methane

The production of methane on both a large or small scale is achieved using one or the other of the following methods. 1 Batch digestion. 2 Continuos digestion.

A digester is that which in fact replicates the processes going on in the digestive tract of all warm blooded creatures even humans. The requirements are a lack of air, warmth 85_100 f agitation and a source of raw material. There is also a requirement to maintain an accurate PH level. PH is the measure of acidity or alkalinity of the mixture

For those of you that are contemplating the construction and use of one of the above devices I will WARN YOU NOW that the source of your organic feed stock (Manure) needs to be just that, Raw feed from any form of battery farm or intensive farm is to be avoided at all costs. Unless they have been certified as an organic grower. Most intensive farms use anti-biotics to stop the spread of disease amongst the stock and these pass the digestive tract and appear in the manure. THEY WILL KILL YOUR DIGESTER VERY QUICKLY.

1 Batch digester..

A batch digester is just as it sounds, a container usually with a built in gasometer is filled with a given amount of organic material and then sealed, the mixture is allowed to start fermenting and will proceed through the stages of fermentation producing methane gas until the potential to maintain production fails due to a lack of organic fuel. At this point in time the tank will have to be opened and the contents replaced with a fresh batch. If you are contemplating this method then it is advised that you have at least three digesters working at the same time but they should be started three or so weeks apart. Doing this will maintain a constant production of methane..

2 The Continuous Digester..

By far the more popular of types is the continuos digester this device allows for the feeding on a daily basis the raw feed stock as it becomes available. Via a series of gas tight inlet and outlets material is added and at the same time used or digested material is removed from the tank.

The digested material is about the best organic fertiliser that you can find as the bacteria have converted what was a smelly mess into readily available plant nutrients with no odour. The down side to this method is that a system infection or death means a restart and a lack of gas for a period of time. Two systems side by side would provide some redundancy.

Some considerations.

For correct fermentation to occur in any of the above digesters the attention should be paid to the following areas.

Temperature:
The bacteria that produce methane are sensitive to large or rapid swings in the mix temperature. If it is to cold they will slow production rapidly and then become dormant. To hot on the other hand will cause death and will require the system to be re seeded with fresh bacteria when the mix gets to the normal temp. The ideal temp is some where between 85f and 105f In fact on several systems I installed we thermostatically controlled the temp at the average body temp of the type of animal producing the feed stock (this worked extremely well).

Using a methane generator in cold climates will require that the tank be insulated against heat loss and that some form of indirect heating is employed. The required heat can be produced by burning some of the produced methane. Not a lot of gas is required for this, in fact in a properly balanced and insulated tank the bugs will generate some of there own heat.

Please note that wet or damp insulation is no insulation.

In a warm climate it will be important to shade the tank from most of the direct sun if it is mounted above the ground. In a worst case situation then even some cooling may be required.

It is important to note that when adding material to the tank with a continuos digester that the new material be at or very close to the operating temp of the system, otherwise thermal shock will result and a decline in gas production will result.

Ph and Carbon balance:

Now this can be easy or a real can of worms it depends on what you want to make it, so I will tell you what I do. On all the tanks I have built I install a tap off or draw down point in the side of the tank about 12 inches or 300mm down from the average liquid level. From this point I can take a small amount of fluid to use for testing the Ph level. To do this test I use a simple electronic Ph meter sold at swimming pool shops. You can also buy cheap test strips that you dip in the sample these work best in clear water your sample will more than likely be black and unless clarified may give a false reading (you can settle the sample buy placing a small quantity in the fridge). Once it has settled out allow it come to room temp and then test with the strips. The reason Ph is important is that most bacteria do not like an acid environment certainly not the type that makes the methane. This may sound like a contradiction but the bacteria in a new batch of material will actually produce an acid and this starts the initial break down of the feed stock (we have strong acid in our tummies for the same reason).

The acidity must not be allowed to get out of proportion or problems will develop, So to buffer or balance the mix we add a small amount of Bicarbonate of Soda (baking powder). This will ensure a happy bug population that will slave away eating poo and making nice methane for you to use for whatever you have in mind. Any adjustment in Ph must be done slowly so as not to create rapid swings in the acid or alkaline levels these are detrimental to the health of your bugs.

Carbon:

There is a need to balance the amount of Nitrogen with some Carbon to keep the system in Equilibrium, Carbon can come in many forms, Straw, Paper etc but it is best to use that which is readily dissolved and available to be digested. The amount of carbon input will be dictated by the type of feed stock, Often the material from a stable or cow barn will have enough carbon but the output from a pig pen or human waste source will not.

Are you confused yet, I hope not. What I am trying to do is give you enough information so that you do not fall into the same holes that I did.

I have a lot of friends in the RE hobby, They have magnificent machines They work when the wind is blowing, others have spent a lot of money on solar cells and devices to track the sun. If you are lucky about 7 hours a day. Here we are talking about happy little bugs that will produce methane 24/7/365 Methane is power!

A little more on carbon before we move along, Straw is a good source of carbon but common hay is not. Timber or grass clippings are to be avoided at all cost. Most soft or old vegetables should be mashed and soaked before being added to the digester. In fact anything containing large quantities of lignin is to be avoided. Grass clippings have to much lignin.

Lignin is to slow to break down to a soft enough compound for the bugs to eat.

But the digester is a great way to dispose of all your old paper etc, junk mail and stuff soak it for a few days in a bucket of water out in the sun mash it up a bit and then add to the system. Make sure it is warm before adding it.

A little about the ratio of carbon to nitrogen:

The ideal ratio is 30 parts carbon to one part nitrogen = happy bugs. This is an ideal ratio but variations even wide ones will still work. A compromise will only reward you with a smaller amount of gas per pound of input material.

Sorry guys and galls but I have to digress a little here,

Methane its self is a gas that is extracted from under the ground and is a product of the long term fermentation of vegetable matter many thousands of years old and usually found in conjunction with coal seems or petrochemical deposits. Sometimes called natural gas.

Bio-gas refers in general to a gas produced in the short term (maybe several weeks) by the digestion of Bio-mass.

Gobar gas is the same as bio gas, But I like the term. Gobar is an Indian description of cow shit, and god knows they have plenty of that. In the south east Asian countries almost all the digesters are referred to as Gobar gas generators.