Biogas Systems

Biogas typically refers to a gas produced by the breakdown of organic matter in the absence of oxygen. It is a renewable energy source, like solar and wind energy. Furthermore, biogas can be produced from regionally available raw materials such as recycled waste and is environmentally friendly.

Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops.^[1] It is primarily methane (CH
4) and carbon dioxide (CO₂) and may have small amounts of hydrogen sulphide (H
2S), moisture and siloxanes.

The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.^[2]

Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel.^[3] It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards when it becomes bio methane.

Construction Instructions

(Before begining construction, view the "Start-up Instructions" below for some prep operations.)

1. Select a location for the HBS close to where the gas will be used. (We recommend collecting manure and bringing it to the HBS for feeding.)
2. Choose a location away from trees whose roots can break the digester walls. (Min area: 2.5 mtr x 3.0 mtr)
3. Dig the ground 2.5m x 2.5m wide and 2.0m deep.
4. Build the footings and reinforced concrete slab.
5. Build the reinforced CHB walls. Upon reaching ground level, layout CHB walls for outlet compartment so that CHB and rebar interlocks are maintained. (Do not install all CHB for outlet compartment. See instructions below regarding cover installation.)
6. The HBS has a below ground section of about 1.6 mtr and an above-ground section of 1.0 mtr. (This UNIQUE feature expedites sediment removal as described later in operation & maintenance.)
7. After the CHB walls have dried, install the inlet, outlet and other pipes. Pipe locations may be changed to same or adjacent sides if preferred or needed.
8. Install anchor bolts on the outside wall.
9. Build the concrete slab for the outlet compartment and plaster the inside and outside walls. Use plaster mixture with a water sealer like Sahara.
10. Cut the 6” orange PVC pipes in half and lay them on the CHB blocks. Place elbows (also cut in half) on the corners. Grout as needed to keep them in-place. (This is to protect cover material from sharp edges.)
11. Clean the surfaces of the halved 6” orange PVC pipes and ay the HBS cover as if installing a table cloth.
12. At the outside CHB wall section, where the anchor bolts are located, apply a 6” to 8” wide strip of sealant like Vulca-Seal. Ensure good sealant & plaster adhesion.
13. Remember, after the cover material is sandwiched between the outside plaster and the wood plank, the sealant must create a gas-tight seal.
14. On the wall adjacent to the outlet compartment, it is best that some CHB was omitted earlier to allow for HBS cover installation. Install the omitted CHB after the cover.

Benefits

When biogas is used, many advantages arise. In North America, use of biogas would generate enough electricity to meet up to 3% of the continent's electricity expenditure. In addition, biogas could potentially help reduce global climate change. Normally, manure that is left to decompose releases two main gases that cause global climate change: nitrogen dioxide and methane. Nitrogen dioxide (NO
2) warms the atmosphere 310 times more than carbon dioxide and methane 21 times more than carbon dioxide.

By converting cow manure into methane biogas via anaerobic digestion, the millions of cattle in the United States would be able to produce 100 billion kilowatt hours of electricity, enough to power millions of homes across the United States. In fact, one cow can produce enough manure in one day to generate 3 kilowatt hours of electricity; only 2.4 kilowatt hours of electricity are needed to power a single 100-watt light bulb for one day.^[15] Furthermore, by converting cattle manure into methane biogas instead of letting it decompose, global warming gases could be reduced by 99 million metric tons or 4%.

In Nepal biogas is being used as a reliable source of rural energy, says Bikash Haddi of Biogas promotion center.