The Anaerobic Digestion Process

What is Anaerobic Digestion? 

Anaerobic digestion is a biological process that occurs in nature – most commonly in the stomachs of animals. In the simplest terms, it is the process of bacteria consuming (digestion) organic waste in an oxygen-free environment (anaerobic) and producing natural gases as a result.

This graphic from the American Biogas Council depicts the basic process of anaerobic digestion.

The environmental benefit of the anaerobic digestion (reduction of waste and natural gases released by landfill waste) has led to a growth in development of municipal and commercial biodigestion facilities around the world. Common uses include biodigesters on farms, at wastewater treatment facilities and near sites where large amounts of food and other organic waste are produced. These facilities can recycle waste to be used for:

  • Harvested Methane
  • Compressed natural gas used in vehicles
  • Heat

This chart shows the best sources of waste for clean and efficient energy production.

What are Biodigesters? 

Biodigesters take organic waste material – whether it’s the leftovers of a school lunch, the solid grains used to make distilled bourbon, or wastewater at a treatment plant – and use it to create renewable energy.

How is this possible?

Decaying waste materials naturally produce gas, most of which is methane. Biodigesters efficiently accelerate the decaying of organic waste and collect the methane to make energy. The solids that are left over make great fertilizer too!

Harvesting Biogas

Feedstock is loaded into a sealed module and digested on an anaerobic basis.

  • Liquid (the “percolate”) containing methane-producing microbes is continuously recirculated throuught the biomass and into the reactor tank for biogas generation.

Biogas is harvested, filtered and piped into the existing gas distribution system.

After the conclusion of the methane production period, the biomass (the “digestate”) is composted within the same module.

  • The digestate is never exposed to the environment.
  • Air is drawn into the modules creating ideal aerobic conditions.
  • The digestate is converted into a high quality compost and soil amendment.

Where are Biodigesters?

Biodigesters, which turn food and other organic waste into renewable energy, are being used safely and effectively in thousands of communities and neighborhoods around the globe. In some countries, it’s common for apartment buildings to have their own biodigesters.

In the United States, businesses, universities and communities are increasingly turning to biodigesters to limit the amount of food waste sent to landfills. Ideally, biodigesters are located close to the source of food waste – reducing truck traffic and other impacts.

From “The Most Magical Place on Earth” to nearby neighborhoods, here are some examples of biodigesters at work:

Louisville’s Own Backyard – In the Louisville area, several biodigesters have so little impact on neighbors that they’ve received almost no attention. The ConAgra biodigester in Oldham County is located next door to the local YMCA and a residential neighborhood. In West Louisville, a biodigester at the Morris Forman Water Quality Treatment Center produces some of the energy needed to run the facility.

Walt Disney World – Just a mile from Walt Disney World in Orlando, a biodigester collects energy from the food waste left by Disney’s 17 million annual visitors. Follow this link for more information.

The University of California-Davis – A campus with 26,000 students has one of the largest biodigesters on a U.S. college campus, converting 50 tons of waste into 12,000 kWh of renewable electricity. Follow this link for more information. 

Concord Hilton in the San Francisco Bay Area – A 320-room luxury hotel at the gateway to Wine Country has a working biodigester in its kitchen. Follow this link for more information. 

Brooklyn neighborhood – Artistically-lit, egg-shaped biodigesters are located in a densely populated New York neighborhood. They have become local landmarks while recycling waste water, reducing food waste and producing clean energy. Follow this link for more information. 

Click here to see a list of projects profiles from across the country.

Frequently Asked Questions 

Who is Star BioEnergy?

Star BioEnergy is investing in clean energy technologies. The company, which is owned by Star Energy Holdings, is developing state-of-the-art recycling facilities that harvest natural gases from food waste and other bio-waste, so it can be used as an alternative source of energy. 

We currently have projects underway across the United States. 

Who is Star Energy Holdings?

Star Energy Holdings is a company focused on developing energy from cleaner, renewable sources such as wind, solar and waste-recycling technologies. The company is based in Fort Wayne, IN., and led by a management team with decades of experience developing alternative energy projects. To learn more about Star Energy visit our parent company website at 

How does your company fit into national waste and environmental initiatives? 

A White House report on the need to reduce methane emissions listed biodigesters as a way of capturing and using methane that would otherwise be released from landfills into the atmosphere as a greenhouse gas. Meanwhile, the USDA and the EPA have joined forces to promote the National Food Waste Challenge – a campaign aimed at reducing the amount of wasted food. The EPA says that “if 50 percent of the food waste generated each year in the U.S. was anaerobically digested, enough electricity would be generated to power 2.5 million homes for a year.” 

Part of the mission of Star BioEnergy and its parent company, Star Energy is to provide sustainability through active renewables. Identifying, developing and building anaerobic digesters, we’re taking the wasted food that would otherwise be in a landfill and turning it into a much-needed renewable source of energy. 

How new is this technology? 

In 1859 the first known anaerobic digester was built in Bombay, India. Four decades later the technology was developed in England, where a septic tank was used to generate gas for the sewer gas lamp, a type of gas lighting that eliminated noxious sewer odor.

In recent decades technological advances have made the process cleaner, more efficient and practical. Star BioEnergy is (working with/partnering with technology) to develop anaerobic digesters as a renewable energy source in the U.S. 

Is the technology proven? 

The technology has become common worldwide. There are 10,000 operating digesters in Europe and over 2,100 sites producing biogas in the U.S., located anywhere from local farms to wastewater treatment plants. Among these wastewater treatment plants equipped with anaerobic digestion, 860 are using the biogas they produce. The potential for growth in the U.S. is huge. India, China and a few Western European countries have been using anaerobic digesters for decades. 

Other Resources

More information about the growing use of anaerobic digesters is available at these links: