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How to produce usable methane gas: turn manure into fuel.


One day, while cleaning out from under my chicken cages, I thought to myself, "There must be a better use for this manure than composting." Don't get me wrong, compost is great to have, but you can only use so much of it. I remembered reading an article several years back about converting animal waste into methane gas. With nothing to lose, I set out to learn as much as possible about the digestion process.

During the learning process I made two very important discoveries. First, I discovered how hard it was to find any books on the subject, and second, what information I could find seemed to make the whole process sound very complicated. Not worrying about how complicated it sounded I kept telling myself, "This is a process that occurs all by itself in nature, so how hard can it be?"

It seems that in the early '70s, while the first so-called energy crisis was going strong, much was written about methane digesters (or bio-gas plants as they are sometimes called). In the mid '70s The Mother Earth News ran several articles covering the subject of methane production. One article was an interview with Ram Bux Singh (Mr. Singh was responsible for much of the research on small scale digesters) of the Gobar Gas Research Station in India. The Indian government saw the digester as a means of manure disposal and a source of very high quality fertilizer while providing methane gas as a cooking and lighting source. During the '60s India had more than 2,500 methane gas plants of various sizes. Mr. Singh wrote a book called Bio-gas Plant which detailed much of their work at the Research Station. I'm not sure if this book is still available, but it would be worth looking for. The Mother Earth News also produced a book called, The Mother Earth News Handbook of Homemade Power (published by Bantam Books), that contained valuable information on methane and several other types of homemade power. This book is no longer in print, but you should be able to find it at a large library.

One other book that might be of interest, is Producing Your Own Power (published by Rodale Press). These books will probably be hard to find, but I recommend that you at least find The Mother Earth News Handbook of Homemade Power. It will give you more than enough information to build a working digester.

Methane is produced by the action of anaerobic bacteria (without oxygen). Aerobic bacteria (with oxygen) are the little guys that break down raw materials into compost. The difference between a compost pile and a digester is the presence or lack of oxygen during the break-down of the organic matter.

The object then, is to provide an oxygen-free environment where our waste can be converted into methane. This is where the digester enters the picture.

There are two types of digesters, batch and continuous feed. A batch digester is filled with material, sealed off, and left to produce gas. The continuous feed unit has openings that allow you to feed fresh waste to the unit and remove spent slurry. The batch digester is the easiest of the two units to construct, and less maintenance is required while it's producing. I will admit that it is a little incovenient to load and unload the batch unit, but it only needs to be done every three to six months.

My experiments have been with small scale batch units capable of producing small amounts of gas on a daily basis. To learn about the process I built a very small unit that would produce about eight minutes of gas a day over a 60 to 90 day life. This digester is built using a one gallon pickle jar and should be simple enough for anyone to build, and it will also help you learn how the whole thing works.

Start with a clean one gallon glass jar with a good lid. Drill a hole in the lid and fasten a pipe fitting to the top. I used a 3/8[inches] plastic tee made for sprayer units which can be found at most tractor supply stores. This tee has an 11/16[inches] threaded end and can be installed using two rubber washers that fit in the end of a water hose. To install it, place a rubber washer on the tee and insert it in the hole in the jar lid. Next, add a small bit of silicone sealer around the threads where they enter the hole on the under side of the lid. Now place the other rubber washer on the tee and install the plastic nut and tighten firmly.

For the next part you will need to gather a few supplies. First is a small bicycle tube, the type that fits a 16[inches] to 18[inches] bicycle should be about right. (Stick to the larger size tubes; they seem to be less trouble). You'll also need some 3/8[inches] and 5/16[inches] gas line, several small hose clamps, a 3/8[inches] to 5/16[inches] hose reducer (a little thing that accepts several different size hoses and has little ridges that hold the hose on), and some type of cutoff valve. I have used many different types of gas cutoff valves, aquarium air valves, old gas heater valves and utility valves. Be creative, but keep in mind that methane is one of the lightest gases known to man, so use a good valve.

To hook up all this stuff we will start by cutting a 4[inches] or 5[inches] length of 3/8[inches] hose and attach it to one side of the 3/8[inches] tee with a small clamp. Insert the hose reducer in the other end of the 3/8[inches] hose and a 16[inches] to 24[inches] piece of 5/16[inches] hose on the other end of the reducer. Use small clamps to secure the hoses to the reducer. Next remove the valve core from the inner tube and push the 5/16[inches] hose as far as you can over the valve stem and clamp it down. You should now have a hose that runs from the tee to the tube.

The next step will depend on what type of cut-off valve you have chosen to use. I will explain how I do it and you can adapt your valve with a little ingenuity.

I use a cut-off valve that has 1/4[inches] pipe threads on each end. Use some Teflon pipe tape and install a 3/8[inches] hose between the tee and the gas valve.

The last step is to find or make some sort of burner. You can make a burner by taking a 1/4[inches] piece of glass lab tubing and holding it over a flame. Keep twisting it until it thins out in the middle. After it has colled break it at the thinnest part. You should have a pointed piece of glass tube with a small hole in the end.

You can also use copper tubing by capping one end and drilling a small hole in the middle of the cap. I like to lightly stuff the tubing with steel wool to prevent the flame from flashing back down the tube. Attach the burner with a length of 1/4[inches] hose and your digester is ready to fill.

To fill the digester you can use almost any type of organic matter, but I would suggest you use animal manure. Any manure will work, although I use chicken because that's what I have available. You will need to mix the manure with water until it reaches a cream-like consistency. Warm water is best and will help speed up the process, although it is sometimes inconvenient when working with large digesters.

Pour the mixture in the digester, filling it no more than 3/4 full. Now place the top on tightly, open the valve, squeeze all the air out of the tube and close the valve. Place the digester in a warm place (above 70 degrees; I put my small unit on top of the water heater in the house). The temperature can be anywhere from 65 to 105 degrees with the best being 85 to 95 degrees. Big digesters located outside can be heated or have a small plastic greenhouse placed over them. A simple frame with 4 or 6 mil plastic is more than enough for most locations. The temperature of large units doesn't fluctuate as much due to their larger volume. My 55 gallon unit had nothing but a sheet of plastic draped over it during cold weather and worked fine.

For the next few days the digester will produce a lot of carbon dioxide that will need to be emptied once a day for about a week. The anaerobic bacteria will not start working until all the oxygen is used up. The anaerobic bacteria grow very slowly and will take several weeks to make any usable gas.

You may notice after about two weeks a small amount of gas has been produced along with carbon dioxide. Bleed it off and continue to wait.

After about 4-5 weeks you should be making a tube of gas about every three days. This gas is not of good quality because it still contains a lot of carbon dioxide; burn it off every time the tube gets full and the quality will start to improve.

At about 7-9 weeks your digester should be producing large quantities of very good gas. You may need to burn it off 2-3 times a day. I have burned off the gas in my small digester to impress my friends. I have also run my small yard tractor on the gas by removing the air cleaner and placing a hose down the carburetor. I then started it on gasoline, and after it was running clamped off the gas line. When it started to run out of gas I slowly opened the valve on the digester and adjusted it until it ran smooth. It continued to run for about five minutes at medium throttle.

After about three months gas production will drop off fast. When the digester is through producing you can use the remaining slurry as an ammonia/nitrogen fertilizer of the highest quality and start the whole thing over again.

I have also built large digesters out of 55 gallon drums and tractor inner tubes. Use a 6[inches] 3/4 pipe nipple, a 3/4[inches] tee and a couple of cut off valves. Screw the 3/4[inches] pipe in the small bung hole and fill it from the large hole.

I have included a photo of my first large digester made from a plastic drum. I do not recommend using a plastic drum because of the problems I've had sealing it off. After it started producing gas it developed a leak where the metal pipe screwed into the plastic bung hole. I was never able to stop the leak and lost all but a small amount of gas.

I don't have any production records at the time it reached full digestion but can tell you it will make 25 to 45 minutes of gas a day. You can connect several units together for longer burn times. For continuous production, start each digester at different times.

You need to keep a few things in mind as you work with your digester.

(1) Methane is very flammable and must be treated with great respect and lots of ventilation.

(2) Methane can be used anywhere natural gas is used.

(3) Don't expect gas overnight. It takes several weeks for a digester to produce methane. Most books I've read make it sound like it will make gas in 2-3 days. While it's true that gas will be produced in a couple of days, it won't be methane. The biological process makes large volumes of carbon dioxide as it breaks down the manure into its simpler components. Carbon dioxide is useless as a fuel and needs to be released from the digester to speed up the breakdown.

(4) Temperature makes a big difference when the anaerobic bacteria start to work. Try to keep the digester above 70 degrees and below 105 degrees.

(5) There are many different ways to store the gas besides the inner tubes, but remember, you must keep all air out of the gas or it becomes extremely flammable.

My experiments with digesters have been conducted to prove that the concept works. I am now working to find ways to put all this gas to work. My main project is building a methane powered generator to keep my emergency batteries charged. I hope to be able to run gasoline and methane in this generator just in case gasoline gets hard to find.

We had a huge ice storm here this year and were without power, phones and water for several days and some people went without for several weeks. We were able to make it fine through the great ice storm because we were prepared. I had battery power to run my lights and tv, a gas grill with several spare bottles of gas to cook with, and thanks to an article in COUNTRYSIDE we had water stored for just such an occasion. I would like to hear from other people about the way you use alternate forms of energy to power your homestead.

In closing let me reassure you that if you place any type of manure in an airtight container it will produce methane gas. The quality or quantity may not be very good but it will make gas.
COPYRIGHT 1994 Countryside Publications Ltd.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1994 Gale, Cengage Learning. All rights reserved.

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Author:Turner, Tony
Publication:Countryside & Small Stock Journal
Date:Sep 1, 1994
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