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Biogas and Carbon Farming – Part 1

Why we went for biogas

Maya Mountain Research Farm is a permaculture project in the foothills of the Maya Mountains in southern Belize. It was founded on degraded citrus and cattle land in 1988. Our primary focus is on multistrata agroforestry systems for food security, reversal of land degradation and carbon drawdown. Biogas neatly overlaps with much of our end goals.

The question of bio gas in permaculture has come up many times over the years. Biogas in the right application can be an embodiment of the principles of permaculture, but, like most things in permaculture, the answer to the question of wether biogas is realistic or not for a specific location or application is best prefaced with the two words, “It depends”.

We live two miles from the nearest road, on a river only navigable by dug out canoe. Hauling heavy tanks of propane in and out was not an attractive option. But biogas was.

Biogas is comprised of combustible gases, mostly methane and carbon dioxide. Biogas is the product of anaerobic decomposition of biological waste material. That waste can be manure, food scraps, it can be byproducts of food processing, like whey or gleanings, or pressed seed cake from making oil. To make the biogas you need an environment that is closed to oxygen. To do that, you need to make a biogas plant, where biomass and water can be combined, and oxygen excluded. You will need to establish a community of methanogens, which are the microorganisms that create methane. Many digesters use cow manure to establish the methanogenic community, but methanogens can be obtained through using layers of “muck’ found in ponds or slow moving water. The breaking down of the biomass without oxygen is called “anaerobic “ Once established, a biogas plant can effectively deal with waste disposal and create high value fertilisers, while also creating methane as fuel.

Biogas can be a valuable tool for climate change mitigation. If widely dispersed, biogas has the potential to avoid the equivalent of 4.65–9.7 gigatons of annual carbon emissions. Although biogas can be used to generate electricity, for transportation or for lighting, for the purpose of this article, we are discussing biogas as fuel for cooking.

Worldwide there are an estimated 400 million biogas plants. India, Israel and China are hotbeds of biogas innovation, and have been leading research and development of biogas. A follow up article to this will look at the various biogas systems available, ranging from prefabricated to designed for a specific site.

Biogas is not a universal application. The questions that are important to ask when considering biogas would be about the location, the need, and the available resources. Biogas can be suitable for many applications, ranging from urban to semi urban, to rural, to areas without access to fuel wood. Careful observation and analysis of what nutrient cycle you might tap into to obtain your feedstock, and where would you apply the effluent will lead to an informed decision on the choice of biogas for your situation. In areas of extreme cold, care must be taken to maintain enough warmth for the methanogens to thrive.

We raised pigs from perennial crops for seven years. We had a significant amount of manure. A biogas plant looked attractive, and we looked into a biogas plant, but never got around to it. The interest in biogas remained. At the time we were creating a lot of biochar while cooking to feed the pigs. A link to an article about that can be found, here.

We looked at various designs, buried vaults, horizontal poly bags filled with water and manure, prepackaged systems, floating gas collectors in slurry, to batch digesters made from 55 gallon drums. An overview of these systems will be in a follow up article. All of these were either too expensive for us, at the time, or did not seem robust enough for our needs.

Kathy Puffer, is a biogas teacher/installer at Solar CITIES, the leading sources of biogas education in North America. Over months of writing and looking at possibilities and opportunities for biogas, we arranged to have a course on biogas here at Maya Mountain Research Farm, and build a Solar Cities biogas plant.

We held a fundraiser for the components we would need, some second hand IBCs, some piping, to bring Kathy to Belize, and to cover the cost of providing scholarships for Belizeans. We raised $1600 of the $1300 in costs. The surplus went to solar cookers for our former students. We obtained support from many people, friends, former students, Belizeans at home and abroad, and supporters of Solar CITIES. We are grateful to every person who made this happen.

IBC Delivery
Delivery of the three IBCs for the biogas digester and the gas storage.
Image provided by author.

With Kathys guidance, we built our solar CITIES biogas plant using three recycled IBCs, one for gas generation and a clever floating gas storage system built from the remaining two IBCs. They were otherwise garbage, and we were able to find a use for them. This was a five day course and finished on the 18th of April, 2019. The components cost about USD450, all told, and from it we get 1-2.5 hours of biogas per day, and a bucket of fertilizer, which we apply to plants close to the house.

Preparing the digester
Preparing the digester.
Image by author

We charged the system with 100lbs of cow manure. The manure has methanogenic bacteria, that can eat chewed grass, or any starch or fat. While the manure is long gone, the effluent that comes out of the system still smells of cow manure, over a year later.

 

The Solar CITIES biogas plant can receive up to 30% manure, but this biogas plant is best used for food waste, which has more embodied energy than manure. The plant is a small plant, and manure takes longer to break down than food waste. To obtain equal amounts of biogas from pig, cattle or poultry waste we would need a much larger system, have a lot more feedstock and have to raise a lot more animals than we do, now. Because of our rural location and ability to raise animals, this is possible, but a system designed to run off of food waste and byproducts of food processing was a better fit as we have plenty of surplus food and less than 100 ducks and chickens and less than 10 rabbits.

As an element in a larger system, the biogas plant functions very well. Placed close to the kitchen, by the rabbits, between the poultry system and the kitchen, we visit this location a few times a day to load it with food waste, scraps we grind in our blender, a few minutes to carry away the effluent which is a fertiliser, and to turn the valves on and off to send fuel to the kitchen. it has become an enjoyable part of our daily routines, and we use it everyday. It took us about one month before we had usable gas. Since then, we have not had to add any cow manure.

Building the digester
Building the digester
Image by author

Our system decomposes food waste that we would otherwise compost. We have a very mature multistrata agroforestry system, over 30 years old, with an emphasis on tropical staple trees, such as banana/plantain, coconut, breadnut, breadfruit, avocado, jackfruit, peach palm and others. We have huge amounts of surplus. We sell some, we use some as animal feed for our poultry and rabbits, and we donate food to an elderly feeding program in nearby Punta Gorda Town.

Often we have more food than can be used. I picked up a bucket of avocados this morning. How much guacamole can we eat? Not enough to keep up! Happily, our biogas plant loves avocado peels, avocados and over ripe bananas, as well as mulberry leaves, cassava peelings, moringa leaves, mango and pineapple peels, pressed coconut seed cake, peach palm fruit, breadfruit skins and overripe fruit, a little bit of humanure and the occasional scoop of rabbit manure. We get 1-2.5 hours of biogas per day from our biogas plant, and a bucket of fertiliser, which we apply to plants close to the house.

Storing Gas
Storing Gas.
Image by author

In addition to biogas, we have multiple elements providing the function of cooking, a wood burning cookstove, a cob pizza oven, a biochar kiln, and an open fire hearth (which make the best corn tortillas). These all burn dried biomass, like wood, coconut husks, cahune palm seeds, rice hulls and bamboo to make heat. We live in a rural area, heavily focusing our work on trees. We have plenty of wood for fuel. When its sunny, we can also use our solar box cooker, or our parabolic solar cooker.

Some days I wake up and cannot be bothered to make a fire. I like making our morning coffee on the biogas plant.

A legitimate concern is that a small biogas plant produces insufficient gas to be a primary source of cooking energy. A limitation of the present system is the amount of gas we can obtain from one IBC daily. To solve this, we are considering adding a second digester to feed the single storage unit, which would effectively double our daily amount of available biogas from 1-2.5 hours per day, to 2-5 hours of available gas, per day. That would meet all of our needs, except for baking.

Cooking on Gas
Cooking on biogas.
Image by author.

We have not decided to expand the system yet. Doing so would require more attention to the system, more management, and more feedstock, but it is an option for us to explore.

Biogas is a useful element in our farm, providing us with clean burning fuel, disposing of surplus food, fruit that may have fruit fly larvae and food scraps that have limited value, and creating high value fertiliser.

In follow up articles, we will look at various biogas plant designs, with pros and cons, and biogas through the lens of permaculture principles.

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Christopher Nesbitt

Christopher Nesbitt has run the Maya Mountain Research Farm, an ongoing permaculture project in southern Belize, Central America, since 1988. Former degraded citrus and cattle land, the farm is focused on the intersection of agriculture and ecology. He managed the Toledo Cacao Growers Association in cooperation with UK based Green & Blacks from 1997 to 2004. Since 2004, the Farm has been working on specific ways to draw down carbon, with an emphasis on food security, degraded land repair, multistrata agroforestry systems and staple tree crops. The work done at MMRF clicks off on all 17 of the Sustainable Development Goals. In 2019, the farm won the Commonwealth Secretary Generals Innovation for Sustainable Development Award under the Prosperity category. Christopher runs the farm with his wife, Celini Logan Nesbitt

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