In Perspective - Biodigesters

In the past months I have focused on energy and the residential power supply. What I have neglected is the local farmer and their sources of power. Farms and ranches can use anaerobic digesters, or the biodigesters, to recover methane from animal waste for producing electricity, heat, and hot water. Anaerobic digesters not only reduce energy costs for farmers but also reduce methane emissions, which contribute to global warming.

Methane, the major component of the "natural" gas, is a gas that contains molecules of methane with one atom of carbon and four atoms of hydrogen (CH4 ). It is the gas used in many homes for cooking and heating. It is odorless, colorless, and yields about 1,000 British Thermal Units (Btu) of heat energy per cubic foot when burned.

 All anaerobic digestion system designs incorporate the same basic components:

    * A pre-mixing area or tank

    * A digester vessel or vessels

    * A system for using the biogas

    * A system for distributing or spreading the effluent

There are two basic types of digesters: Batch and Continuous. The Batch-type digesters are the simplest to build and are processed in small separate operations. The Continuous digester operates by organic material constantly or regularly fed into the digester. There are three types of continuous digesters: vertical tank systems, multiple tank systems, and horizontal tank or plug-flow systems.

The proper design, operation, and maintenance of continuous digesters can produce a steady and predictable supply of usable biogas. Many livestock operations store the manure they produce in waste lagoons, or ponds and a growing number of these farms are placing floating covers on their lagoons to capture the biogas which they use to run an engine/generator to produce electricity.

A biodigester usually requires manure from more than 150 large animals to be cost effective. Biogas production can also reduce overall operating costs where costs are high for sewage, agricultural, or animal waste disposal, and the effluent has economic value.

Europe, Australia and China have been using biodigestion for years. It is actually used in waste water treatment on large scale operations. Of course they are not dumping all kinds of chemicals and trash into their sewer systems. But with the EPA starting to regulate different types of emissions, the biodigester ends up being a win-win application of old technology and modern farm techniques.

http://www.chpcentermw.org/presentations/041103-IA/burns.pdf

http://www.anaerobic-digestion.com/html/anaerobic-digestion-process.php

http://www.cityfarmer.org/biogasPaul.html

http://www.anaerobic-digestion.com/html/wastewater_sludge_hydrolysis_w.php

http://www.manuremanagement.cornell.edu/Docs/Overview%20of%20AD%20for%20Dairy%20Farms%20-%20Wright%202001.pdf