Learn about biodigesters and how they can help you process chicken poop, from permaculture writer Jonathon Engels.
Where there are chickens, or any animal for that matter, poop is sure to follow. While this is often erroneously referred to as waste, the fact is that we can do lots of very useful things with manure. Most of us know of using it for fertilizing crops, and it’s no big epiphany that it can be added to compost. These are perhaps the most commonly practiced uses for manure.
There are other uses as well. In fact, not too long ago, Community Chickens published an article about using chicken manure compost to make hot water. Now, it’s time to look at how chicken manure can be used to make biogas, which can then heat a home or run a generator or even cook a meal. That’s right: Chicken poop can provide the gas to make chicken soup.
Survey Says: Biodigester
The key to converting poop into biogas is a biodigester. Biodigesters are airtight structures that are fed organic matter, including animal manure, so that it decomposes anaerobically within them. As the breakdown occurs, gases are naturally released inside the biodigester, transferred to an air bladder, and stored for later utilization. The bladder can be hooked up to a cookstove, heater, or generator to supply clean burning fuel: biogas. Biogas is chiefly composed of methane, with a notable amount of carbon dioxide and trace amounts of other gases, like hydrogen, oxygen, and nitrogen.
How Biodigesters Work: Belch-y Anaerobic Magic
Unlike the decomposition in healthy compost piles (aerobic), which is heavily reliant on lots of oxygen, biodigesters rely on anaerobic, or oxygen-deprived, decomposition. Anaerobic microorganisms (Archaea) are a very old form of life that occurred before plants were releasing oxygen into the atmosphere on earth. They are still around and hungry, but they need airless homes to survive.
Underwater inside the biodigester, naturally-occurring archaea happily break down organic matter, such as chicken poop, other manures (including human), as well as kitchen scraps. As this process occurs, the slushy substance inside the biodigester belches out biogas. This same action happens in swamps, known as swamp gas, and other places with water-logged soils, such as rice paddies. It also happens in digestive tracts.
Large-Scale Biodigesters: The Secrets of Sewage
Biodigesters are not anything new. They’ve been used in wastewater treatment plants for over a century now. In these systems, sewage enters a treatment plant and goes through a two-digester system. The first biodigester is used to breakdown volatile organic material, and the second one is used to separate remaining biosolids from the water. The gas produced from this is used to heat the digesters to specific temperatures in order to create ideal environments—mesophilic (86-100 degrees Fahrenheit) and thermophilic (122-140 degrees F)—for different types of anaerobic microbes to thrive. In the end, the once-harmful sludge is rendered safe and used on agricultural lands as fertilizer.
Energy Production from Industrial Farms: Chicken Houses Powered by Chicken Poop
With this process in mind, it only makes sense that places with a lot of errant feces—industrialized farms and feedlots—could take advantage. While pigs and cattle have led the charge on industrial manure biodigesters, big chicken farms are getting into the game now, too. Not only has it provided a more ecological means of dealing with the poop, but also it ultimately provides a savings because the birds are heating their own houses. In fact, the energy production provides a surplus that can run the homestead, as well as slurry that can fertilize the cultivation of chicken feed.
Backyard Chickens and Biodigesters
The confession here is that chicken poop is not the ideal choice for biodigesters. It’s on the acidic side, or a bit high in nitrogen. Cow and horse manure, on the other hand, are just about the perfect ratio of carbon to nitrogen (25:1). That said, chicken manure (6:1) with bedding will skew this ratio closer to correct. Food scraps, fresh grass clippings, weeds, and green leaves are also good ratios for biodigesters (and making compost). The point, however, is that when balanced correctly a small amount of chicken manure, as well as kitchen and yard waste, will work to produce biogas.
Making Your Own Biodigester at Home
Smaller biodigesters can be made at home with simple hardware available at any DIY store, as well as repurposed materials, such as shipping barrels and IBCs (international bulk containers). In fact, a couple of families with small farms could team up to efficiently provide plenty of gas for two households, maintaining multiple digesters but sharing a single, large gas storage container.
For those who are interested in experimenting with the idea, it’s also possible, and inexpensive, to build individual digester systems appropriate for a small, backyard flock and single-family amount of compost. These individual digesters would realistically provide enough gas to cook every day.
The Solar C3ities Mini-Biodigester Design Experiment
A mini-biodigester, aka “Baby Dragon”, can be constructed with a five-gallon water bottle and some basic plumbing fittings. While this won’t provide enough gas to do much cooking, let alone fuel a heating system, it does provide the nuts-and-bolts of how biodigesters work. The same principles apply no matter the scale, so this is a good experiment for curious adults and kids’ science classes alike. It might also be a good way to explain to friends and neighbors what exactly you are doing.
The Small-Scale Home Biodigester
Repurposed IBCs are great for home-scale systems. The container will have three pipes: a feed pipe for adding food scrapes and/or manure, a gas outlet pipe for harvesting the biogas, and an effluent discharge pipe for catching the liquid fertilizer that it produces after each feeding. The ideal content composition within the biodigester is 40% organic materials, 50% water, and 10% headspace for gas.
For a biodigester to provide reliable service, the gas-producing microorganisms require consistent feeding. Adding one and a half gallons of food waste, or five gallons of manure a day, realistically provides enough fuel for about two hours of full blast cooking time on a single burner.
Many home biogas producers elect to tie two or three digesters to one large gas bladder so that, if one digester needs to be adjusted, the other(s) can still provide gas. And, of course, gas production goes up without having to construct completely separate systems.
Storing Biogas for On-Demand Use
While most of us are accustomed to gas coming in pressurized bottles, this doesn’t work with biogas. Pressurizing it is too costly and involved for simple home systems, not to mention un-scrubbed biogas is corrosive to metal cannisters. Industrial systems clean the gas into pure biomethane to pressurize it in bottles. Home systems often use sturdy PVC bags.
At optimal conditions (about 95 degrees F), a biodigester will produce its own volume in gas each day, but obviously conditions are rarely perfect. Twenty-five gallons of biogas equates to about 15 minutes of cooking time. An IBC tote is usually around 300 gallons, which translates to a maximum of three hours of cooking each day, all things copacetic.
Using Your Own Gas to Cook
While biogas is clean burning and easy to produce, it does require specialized or adapted equipment to use it. There are specific cookstoves made to use biogas, which requires a larger opening than high pressure gases but doesn’t need the aeration that those gases use. These cookstoves are available online for less than $50.
Otherwise, typical gas appliances can be converted to work with biogas, providing virtually free energy for years to come. Propane, butane, and natural gas stoves can be easily altered to run on biogas by removing the pressure restrictor pin and covering the air intake on the gas-feed. This allows for converting things like barbecue pits, propane generators, and gas heaters to run off of biogas.
Full Biogas Systems Available for Purchase
For those who aren’t exactly DIY types but would be interested in using biogas, full home-scale systems are available for purchase, simplifying the process and providing peace of mind. HomeBiogas and Puxin are two companies that sell ready-to-roll systems, including biogas appliances to use with them.
HomeBiogas 2.0 System
Or, for more in-depth investigation about biogas production and self-made systems for non-professionals, The Complete Biogas Handbook is a sensible next step, with The Biogas Handbook being more focused on large biogas plants and the serious science involved on the industrial level.
Jonathon Engels is a traveler, writer, and vegan gardener. Born and raised in Louisiana, he’s lived as an expat for over a decade, worked in nearly a dozen countries, and visited dozens of others in between. His interests include permaculture, cooking, and music. More of his work can be found at Jonathon Engels: A Life About.