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RICHMOND, Va. – “It’s free cooking gas”, said Monica Alinea.

Monica Alinea and her husband, Tim, are proud owners of a HomeBiogas system.

Located in the sunny backyard of their Pensacola, Florida home, the system looks like a 7-foot rectangular black ball. But it’s not inflated with air, it’s methane.

The Alineas use HomeBiogas, a product that turns household food waste into cooking gas through a composting process called anaerobic digestion. The product became commercially available in 2016, according to the HomeBiogas website.

Shakira Hobbs is an assistant professor of civil engineering at the University of Kentucky and did her postdoctoral research at the University of Virginia. Hobbs studies sustainable environmental engineering and compares anaerobic digestion to the human digestive system.

“If I eat an apple, I chew it and break it into small pieces, then it goes down my esophagus and eventually into my stomach,” Hobbs said. “I have these natural enzymes that will further break down that food waste and process it through my digestive system (to) produce two things, a solid and a gas.”

The Alineas take food waste, like vegetable scraps or banana peels, and feed it into the anaerobic digester through a tube. The waste is collected in a large chamber, and within hours the microorganisms in the chamber begin to break down the food waste, releasing methane gas. The gas rises and collects in a flexible tank and can be piped directly into their kitchen to power a stovetop burner, providing them with free cooking gas.

The Alineas are part of a growing group of home chefs and passionate gardeners in the country who seek self-reliance and use food waste to fight climate change.

“We hate wasting stuff,” Tim Alinea said, “and we knew our leftover food could be put to good use.”

Environmental impact of methane

The Environmental Protection Agency reports that carbon dioxide and methane are the more abundant greenhouse gases emitted by human-influenced actions. This can have an impact on global temperaturesalters weather patterns and contributes to human health problems.

But methane can be 25 times more powerful than carbon dioxide to trap heat in the atmosphere, so reducing methane emissions could have rapid and significant positive effects. Landfills are the third largest source of methane emissions in the United States

“Composting produces methane,” said Bruno Welsh, founder of Compost RVA“but it produces a lot less methane than a landfill.”

the EPA estimates that in 2018, the most recent year for which data is available, US households generated 25 million tons of wasted food; 66% was landfilled while only 3% was composted. The rest went to waste water management or combustion services.

When food waste is landfilled, it breaks down with inorganic materials like plastic and metal. Consider a kitchen trash bag. Airflow is diminished and food rots, slowly releasing methane into the atmosphere.

But once captured, methane can become a form of renewable energy called biogas. It can be converted into electricity or used as fuel for cooking and heating.

“We can produce [BioGas] in about ten days, depending on substrates and conditions,” Hobbs said. This contrasts with natural gas, a commonly used form of non-renewable energy, which could take millions of years to form.

Advantages of domestic biogas

Zak Dowell’s suburban home is in the hills of Blacksburg, Virginia. Dowell, who has a background in building science and environmental design, is a Virginia Tech BioBuild researcher on anaerobic digestion systems for home use. He has built several anaerobic digesters in his backyard over the past decade, but he also purchased a HomeBiogas system a few years ago.

“I have a 6,000 watt solar system on my house,” Dowell said, “but I do more of my part for the environment by sorting my food waste and disposing of it responsibly.”

Dowell composts diligently for her family of four and hasn’t thrown away a piece of food in nearly 15 years.

Dowell considers anaerobic digestion as an eco-innovation. Most anaerobic digestion users report spending several hours a week fueling and maintaining backyard digesters.

For those interested in anaerobic digestion, it is possible to build a system using commonly found hardware supplies. HomeBiogas produces a system for residential and backyard use.

The basic HomeBiogas system costs less than $1,000 and can generate up to two hours of cooking fuel per day, according to its website. But this delay depends on other factors, such as the climate and the regularity of the power supply to the system. Warm weather allows for faster decomposition and the creation of methane.

“HomeBiogas is for Florida; you can drop this thing in hot weather, and it will produce gas, it’s an awesome product,” Dowell said. But people in northern climates of the United States may be limited to using a digester only during the warmer months or may be forced to build a greenhouse to maintain high temperatures during the winter.

Michael and Britney Maness live on a 6-acre farm in Puerto Rico and use renewable energy, including solar power and biogas.

“I love drinking tea every day and I don’t have to feel bad to boil water anymore,” Brittney Maness said with a laugh.

She grows her own tea and uses biogas to cook, which is a sustainable way to do something she loves, Maness said.

By-products and limits of anaerobic digestion

The EPA explains how anaerobic digestion digestate product, which is a biofertilizer or an effluent. When considering the analogy of the human digestive system, it would be the “solid that we all produce,” Hobbs said.

“A big plus is the biofertilizer,” Mike Maness said. “This stuff is really good for the plants.”

The Manesses have a passion for horticulture and have seen a significant improvement in their crop yields since using digestate.

But for households without a robust vegetable garden or small farm, the biofertilizer can turn into buckets of sludge that must be treated.

Some municipal wastewater facilities and large farms in the United States have been producing biogas and digestate for decades.

When Roy Vanderhyde installed an anaerobic digester on his southwest Virginia dairy farm in 2008, he wanted to use the digestate as pathogen-free bedding for his animals. But he soon found value in biogas.

The only input to the digester was manure and the biogas was converted on site into electricity. Vanderhyde’s electric bill was $13,000 a month before the digester, he said.

“(It) produced enough electricity that I didn’t have an electric bill,” Vanderhyde said. “Plus, I would sell enough kilowatts for the average 300 homes.”

The Central Marin Sanitation Agency in Northern California is a sewage treatment plant which operates two 80-foot anaerobic digesters. The biogas is transformed onsite into electricity and powers the facilities an average of 19.3 hours per day, according to the agency’s Green Business Report for fiscal year 2021. The digestate is processed and used locally as fertilizer and daily landfill cover. .

Food waste from local restaurants and grocery stores was added to the agency’s digesters in 2014. The agency now accepts nearly 6 tons of food waste every day. The digesters produced about eight hours of electricity a day before the food waste was used, less than half the energy they currently produce, according to general manager Jason Dow.

But anaerobic digestion has other disadvantages besides digestate management. Systems often have complicated parts that might require sophisticated engineering to troubleshoot. Residential users, such as Alineas, cite the time spent powering the system as a limitation. The Manesses find that the system is water-intensive.

Posters on the HomeBiogas system owners Facebook group frequently visit the page to troubleshoot system issues. Homeowners have experienced leaks, insufficient methane production, difficulty inoculating new systems, and pH imbalance, according to user posts. Since HomeBiogas is headquartered in Israel, it may take time for Americans to receive new parts, according to some US users.

Technical obstacles are not isolated for people who practice anaerobic digestion in their garden. One of two digesters at the Marin County Wastewater Treatment Facility experienced an outage in 2021 that interrupted power generation for more than six months, Dow said.

The preformed concrete dome of Vanderhyde’s digester collapsed in November 2017 due to sulfuric acid buildup, according to Vanderhyde. It ended his nine-year renewable energy production and sparked a four-year legal battle with his insurance company over whether the system was covered.

Despite the potential shortcomings, experts and users like Dowell still find the technology magical.

“Being able to see something that’s considered waste…being able to produce energy was an eye opener for me,” said Hobbs, who first learned about anaerobic digestion in college. .

Hobbs has since earned a doctorate in the field of sustainable environmental engineering and started a non-profit organization called BioGals, which aims to empower women of color and engage communities to co-create solutions for a more sustainable world. According to its site, a major project for the organization is the construction and implementation of anaerobic digesters.

By LARIN BRINK
Capital News Service, Virginia Commonwealth University

Capital News Service is a program of the Robertson School of Media and Culture at Virginia Commonwealth University. Students in the program provide state government coverage for a variety of media outlets in Virginia.