Biogas - The Basic Idea: "Anaerobic digestion. In the absence of free oxygen, certain micro-organisms can obtain their own energy supply by reacting with carbon compounds of medium reduction level to produce both Carbon Dioxcide - CO2 and fully reduced carbon as Methane - CH4. The process (the oldest biological ‘decay’ mechanism) may also be called ‘fermentation’, but is usually called ‘digestion’ because of the similar process that occurs in the digestive tracts of ruminant animals. The evolved mix of CO2 & CH4 and trace gases is called biogas as a general term, but may be named sewage gas or landfill-gas as appropriate." - Renewable Energy Resources, 2nd ed.

In simple terms... by taking manure and various vegetable matter and placing them in an oxygen free environment, the bacteria in the manure create methane gas which can be harnessed to provide fuel for cooking, heating, lighting, and even producing electricity via a generator. The output from the digester can be used as fertilizer, and it is even better than the manure itself.

Ugandan Context: In Uganda, approximately 90% of all cooking is done using the energy provided by buring wood and charcoal from cut down trees. With a population of 30 million people in an area the size of the state of Oregon, this practice is quickly resulting in deforestation. The wood that is used for cooking also presents a health risk for the people (primarily women) that use them because the cooking is often done in poorly ventilated rooms. The gathering of wood is also a major time consumer for the women and children that have to collect it on a daily basis.

Lango - Boroboro: We decided to build a biogas demonstration unit at the Bishop's house in Boroboro. His household is quite large, and they use wood and charcoal as their primary methods of cooking fuel. The Bishop also has many livestock from which manure can be gathered for the digester. He is also high-profile, so if the biogas unit proves successful, then people will be more likely to adopt the concept for themselves.

With this design we are hoping that a daily addition of .5Kg of manure mixed at a 1:2 ratio of manure to water will provide 5 hours of methane per day; enough to cook for the whole family without using wood.

Step 1: Dig a 2m X 2m square pit that is 2.5m (8.2ft) deep. We each took turns with hoes, pick axes, and shovels. I ran out of steam fast, and blisters began to form, so I just shoveled dirt. Even the Bishop got involved with the digging, and even though he is in his 50s, he is able to dig like a champion.

The fact that the Bishop came out to dig with us really helped to bring a lot of the other boys out to help as well. They really worked hard.

(In Photo: From Left: Paul, Bishop, Abel)

Step 2: The first half of the pit was relatively easy, but then we hit rock. It became such a slow process that we had to hire a digger to come out with a better pickaxe. He took almost two days to go 1m (3ft) .

(In Photo: Dale)

Step 3 & 4: The next step was to lay a foundation. The floor of the pit was basically filled with a few inches of cement and left to dry for 3days. After the 3 days they came back and built the first 1m of the main digester.

We had to build in 1m increments so that the masons could still reach down inside and plaster the insides in order to make it air and water tight.

(In Photo: Rolex mixing the cement, and Geoffrey and his asst building the first meter of the digestor)

Step 5: This portion was probably the most complicated part of the building. The 2nd meter of the digestor was built, bringin it to about ground level. The input and output sections were also built. We had to make sure that the output pipes were lower than the input pipes to insure that when the digester is full it will drain properly.

Thanks to Paul Vliem from CRWRC for supervising this for me that day, as I was sick in bed with malaria. He did a great job of orchestrating the most complicted part of the project. Paul helped a lot with the design of the whole project.

(In Photo: Rolex shoveling sand, and Geoffrey and his asst building the input tank)

Step 5 (cont.): In picture 1 (left) you get a view of the output tank where you would place a bucket to catch the fertilizer. In picture 2 (right) you can see the internal plastering on the inside of the main digester.

(In Photo: Geoffrey and his asst building the input tank, and Rolex standing behind the main digester)

Step 6: Now that the guys were almost done with the building, I had to go and take our metal barrel into town and have some metal rods welded into the inside.

The reason for these is that during the decomposition process that happens at the surface of the water, a crust can begin to form that prevents the gas from reaching the top of the barrel.

The idea here is to turn the valve off on the barrell, unhook the pipes, and then spin the barrel around and around. This should break up any of the build-up that occurs.

On the top of the barrel, two nuts were welded to the top of the tank so that a small 1/2" diameter pipe could be screwed into the top. A valve was then added to the end of the pipe. A handle was also welded onto the top in order to make it easier to fish the barrel out of the digester when it falls below the edge.

Step 7: The finished product. The builders plastered the outsides of everything that was sticking above ground just to make it look nice, and to protect the bricks from the elements.

As of June 19th, 2009 we are just beginning to fill the digester with manure and water. While it begins to produce methane over the next two weeks, we will be installing the pipes that run to the kitchen, as well as building the burners themselves. So check the site in a month or so for updates.

So far the whole project has cost less than 400,000 UGX ($200). By the time we are done, the whole thing will be no more than $250.

(Photo: from left: Input tank, Main Digester, Output tank)

Step 7: Left Photo - close up of the Input Tank. We will probably have to raise the height of this, but we will see what people prefer as they begin to use it. It also would have been better to have some sort of gate built into the input tank while the cement was wet. A miscommunication with the builder caused us to miss that opportunity. We will use a simple tapered stick carved to fit the input pipe to block the hole instead.

Right Photo - The Output Tank basically is set up so that you always keep a bucket under the tap and then go and dump in in the garden when it is full. There is a drainhole in the bottom to keep overflow and spillage from stagnating in the bottom.

Lids might be added to both of these if it becomes necessary.

(Photo 1: Input Tank -- Photo 2: foreground - Output Tank)

Test Phase: After about a week the drum began to rise. The input and output levels were right on, allowing the drum to rise only so far without tipping over the edge.

Week 1: Drum rises, but the gas is not flammable. So, we just emptied it completely, letting it sink to its lowest point. We were careful to shut the valve off just before it was completely empty, in order to keep the outside air from getting into the drum. Oxygen is the enemy here. Letting it sink to its lowest point and then closing the valve also creates a suction inside the barrell, making the drum vitually heavier. Hopefully this with compress the gas a bit, allowing for more storage.

Week 2: After a week we tested it again, and IT WORKED!!! (see photo: bottom-right). The methane is finally the dominate gas in the system.

The long horizontal pipe that you see coming out of the drum (see photo: top) is just for testing the gas. It will actually be used as a homemade burner in the kitchen when we finally run the pipes to the kitchen. Basically we just used a hacksaw to cut some small slats in the pipe (See photo: bottom-left). It works surprisingly well. Before we place it in the kitchen, we will make even more of them to distribute the flame evenly over the bottom of the pan.

Week 3: The gas is replenishing itself within a day and a half now. When it gets full you can actually see a slow stream of bubbles coming up the side of the drum.

Testing Phase - Week 4: We finally got the pipes to run gas to the kitchen (about 26m away). I still need to get some pictures posted for this. We have made one test burner and it is working well.

Big problem-- For some reason the drum is not heavy enough to create pressure on the line. Solution: put bricks on the drum. It is now working well. If I were to build it again, I would probably poor some cement in the top of the barrel to make it heavier and cleaner looking. For now, bricks will do.

Bigger Problem-- A full drum of gas is only holding enough fuel for about 40mins of cooking. Barely enough to boil a pan of water. This is a huge problem. 2 possible solutions: (1) get another drum and weld the two together. This would be a huge, messy pain. But, it might solve the weight problem and the storage problem. We might have to raise the level of the bricks to keep it from tipping. (2) The other solution might be to cut into our gas line running to the kitchen, and put a T-fitting there, running another pipe to a safe, shady place where we could attach a small hose to a large, truck inner-tube. This could act as storage, and might also help with pressure problem. It would also allow for easy expandability, if one is not enough. This one sounds best. I will start to put this together and post the results soon.