Household Biogas Systems

by Catherine Haug (Jan 17, 2011)

(photo of stirring a biogas digester from PACE Project (3))

Our Flathead County Landfill and Flathead Electric Coop are experimenting with a large-scale biogas unit at the landfill to produce power (see Terrapass.com (6) for more). But smaller, household-scale units can also be deployed.

As we here in the Flathead prepare for a time when electricity and gas are in short supply, we might consider household biogas units as a means of providing light, heat and electricity, as well as a means of reducing waste.

Small biogas plants in underdeveloped countries

World Wildlife Fund (WWF) has been involved with an innovative program in a region of Nepal and India, to “avoid degradation of the forest” and its impact on vital tiger, rhino and elephant habitat in the area.(1) Similar projects are underway in other Asian and African countries.

The project provides household biogas plants to capture methane from fermenting human and animal waste. This gas is then piped into the home to be used as fuel for cooking, instead of burning wood. These plants are relatively small, and are manually operated. You can see a 7 minute video about this project on You Tube (1):

Video: Biogas – A New Source of Energy for Nepal

Regular use of a single biogas plant can save 60 tons (120,000 pounds) of fuelwood over the 20-year lifespan of a unit. (1) And by reducing the amount of fuelwood that is burned, the project also reduces the amount of wood smoke pollution and particulates that are already causing health problems in the children. Another benefit is turning human and animal waste into a useful product.

The systems produce:

  • gas for cooking/heating/lighting, and
  • effluent which can be used for fertilization of crops, much as humanure is used.

What biogas can do

1 cubic meter of biogas can (3):

  • give as much light as a 60-100 Watt bulb for 6 hours
  • cook 3 meals for a family of 5 – 6
  • replace 0.7 kg of petrol
  • generate1.25 kilowatt hours of electricity

Small domestic biogas systems

You can find instructions for constructing a unit on the Angelfire website (4)

Components

A small domestic biogas system will typically consist of the following components (2):

  • “Manure collection: raw, liquid, slurry, semi-solid and solid manure can all be used for biogas production.
  • Anaerobic digester: The digester is the component of the manure management system that optimizes naturally occurring anaerobic bacteria to decompose and treat the manure while producing biogas.
  • Effluent storage: The products of the anaerobic digestion of manure in digesters are biogas and effluent. The effluent is a stabilized organic solution that has value as a fertilizer and other potential uses. Waste storage facilities are required to store treated effluent because the nutrients in the effluent cannot be applied to land and crops year round.
  • Gas handling: piping; gas pump or blower; gas meter; pressure regulator; and condensate drain(s).
  • Gas use: a cooker or boiler (EPA, 2010).”

From PACE Project (3):

“The waste is fed into the digester via the inlet pipe and undergoes digestion in the digestion chamber. The temperature of the process is quite important because methane-producing bacteria do their work best at temperatures between 30 – 40oC or 50 – 60oC. It takes from 2 to 8 weeks to digest a load of waste, depending on the temperature. The left-over slurry is removed at the outlet for use as a fertilizer.

[The size of a digester] will depend on how much biogas you need to meet your daily cooking (and lighting) requirements, the availability and amount of livestock manure and water (water, number of cows, goats or other livestock), and the materials available on site (bricks, etc) for construction of the digester.

A regular supply of water is essential for operation of biogas plants. Rainwater harvesting could help with this”

Cost of a unit

A fixed- or floating-drum digester costs $800 – $17oo (3).

References

  1. WWF Jan/Feb 2011 Newsletter; see also WWF Nepal Biogas Voluntary Emission Reduction Project and video: Biogas – A New Source of Energy for Nepal
  2. CimateTech Wiki: Biogas for cooking and electricity
  3. Pace Project: Biogas Action sheet 66
  4. Biogas for overseas volunteers, by E. G. Matthews
  5. Biogas Manual: Sustainable Energy Solutions to Reduce Poverty in South Asia
  6. www.terrapass.com/projects/details/flathead-county-landfill-gas-t.html

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