requires skills to make, and takes time, but if built properly will last forever. These are primarily for animal based systems, especially pig and cattle manure.
2) Tank system, which functions like a vault, except the anaerobic conditions are created by the use of a sealed container of some kind. Water tanks and second hand Industrial Bulk Containers (IBC’s) are used for this. These are primarily food waste systems
3) Bag systems, which are very easy to make, very inexpensive, but relatively fragile (though there are exceptions to that, such as the Sistema Biobolsa, covered below). These are primarily animal waste systems.
4) Floating gas systems, which are easiest to make, but some have issues of a percentage of methane escaping to the atmosphere, which is counter productive to reduce the effects of climate change. Methane is much more powerful as a green house gas than carbon dioxide. Floating gas systems can be for food waste or for animal based systems, depending on size.
Below are some examples of systems that we have either seen or are aware of as being proven technologies.
Buried Vault, Monkey Bay Wildlife Sanctuary, Belize
Matthew Miller and Marga Waals Miller run a guest house and environmental education centre in Belize called Monkey Bay Wildlife Sanctuary, a 1000 acre nature reserve that has three different ecosystems on it, broadleaf forest, riparian zone and savannah.
In 1994, there was a joint project between the German Appropriate Technology Exchange and Belize’s Ministry of Agriculture, targeting pig and cattle farms for underground masonry domes, or vault systems. Working with the German technician, Matthew and their technician modified the design to accept mostly humanure. With the volume of students Matthew has had it has been sufficient to run the kitchen two days a week. The balance of time they use natural gas.
The vault design is similar to Chinese vault designs. This is a proven technology that is scalable. If you need more gas, you make a larger vault, and provide more feedstock. A good analysis of feed stock potential is critical when designing this system.
It took a month to build. As Matthew explained: “One week to hand dig the foundation earthworks. Two weeks to complete the cement casting, block work and plastering. Each row of blocks laid to construct the underground digester, a day of drying time needed. And one week to complete the latrine building, plumbing and inoculating the digester with water and biogas sludge from Central Farm. It’s been in continuous operation for 26 years.”
The toilets are nice and clean and feed into the vault through the collecting trough. The effluent is removed and used as fertilizer.
The system cost about USD2500 to build, which is not a lot for the large volume it can handle, ten cubic meters. Half of that was on material, and half on labour.
Robust system. Depending on size, can handle large volumes of waste. Well suited to institutional situations and for medium or larger animal husbandry operations.
Needs skilled labor to build. Needs steady supply of animal waste or human faeces to be used daily. High upfront cost.
Plastic Bag & Improved Bag System, Guatemala
Pedro Mancillo is a cattle farmer in the Peten, Guatemala, and a friend of one of our former Permaculture Design Course Graduates, Andrew Puente. He has had two bag systems. The original bag system, which was expected to last three years, only lasted one year because a root grew through the bottom of the bag. It was a good learning system for Pedro, and he decided to get a better system. This is one of the reasons we did not decide to build a plastic bag system for our piggery as we felt it would be too delicate.
After his original plant failed, Pedro was able to purchase a Geomembrana system from a local dealer in Guatemala. His improved system is expected to last 20 years.
Pedro has a medium sized dairy farm and feeds his biogas plant with cattle manure and whey from making cheese. That system can provide up to 13 hours of cooking, and a whopping 145 gallons of high value fertiliser, per day at full capacity.
Both systems are relatively inexpensive. Bag systems are an excellent choice for animal husbandry, turning what might be a pollutant into the resources of biogas and fertiliser.
Fragile. The first system failed within one year, but the second system is expected to last 20 years.
The Biobalsa bag biogas digesters in these photos were installed in Guatemala by a Guatemalan renewable energy company, Negawatt Ahorro Energetico, who is the agent for Biobolsa in Guatemala. An example of their work can be found, here.
Sistema.bio is a biogas digester company in Mexico. Biobolsa was established around 10 years ago. In that time they have installed 17,000 systems, providing 104,000 people with clean burning biogas, and treated 13M tonnes of animal waste. They have offices in other countries, Colombia, Kenya, India, and a distributor in Guatemala. They are both a business and a social enterprise working to assist people in obtaining biogas and bioslurry from dung. I am genuinely impressed with their company and their biodigester has a solid reputation.
Their biogas plant is a very sturdy bag system which is low cost and simple to install. It is a larger system and designed for farms, especially pig and cattle farms, and has an expected life span of 30 years.
The Biobolsa’s digester is a large bladder made of HDPE, which is fed through one side with a mixture of animal waste and water, and where the retention time between feeding it, and the effluent coming out, is long enough for the feedstock to break down. A simple hole with the dimensions of the reactor is required from the customer to install and commission the system. No particular skills are needed to use and maintain daily the plant, the system is very simple and easy to understand for farmers. The components are common and can easily be found in any hardware store. The system is very low tech.
They do not merely sell systems. They provide training and finances through their 6 step program:
1. Demonstration event, to show stakeholders how the Biobolsa works and how to manage a biogas system.
2. On-site diagnostic and financing plan, to site the plant, look at nutrient flows, and derive payment plans
3. Manufacturing, they make the plant, provide the stove and equipment needed to use the biogas.
4. Installation, where they help the people install their system
5. Service and monitoring, after they install the system the relationship continues to assist in developing the skill set to maintain the system
6. Their sixth step is that they have happy clients.
Can handle large amounts of manure. Relatively cheap. Long life expectancy. Stellar pre-purchase stakeholder engagement and post-purchase support. Credit available. The system is scalable, and if you had as little as 30 litres of manure a day, from three cows or ten pigs, they can design a system for you.
Floating Gas System, Dem Dats Doin, Belize
The very first biogas system I saw was in 1988 when I walked over to visit Yvonne and Alfredo Villoria at Dem Dats Doin (Them That’s Doing), a homestead they established in the early 1980s located about a mile from the village of San Pedro Columbia, Toledo District, Belize, where I live.
Dem Dats Doin are pioneers in sustainability. They had several firsts for me. The first photovoltaic system and the very first biogas system I ever saw was at Dem Dats Doin.
Their system was fed with pig manure and humanure. Dem Dats Doin has a 14m floating dome biogas digester that provides much of their cooking. This is a proven design that has been used widely in China and India.
Labour costs approx. $2500 bz. The digester is 14m3, and the gas holder is 2m3. The gas goes to their kitchen. The effluent goes to their plants.
Dem Dats Doin is a botanical garden of various species, and Yvonne and Alfredo are soon retiring. The farm is up for sale! You can contact them through email or through their web site.
Relatively low cost. Long lasting.
Like most floating drum systems, some gas escapes from the side of the digester and does not end up in the gas storage. The metal drum rusted and was replaced. More suitable for farms that engage in animal husbandry.
(Photos courtesy of Dem Dats Doing)
Home Biogas, Examples From Guatemala & Belize
Home Biogas is a company from Israel that makes small scale portable biogas plants. The systems are designed for people who are not interested in building their own. These are a “no hassle” system. As they say “Everything you need comes in the box”. One simply unloads the box, sets up the components, feeds the biogas plant with manure, water and their inoculant, and waits till the biogas plant produces gas. The stove is included. This is a good system for people who do not have time to build one, or who prefer just to buy one and get it going.
This bag digester is designed for use with food waste, but it can accept up to %70 manure. A low flush marine toilet is an option, which makes feeding humanure into the biogas plant as simple as flushing the toilet. This helps for people who do not want to deal with human faeces.
The system packs in one cardboard box, which can be lifted by one person.
There are two models:
1) Home Biogas 2, which is a small bag system can generate up to two hours of biogas per day, which sells for USD720. There is a video of that, here.
2) Home Biogas 7.0, which can holds 4000 liters of slurry and can hold 2500 liters of gas. This system is designed for a small farm. It is estimated this digester could provide up to 6 hours of fuel a day.
Relatively low cost, can be dismantled and moved very easily, prepackaged, easy assembly. Small foot print.
(Photos courtesy fo Home Biogas)
ARTI Biogas System, India
This is a biogas plant designed in India by Appropriate Rural Technology Institute. It is a floating dome model designed for use with food scraps and limited uses of manure, and suitable for urban dwellers or people who do not have access to cow dung.
Advantages of the ARTI digester are its small foot print, and ability to use vegetable byproducts ranging from banana rhizomes, leftovers, spoiled flour and other food wastes. It is not difficult to build, and multiple open source designs can be found, for example on the “Build a Biogas Plant” web site here, and a pdf version, which can be found, here.
This is a proven design that has been in use for decades, with thousands of such systems having been built. While they originated in India, there are ARTI biogas systems in use in Africa. It is estimated that 2000 ARTI biogas digesters have been built.
Relatively easy to build, small footprint, proven model. Ideal for urban situations, and can be placed on a balcony, terrace or in the backyard.
Water tanks are expensive
Solar CITIES, MMRF
The system we run at Maya Mountain Research Farm is the Solar CITIES biogas plant. The design is from Dr. Thomas Culhane, and is made from IBCs (Industrial Bulk Containers). The system is a hybrid of a floating gas system and a sealed vault system. Because IBCs are now ubiquitous to the planet, this digester is very inexpensive to build.
IBCs are fairly common in Belize and are used for one way transportation of liquids. Here in Belize they are often used to bring in feed for aquaculture, and then discarded. IBCs used for agrochemicals are not suited for the biogas digester, as the biocide residue would be damaging to the methanogenic bacteria, but could be used for the biogas storage. We did not have to use any IBCs that had biocide in their life cycle, having found three containers that brought fish feed into the country.
Three IBCs are used to make the Solar CITIES biogas plant. One IBC is the sealed bio-digester, like a vault, where the methanogenic bacteria break down the feedstock. This is kept air tight and has three holes at the top. One hole is for the inlet of feed stock, which goes in on a 3 inch pipe, another is for the gas, which comes out of the top of the tank and is connected by a hose to the gas storage, and the third pipe is for the effluent, or spent feed stock, coming out on a two inch pipe, which is collected and used for fertilisers.
The digester has to be painted black to avoid issues tied to the growth of algae, some of which will stop the anaerobic digestion. The feed stock for this kind of digester is mostly food waste and byproducts of food processing. We use banana peels and banana, citrus skins, coconut whey from making oil, ground partially defatted coconut meat, bruised avocado, breadfruit, jackfruit pulp, limited amounts of chicken and humanure.
The other two IBCs are broken down and reassembled to make the floating gas storage unit. This involves cutting the top off of one tank, and the top of the other, and turning it sideways. The top piece floats in the water in the bottom container, and the gas is stored in the top container. It is easy to see how much gas is available, and no gas can leak out the side, unless the tank is overfull If the top is low, we have little gas. If it is high, we have gas available.
Weight is applied to the top of the gas storage to create pressure to send gas to the stove. We use cement blocks or stones.
To increase gas production, an additional digester could be piped in parallel.
Assembled from commonly available recycled materials. Relatively low cost. Small foot print.
Limited capacity. IBC plastic may photo-degrade if left exposed to sunlight. Average production is 1.5 hours of cooking per day.
Solar CITIES Biogas/Aeroponics System, New York, USA
Kathy Puffer is a permaculture teacher, a mom, an urban farmer, and an advocate for biogas. She has installed many systems in the US, Haiti and our system in Belize. She is a great teacher and a fantastic coworker. Our system was made possible through her.
Kathy and her husband Ed Puffer have their Solar CITIES biogas plant in upstate NY. Their soils are very poor, and winters can be cold. They installed a two IBC digester system in the basement, where temperatures remain warm. It was inoculated with horse manure.
They feed their biogas digester through their kitchen sink, and get enough gas to provide almost all of their cooking needs. In many respects, except for its location and the twin tank digesters, it is very similar to hundreds of other Solar CITIES IBC digesters.
However, Kathy diverges widely from most other systems with her effluent management. Kathy has harnessed her biogas effluent to run through an aeroponics system. Similar to a hydroponics system, the nutrient rich slurry that leaves the plant is cycled through a series of beds and towers so that the roots of the vegetables and herbs can access the nutrients as they pass through the system.
Kathy and Ed raise poultry and goats, raise bees, and grow a wide variety of herbs and vegetables at Hudson Valley Vertical Farms. All of their basil, lettuce, tomato, parsley, beans, spinach, Swiss chard, and bok choy come through their aeroponics system.
Her work combining aeroponics and biogas is cutting edge work and practice.
Simple system. Proven. Low cost. Small footprint. NOW! With added benefit of food production!
Not much to say against this system. Grow towers add more expense.
Biogas has a place in the permaculture toolkit. The topic is vast and there is a lot of work that has been done in the field, and even more opportunities for the future. The scope of these articles is too small to provide a comprehensive analysis of the technology, but I hope it has provided tools for those of you who may want to delve into the topic in more depth.
There are a wide range of choices available, to suit a wide range of needs and opportunities. Channeling the nutrient and energy flows through our farms, kitchens and communities to extract more resources is going to become very important in the coming years. The application depends on the situation. Biogas plants provide clean burning fuel as an alternative to burning biomass, an alternative way to compost and high quality fertilizer, and help to drawdown carbon.
As I end this article and close this series, here are a few prepackaged systems that are available. Thank you for taking the time to read this.
Commercially Available Systems
Biobowser of Australia makes tank digesters that function as above ground vaults. Their design looks robust.
SIMGAS, B.V. of the Netherlands makes biogas vault systems and primarily targets Africa and Asia. Their vaults are made from a dense plastic and are modular, so they can build systems to meet their clients needs. They include an option to pipe a toilet directly to the digester. One advantage of their system over a traditional vault is that the installation time can be as little as one day.
Flexi-biogas of Kenya makes bag systems for sale of various sizes for livestock, as well as a “Bio Sans” system, which takes humanure from toilets to make biogas.
Biotech Renewable Energy, of India which makes preassembled floating dome models of different sizes, designed for food waste.
Future Resource Development of India makes different flowing dome models ranging in size from 10-120 litres. They claim the 10 litre model will produce usable fuel for 1.5 hours. The 120 litre system is said to have the capacity to produce fuel for 6.5-7.5 hours per day. These systems are primarily for food waste. They also make commercial systems up to 600 litres.
Puxin of China makes biogas plants ranging from family sized suitable for disposing of food waste, to larger systems designed to accommodate industrial farm waste. They make many types and sizes of biogas digesters, from smaller food waste models to large scale animal waste models.
Green Energy Huamei, Ltd, of Hong Kong makes various sizes of bag systems, and also sells stoves, water heaters and rice cookers for biogas.
Biogas Consulting, SA of South Africa installs Puxin digesters on site for their clients. The company sells stoves and hot water heaters for biogas. They also produce bag systems in South Africa, primarily for animal waste.