A guest post by Robert P
[This is an entry in our non-fiction writing contest where you could win - First Prize a 10 Person Deluxe Family Survival Kit, Second Prize an Herb Seed Bank or Third Prize a copy of Dirt Cheap Survival Retreat. For complete rules and list of prizes see this post.]
I have learned a lot from this website from food storage, gardening and a prepping in general. One of the main concerns for all of us who are prepping is the energy we will need to survive if things ever get out of hand.
I see most of the information posted dealing with either the storing of petroleum products we can’t replace or solar energy. Do not take this the wrong way these are great alternatives and should be looked into and done, solar energy can provide years of reliable electricity to help fuel our way of life but most on this website feel that natural gas is something we cannot make ourselves.
I would like to argue that point because it can be done from just a couple cubic feet per day to thousands of cubic feet per day if you have the resources and the time.
I will say that most of us are capable of producing 20 or 30 cubic feet per day. This is not enough to heat your home and the modifications necessary to do that is probably beyond what most of us can do or should do. But we can use the fuel to supplement the fuel we have stored away for cooking, and water purification.
The process I am talking about is anaerobic digestion of plant and animal waste (manure not animal pieces and parts) this is a well understood science that is used around the world and is one that the homesteader can use for a very small investment.
I know you see anaerobic and everyone shies away from it thinking that they are a bad thing, in your compost pile it is. In a controlled environment they are actually a very useful bug. Anaerobic digestion of decomposing plant and animal waste has three main byproducts carbon dioxide and methane plus a very good fertilizer when it is all said and done.
There are two main types of digesters plug or continues feed digesters and batch type digesters. The plug type you add material on a regular basis while removing the same amount. With the batch type digester you fill it to begin with and let it do its thing once its done you empty and start over.
The plug flow digester is a larger system designed for people with multiple cattle and such who have a steady supply of organic matter, they are also a little more complicated to run and design. The batch type digesters are very easy to build and maintain require attention only when emptying and filling the digesters so I will concentrate on the batch as it is the one I feel most of us can benefit from.
A few quick pointers about bio gas and bio gas digestion
1. You are making a gas that is 50% methane and 50% carbon dioxide. Methane gas in the right concentrations is highly explosive unless you want to be on the 6:00 o’clock news because your house blew up be extremely careful with this stuff. What you are making can and will kill you if you do not take the necessary precautions. don’t get me wrong this system can be very safe and affective but when you work with it double-check everything and never store any of this in a house or other enclosed area.
2. You can use any plant matter for the digester and animal manure, never use animal carcasses, flesh bone and blood. The anaerobic bacteria turn this into hydrogen sulfide a flammable gas with a very objectionable odor smells like rotten eggs, it may or not be dangerous as well but it is to be avoided . The anaerobic bacteria need a carbon to nitrogen ratio of roughly 30-1 so a great way to get rid of the falls leaves that are in the yard.
3. The anaerobic bacteria are found in nature when you seal the container but you can speed up the process by adding a couple shovels full off fresh cow manure or by using a seed from a digester you are cleaning out.
4. The process requires a temperature range of 59 to 122 degrees but they do best at the higher end close to 100 is normally good. They do not like major fluctuations in temperature so insulation will normally be required. I have some ideas about this to be included later.
The basic batch type plant is very simple to construct with common everyday items. For the digesters I would use plastic 55 gallon drums that the whole top comes off. To the lid of these you want to put a pipe connector this is where the gas will leave the digester and go to your storage tank.
To this you want to have the gas pass through a water trap to make sure that if the gas catches fire it cannot reach the digester. The gas is then piped into a gas storage tank which is simply a 55 gallon drum with no top on it filled with water then you have a smaller drum with no top on it put inside the 55 gallon drum upside down so when the gas leaves the pipe it is caught in the upside down drum.
You place stone bricks what have you on top of the smaller drum so that it can hold more gas by pressurizing the gas slightly. Another gas line is connected to the smaller drum in what would be the bottom but is now the top, this is piped through another water trap then on to your point of use, propane grill or Coleman burner would be my suggestion.
This gas is 50% methane and 50% carbon dioxide and it isn’t truly natural gas as it has about half the energy of natural gas at 500 BTU per cubic foot it is called power gas. You can technically use it to heat and cook in your home but ports and burners need to be changed out to do this and I am not sure how all of that works I would do some serious research before I tried it.
On average the digesters should produce roughly 7 cubic feet of gas per day as it generally produces the same amount as the size of the digester. So each digester of this size should produce 3500 BTU of gas per day, there are a lot of variables in this however. The temperature is the largest of these followed by the feedstock. With just a couple of these you should easily be able to boil water cook a meal and such.
To fill the digester you want to crush, shred the feedstock as much as possible as the bacteria feed off the edges of the material this will make it produce gas much faster but for a shorter period of time. Fill the drum with your feedstock as tightly as you can to about 3 inches below the top of the barrel fill with water and put the cap on. If you have access to fresh cattle manure a scoop of that would speed up the start-up time as the high volume of anaerobic bacteria in cattle manure.
When the digester is sealed the first couple of days up to a week the digester will provide mainly carbon dioxide until the oxygen is consumed inside the digester.
When the digester is finished it will no longer be producing gas there for no bubbles in the water trap. It is time to clean out the digester and start over. The easiest way is to use a five gallon bucket and dip out as much material as possible this can be used directly in the garden and is a very good fertilizer.
When you can’t dip out anymore of the material simply pour the rest into buckets as it will now be far lighter. You may want to save a small bucket or 2 litter bottle of the affluent sealed and kept out of the light as a seed for the next batch.
To keep the digester warm and a stable temperature I would suggest covering it in compost as the heat from the composting will heat the digester while keeping it insulated from temperature fluctuations due to changing temps during the night and week to week.
There is no limit to the number of digesters you can connect other than availability of feedstock.
At this scale this is not the answer to all of your energy needs but it should be able to fill at least a portion of your energy needs. Digesters started in late spring or early summer should be coming on-line real well to help in the canning season. Allowing you to save your wood and other stored fuels to keep you warm in the coming winter which is critical. This may not be a total energy system but it is another feather in your cap to help when it counts.
There are a lot of resources for this on the web I invite you to look into them. Ram bux singh is considered a pioneer in the field and ran a huge system in India, just google anaerobic digestion, and bio gas and you will find a wealth of information. I hope I have provided a basic understanding of the system and opened up a few eyes to another energy system. Good luck, god bless and happy prepping.