6 reasons to use a biodigester as a low tech, off the grid, renewable energy source for cooking

6 reasons to use a biodigester as a low tech, off the grid, renewable energy source for cooking

By Nico, Apprentice 2020

“Agricultural, industrial, and human digestion processes create an ongoing (and growing) stream of organic refuse. Without thoughtful management, organic wastes can emit fugitive methane gases as they decompose. Methane creates a warming effect 34 times stronger than carbon dioxide over one hundred years.” - Project Drawdown

Renewable Energy for Cooking

For almost two decades now, Rancho Mastatal has been working on creating a more sustainable lifestyle by researching, developing, and teaching about more efficient ways to build, grow food, cook, and live as a community while reducing the impact these activities have on our environment.

As cooking is one of the most energy-consuming activities within a house, we find it relevant to implement an alternative renewable energy source to satisfy one of our guests’ favorite moments of the day: meals. With that perspective, we built a biodigestor 8 years ago.

What is a Biodigestor?

Our biodigestor

A biodigestor is basically a system that allows us to produce methane out of human and animal manure (see more info on last year’s article). Here at the Ranch we decided to go for a low tech, polyethylene tubular biodigester technology, also known as the sausage system here in Costa Rica, because of the shape of the chamber. We chose this because it is a cheap and simple way to produce methane for small-scale farmers. It is appealing to rural people, firstly because of the low cost of the installation and therefore of the gas, and also for the improvement in the environment that the installation allows. It can be applied in rural or urban areas and in both low and hilly lands, creating a low tech system able to produce a renewable energy source as well as a fertilizer for your land.  

A glance at our system

6 Reasons to Build a Biodigestor

But besides the awesome concept of being able to transform waste into energy, there are many other advantages to having a biodigestor. Here are 6 reasons on why you should build one:  

1. Biodigestors can be Low Tech

A common misconception about biodigestors is that they should be these high tech, expensive systems made out of a lot of different components. Like people, biodigestors come in many shapes and sizes: from continuously fed to batch fed, made out of metal or polyethylene, vertical or horizontal, using cow manure or human waste (or both), there is probably a biodigestor out there waiting for you. If you decide to go for a simple system like ours, there aren’t many components and you would be surprised by their simplicity. With the help of a couple people and some skills, you can set your system up within two days. The maintenance is pretty simple as well, and again, depending on the system you choose, you can decide to either dedicate a bit of time for maintenance every day, or choose a batch fed system, which takes more time to put in place but is then autonomous for a couple weeks

2. Biodigestors can be cheap

Again, this depends on a lot of variables: which system you choose, whether you have to excavate soil, if you are willing to do it yourself or prefer hiring people, whether you are able to use reused materials, etc. For instance, the main component of our system, which acts as a fermentation chamber and a gas reservoir, cost us $700.

3. It can be used off-grid

Here at the Ranch, the amount of people coming through doesn’t allow us to be completely off the grid; we cook over 23,000 meals a year! We still decided to implement this system in an effort to reduce our dependence upon fossil fuels such as propane and take a step toward ecological self-sufficiency. For smaller communities, like a small scale farm, or by increasing the size of the system, it is totally possible to implement an off the grid cooking system.

The methane stove that we cook meals on

4. It creates a nutrient rich organic fertilizer

This low tech system houses a wide variety of bacteria, each one with a specific task. Some break the matter into simpler molecules of sugars and acids. Other microbes, which find oxygen toxic, are able to break down the simple organic matter to form gases. The ultimate end result of this process is both the natural gas for heat and electricity as well as valuable soil amendments which we disperse throughout our gardens.

5. It reduces the greenhouse effect

Methane, CH4, which makes up 70% of the biogas produced by our biodigester, creates a warming effect 34 times stronger than carbon dioxide. By burning this gas, not only do we create a renewable energy source that allows us to produce energy, we decompose the methane into a less potent greenhouse gas.

6. It’s comfortable

Some people are apprehensive about the idea of having to use a composting toilet ( even though they shouldn’t be, see article by Moanna on Composting Toilets to discover all the wonders of using a composting toilet, a wonderful low tech and off the grid system). By connecting your greywater system to a biodigestor, you will keep the comfort of doing your doodies in a water system while doing your duties for our wonderful Earth. As a matter of fact, our biodigster’s toilet was voted the Best Compost Loo In The World Award in 2012 by the readers of Permaculture Magazine, Inspiration for Sustainable Living.

Why else are Biodigestors Great!

The list doesn’t stop here. A biodigester helps reduce landfill and water-polluting effluents, and eradicates odors and pathogens. It allows small scale farming to create a renewable energy source while allowing them to better control the breaking down of their animal manure into fertilizer, being more self-sufficient and less dependent upon other chemicals. In a world where it has become increasingly urgent to find simple solutions to step towards sustainability, implementing low tech and easy to manage solutions like this one seems more relevant than ever.

The Project Drawdown, a comprehensive plan to combating climate change, puts Biodigestors in the top 100 things we can do.

Hope you feel inspired to think about and make changes to the current system of waste management.

Check out Moanna’s latest article on why composting toilets are another great way to make a sustainable change in the system.

The Biodigester

The Biodigester

By Mike Paladino, 2019 Rancho Mastatal Apprentice

It's 5.30 am in the dewy morning rainforest of Mastatal – the cacophony of squawks and birdsong remind us that the winged beings have begun their daily business of foraging for themselves and their young, the toads have tucked themselves into the nook of a tree or within a pile of leaves to avoid the relentless heat of the new day, and one by one the guests at Rancho Mastatal stretch and yawn their way out of their abodes and ease their way towards their first cup of coffee. Within moments of a couple of team members arriving, one opens a valve on a stove and WHOOSH! sparks the flame upon which we will cook our breakfast. But the source for this gas isn't of your average origin. This fuel comes from one of the most potentially troublesome yet profoundly utile resources on Earth: poo.

Here at the Ranch we are utilizing two means of generating alternative energy known as “biodigesters.” A biodigester houses various bacterial species to break down organic matter and capture biogas (namely, methane) released by the bacteria in a process called anaerobic fermentation – i.e. the organic matter is digested by the microbes in the absence of oxygen. In the particular case of Rancho Mastatal and many other sustainability centres around the globe, the common organic matter for these microscopic busybodies is excrement, primarily bovine with a smaller source coming from yours truly. There are several kinds of microbes at work here. Some break the matter into simpler molecules of sugars and acids. Other microbes, which find oxygen toxic, are able to break down the simple organic matter to form gases. The ultimate end result of this process is both energy for heat and electricity as well as valuable soil amendments which we disperse throughout our gardens. Essentially all of our breakfasts (roughly 30% of all food cooked here) are prepared solely with the captured methane gas from the combined two mechanism. It is estimated that reliance upon propane as our major cooking gas was cut by roughly 50% percent after the installation of the biodigester systems.

The human waste system is (and should remain) an ultimately hands-off process. A six-foot deep brick tank surrounded by an air seal was installed seven years ago and inoculated with bacteria to jump start the production of biogas. As the two toilets are flushed, they drain into the tank where the material broken down by the bacteria and transformed into methane which is piped directly to our stove top. The system involving cow manure demands daily attention, but can usually be tended within thirty minutes or less. It requires adding fresh cow patties (one and a half recycled rice bags for us) to a 55-gallon barrel and filling it up with water. It is necessary to pulverize the material so that it becomes water soluble – roughly 15 liters for every kilogram of organic matter. Here it is left to sit for a twenty four hour period prior to being pumped into the four barrels below. As the solids settle to the top, the liquid is moved through the series of tanks below before finally arriving in a PVC bag. The gas is captured and then join the same pipe before reaching the kitchen. The solids are tossed into a 14-day compost rotation before they arrive to the gardens to be sifted and applied to our beds.

Any technology that enables us to transform abandoned “waste” into usable energy shows much promise for small-scale homesteads striving for self-sufficiency as well as society at large. And that's not just another hippie talking s&%t.