Methane, also called biogas, can be used for a variety of applications from cooking to fuel for combustion engines. Methane burns very cleanly, and making it is a carbon-neutral activity, as it is simply speeding up and trapping a process that would have taken place naturally. Chicken manure is a good choice for making methane. A single pound of poultry droppings can produce up to 0.3 cubic metres (10 cubic feet) of gas, more than any other livestock waste. After the gas production is complete, the leftover sludge is excellent garden fertiliser.
- Skill level:
Things you need
- Power drill
- 208 litre (55 gallon) drum, plastic or metal
- 113 litre (30 gallon) drum
- 1 cm x 5 cm (3/8 inch x 2 inch) brass nipple
- 1 cm (3/8 inch) rubber gasket
- 1 cm (3/8 inch) brass compression nut
- 1 cm (3/8 inch) gas ball valve, female both ends
- 3 m (10 foot) natural gas hose, 1 cm (3/8 inch) male one end
- Long stick or paddle
- Chicken manure
- Straw, newspaper or spilt feed
- pH meter
Drill a 1 cm (3/8 inch) hole through the bottom of the 113 litre (30 gallon) drum, 7.5 cm (3 inches) from the outer edge. To the threaded nipple, screw on one bolt, insert the nipple into the underside of the hole. Screw the gasket and valve onto the other end of the threaded pipe and connect the hose to the valve. When closed, the assembly should form an airtight seal.
Fill the 208 litre (55 gallon) drum with a chicken manure/water slurry made of three parts chicken manure to one part water. Add a few handfuls of shredded newspaper, straw or old feed. Stir gently to remove air bubbles and thoroughly mix the contents.
With the valve open to release air, carefully lower the 113 litre (30 gallon) drum bottom-up into the slurry inside the larger drum. Important: the smaller drum should fit close to the sides of the larger container, but not so snugly as to restrict vertical movement. Once the smaller drum is to the level where slurry will start to come through the hose, close the valve. If needed, weigh down the smaller drum to keep it fully immersed in the slurry.
Tips and warnings
- The largest drum serves as the digester. As the gas byproducts of bacterial action collect in the smaller drum, gas will rise out of the slurry. Pressurise the gas by adding weight to the collector. At first, much of the gas that is produced will be carbon dioxide, but in a few weeks methane-producing bacteria will take over. To test the gas composition, attach a Bunsen burner or gas grill to the hose. When the gas burns, it's mostly methane. To see an example of a similar system, see the first item in Resources below.
- The basic mechanics of a methane production system are simple, but success is dependent on several factors:
- 1. Temperature is critical. Chicken body temperature is 39.4 degrees Celsius (103 degrees Fahrenheit), which is the ideal for methane production. While the anaerobic composting process does generate some heat, it won't fully do the job, and external cooling will slow down bacterial activity. Paint the digester black so it can absorb heat from the sun. In cold weather, methane production may slow down considerably.
- 2. The first part of the composting process creates acid, which inhibits anaerobic bacteria. Check the pH of the liquid and add baking soda as needed to bring the level to within the range of 6.8 to 7.4.
- 3. If the water has been treated with chlorine, allow it to sit in the sun for a day or two before adding the manure. The volatile chlorine will dissipate so it cannot harm the bacteria.
- 4. Ideal composting requires a ratio of around 30 parts carbon to one of nitrogen. Manure is about 15-to-1, so the addition of carbon-rich materials that soften in water, such as newspaper or straw, will speed up methane production.
- 5. Methane is a byproduct of composting without air, so seals must be airtight. Methane dissolves many epoxies and glues, so don't use them to create the seal and check often to make sure air isn't entering the system.
- 6. Frequent gentle stirring of the compost mixture exposes more surfaces for bacterial activity, speeding methane production.
- 7. Methane is lighter than air, and carbon dioxide is twice as heavy. If the gases settle in the collector, a second valve to bleed off the unwanted gas from the bottom of the container will yield purer methane. Bubbling the gas through water will also purify the methane somewhat, as the water will absorb much of the carbon dioxide.
- 8. The composting of the slurry should be complete in about 90 days. Add the sludge to the garden and refill the container for a new batch of methane.
- 9. More weight on the smaller container will increase gas pressure.
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