Biodigesters: good or bad for the environment?

September 26, 2022

3 minutes, 54 seconds read

Biodigesters: good or bad for the environment?

Digesters have emerged as a popular, environmentally friendly choice for managing food waste. In fact, some states are investing millions into these digesters. However, other states are levying millions in fines against digester operators accused of polluting their environment. 

How can the same technology get two such very different reactions? 

One reason is that the promise offered by digesters—of breaking down organic material using natural, bacteria-rich processes—has at times been overstated. The other, far more impactful reason, is that there are two distinct types of digesters, with two very different environmental impacts. 

Know the different biodigesters 

The two different types of digesters are anaerobic digesters and anaerobic biodigesters. Aerobic means “relating to, involving, or requiring free oxygen,” and it’s the presence (or absence) of oxygen in the decomposition process that makes a critical difference in output. 

  • An anaerobic digester breaks down organic waste in a process that does not use oxygen. This biodigester is a sealed piece of equipment and often a large facility located at a municipal landfill, agricultural site, or other large producer of organic waste. The byproducts of an anaerobic biodigester include digestate, the liquid and solid waste left after digestion, and biogas, which is mostly the greenhouse gas methane. 
  • An aerobic biodigester breaks down organic waste in an oxygen-rich process. This biodigester often can be located within a kitchen or food production area. The byproducts of an aerobic biodigester include carbon dioxide and a sewer-safe gray water that can be disposed of safely down the drain or used in landscape irrigation. 

So, what’s the problem with digesters? 

Since at least the 1970s, anaerobic digesters have been touted as a solution—not so much for mitigating the problem of organic waste as they often are today, but as a potential fix for energy challenges. That’s because the potentially dangerous methane and other biogases emitted by anaerobic biodigesters is captured and used to provide heat or generate electricity. However, excess methane is regularly flared off, or burned and released into the atmosphere, to release pressure on the digester system. There is typically no measurement of how much methane may be flared, as there is no requirement to monitor this. 

However, not flaring off this excess gas is a direct violation of Environmental Protection Agency regulations. It’s also one of the reasons Ohio anaerobic biodigester operator Renergy is currently embroiled in multiple lawsuits. In June 2022, a lawsuit filed against the biodigester in Bath Township, Ohio, cited foul oders emitted by the facility. Those lawsuits further named the U.S. EPA and Ohio EPA, reports, alleging that the agencies failed to enforce the Clean Air Act. Following those allegations, the U.S. EPA determined that the biodigester was in fact in violation of EPA permits due to not running its flare to burn off excess gas in more than a year, despite processing incoming feedstock.

A citizens group representative told that the group was concerned biosolids produced by the facility and sold to local farmers as fertilizer may not have met EPA safety standards, with potentially harmful impact to crops and consumers.

Meanwhile, in Sept. 2022 the state of Ohio identified potential violations at Renergy’s site in Morrow County, Ohio. A court filing alleged that the facility was improperly storing nearly 1.5 million gallons of untreated organic waste, leading to high risk of leakage and pollution.

The high cost of oxygen-free digesters

Smelly, high risks of pollution, and unsafe… these are frequent descriptors of anaerobic digesters by the communities in which these facilities are located. With this bad publicity, there’s an increasing belief that these digesters create more environmental problems than they address. That’s because organic waste only emits methane when sealed within landfills or reactors like those used for anaerobic digestion. Despite the complaints, these facilities are typically subsidized by federal or state funding, at high cost to taxpayers. 

Fortunately, many large organic waste producers are discovering that there is an alternative to anaerobic digesters. Aerobic biodigesters are gaining in popularity because they offer a truly environmentally friendly solution to organic waste disposal. Moreover, this equipment is incredibly convenient. Rather than contracting a waste management company to transport organic waste separately, organizations can install this solution right in their food prep area. 

Aerobic biodigesters have oxygen input, keeping methane out of the equation, and generating no bad odors. 

Curious to learn more about how aerobic biodigester can help your organization manage food waste and reduce your carbon footprint? Visit our Center of Sustainability for more insight on aerobic biodigesters or contact Power Knot with questions.