Biodigesters: environmental friend or foe?

May 1, 2023

4 minutes, 18 seconds read

Biodigesters: environmental friend or foe?

As food waste has increasingly become a government priority and subject of public interest, there has been greater movement to identify environmentally friendly alternatives to landfill disposal. In the landfill, food waste breaks down in an oxygen-free process that releases damaging levels of methane as a byproduct. Preventing this food from entering landfills is the most effective strategy for limiting methane emissions. However, as localities evaluate solutions for disposing of food waste, many have evaluated the potential of biodigesters as well as digestion facilities. 

Biodigesters and anaerobic digestion facilities are both solutions for breaking down food waste, but the differences far outweigh the similarities. The most critical difference, however, is that only one of these solutions has the ability to continue to put dangerous levels of methane into the atmosphere. 

Understanding anaerobic digestion of food waste

Food waste is a big problem, and it seems to require a big solution. This is where anaerobic digestion of food waste seems like the ideal fix. Anaerobic digestion tends to happen in large tanks or facilities at municipal landfills or at agricultural sites. Within these massive biodigesters, organic waste is broken down in an oxygen-free process, just like the process occurring within landfills. The difference here is that anaerobic digestion facilities aim to capture this methane and other gasses – together called biogas – and use it for energy. That biogas can be used to heat buildings, converted to electricity or, through additional processing, serve as pipeline-quality renewable natural gas.  

It’s a pretty exciting possibility, that of turning waste into fuel. But existing anaerobic biodigesters highlight many of the problems with this approach.

Environmental concerns around anaerobic digestion of food waste

It turns out, it takes a lot of organic matter to create biogas. In fact, it requires so much organic matter, and in such a wide variety, that many facilities source crops that are grown specifically for the purpose of serving as an energy feedstock rather than a food source.

This creates new demands on land and water, and exacerbates greenhouse gas (GHG) emitting agricultural practices, to achieve an end that is intended to prevent excessive crop production. 

Then, there is also a need to transport waste and feedstock to these sites, which further increases GHG emissions.

It also leads to increased traffic, and odors, for the individuals who live near these sites.

Then, there is also a need to transport waste and feedstock to these sites, which further increases GHG emissions. It also leads to increased traffic, and odors, for the individuals who live near these sites. It’s why one proposed multimillion-dollar biodigester facility in Foothills County, Alberta, Canada, has seen opposition from county residents. The Western Producer reports that the facility aims to turn feedlot manure and grocery store food waste into fertilizer and renewable natural gas. However, it may potentially be transporting manure from multiple nearby lots to support biogas production.

A proposed facility near Scotland’s Easter Airfield faces the same issues. The application projects an estimated 65 vehicles movements each day, including 18 tankers, to support the anaerobic digestion of food waste. In responding to the proposal, the local residents cite lessons gleaned from another nearby biodigester. In addition to the unpleasant odor released by the facility, residents have expressed concern about notices warning of the potential for explosive atmospheric conditions and the need to flare uncollected biogas. 

That last point is perhaps the most problematic part of this solution. The systems used to capture this methane are not fully efficient currently. For example, the U.S. Environmental Protection Agency estimates that a landfill gas project may capture anywhere between 60% to 90% of the emitted methane. Much of the remaining methane escapes to the atmosphere or continues is burned off in a process that releases carbon dioxide. 

Breaking down the differences between biodigesters

Given the potential drawbacks of biodigesters, it’s easy to understand the apprehension in adopting a creative approach to food waste disposal. However, it’s important to understand that not all biodigesters operate in the same way.

The important distinction between them is oxygen. 

An aerobic biodigester is a sealed piece of equipment designed to break down organic waste in an oxygen-rich process.

Through the introduction of waste, water, and microorganisms, a wide variety of food waste can be quickly broken down.

Aerobic biodigesters have a small footprint so that they can be located where food waste is generated, within a kitchen or food production area.

This eliminates the need to transport waste offsite. As the equipment is sealed, it also eliminates the potential for odors. The byproducts of aerobic biodigesters include a sewer-safe grey water that can be disposed of safely down the drain or used in landscape irrigation. 

So, environmental friend or foe?

There is a world of difference between anaerobic biodigesters and aerobic biodigesters. While anaerobic biodigesters may have value in agricultural applications where methane capture solutions are critical, there are better alternatives for food waste disposal.

To learn more about the benefits of an aerobic biodigester, or to find the solution right for your site, discover the range of Power Knot’s LFC Biodigesters.