What Is a Biogas Generator?

A biogas generator is a machine that generates electricity using biogas as fuel. At least, that’s one kind of biogas generator, and it would be a handy piece of equipment if you had enough biogas to operate it. But to produce that gas, you need a different type of biogas generator, known in the energy industry as a biogas digester.

Biogas digestion isn’t an exotic concept. Septic tanks, landfills and our own bodies — as well as the bodies of all creatures that digest organic matter for survival — are biogas digesters. They are all closed systems in which bacteria break down organic compounds in an anaerobic (oxygen-free) environment and release gases, some of which are flammable and can be used as fuel.

What turns a digester into a biogas generator is an airtight piping system that collects and store these gases rather than letting them dissipate into the atmosphere. Today, 90% of the world’s biogas comes from China, the United States and Europe — mostly Germany — and about two-thirds of it is used to generate electricity and heat.

Collecting and burning biogas addresses two pressing global environmental problems: It combats global warming by sequestering greenhouse gases and it provides a source of renewable energy.

What Is Biogas?

Biogas is a mixture of gases produced during the anaerobic digestion of organic matter in an oxygen-free environment. It’s mostly a mixture of methane and carbon dioxide with traces of other gases, such as hydrogen sulfide and ammonia. Biogas can be processed to separate methane from carbon dioxide and other non-combustible impurities and make biomethane, a renewable natural gas.

What Is a Biogas Generator?

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Here are some examples of biogas generators ranging from home-size to industrial:

• A sealed-compartment digester consists of a tank into which the user introduces organic material for digestion and an airtight system of pipes and holding tanks to store the gases which are generated. A septic tank would qualify if it was connected to the requisite gas retrieval piping system, and so would a yard-waste and food-waste composter.
• A larger-scale system traps gases released from landfills and stores them in tanks for use as fuel for large industrial generators. In 2018, biogas generators in Germany, the U.S. and the United Kingdom produced about 18 gigawatts of electrical power from biogas, and up to that point, production had increased by four percent per year since 2010.
• A wastewater treatment plant collects and stores gases from wastewater and sewage.

A biogas generator can also be a generator that runs on biogas, and such machines do exist. In fact, any home generator that runs on natural gas can probably burn biomethane. Large-scale natural gas generators, such as those offered by Caterpillar and other manufacturers, are designed to be combined with biogas digesters. In theory, you can feed biomass like manure and plant material into one end and get electricity from the other.

Pros and Cons of a Biogas Generator

Biogas is a clean-burning fuel that homeowners could potentially use for cooking and heating. The environmental benefits of producing biogas with a digester and using it as a substitute for natural gas include:

• Cleaner air. The digester traps and recycles gases that would add to the climate problem. Methane in particular is a more potent greenhouse gas than carbon dioxide.
• Clean, usable compost. The nutrient-rich byproducts of a biogas generator can be worked back into the soil.
• Sustainable and renewable energy. Once the digester is set up, all the biogas it produces is free, and because waste is continually produced, it’s a long-term energy source.

The main drawback of biogas digesters is that there just aren’t that many available for home use. I found one on Amazon for almost $800, and it’s basically a compost barrel with a gas collector; the product carries a disclaimer that the gas isn’t “a consumable item like other commodities.”

Even if you do find a system to purchase that can safely store large amounts of biogas, the methane you want still has to be separated from the other gases to burn efficiently. Also, the gas has to be pressurized before you can feed it into your stove, your heater or your biogas generator, and the digester must have leak-proof connectors. Products that address these problems are hard to find.

A Biogas Generator Is a Good Option If…

A system that generates biogas is useful only if you have enough biomass to make it work. A typical single-family residence doesn’t produce enough waste to make a biogas generator practical, but a large community in which everyone participates in the maintenance of the digester might. Biogas digesters and generators can also work well on farms with plenty of manure and vegetative waste to feed it.

Municipal and other collective operations that collect gases from landfills and sewage plants and burn them in industrial-size generators have the best chance of success. At present, only a fraction of one percent of grid electricity comes from biogas, but that number will likely grow as technologies develop.