June 01, 2015

The Back Page: A Tale of Two Digesters

Jonathan Scoll

A Tale of Two Digesters

Huckabay Ridge was the largest anaerobic digester facility of its kind in the United States, with a total digester tank capacity of more than 7.3 million gallons, capable of converting organic waste into biogas and fertilizer. The gas was sold via pipeline to a California electric utility; the fertilizer was sold back to farmers.

Download a printable PDF of this article (membership required).

Its debut in 2006 promised a market-based manure management solution for the Stephenville, Texas, area, a farming community northwest of Waco. Nutrient pollution by cattle of Waco’s water supply had sparked litigation.

In 2010, its developer, Environmental Power Corporation, filed for bankruptcy and the plant was sold to EM Biogas, a subsidiary of Element Markets LLC of Houston. Still bullish, Element’s chief marketing officer, Randy Lake, declared success to be “more [about] chemistry than process engineering.” It turned out to be more about economics than either one.

By 2013, the plant was back on the auction block as EM Biogas “refocused its portfolio.” No doubt the plummeting price of natural gas played a role in its “refocus.”

Today, Huckabay Ridge sits idle in the scrublands outside of Stephenville. Its closure has impacted county property tax collections, school budgets, and area employment. Calls and emails to local officials, the town newspaper, and Element Markets for more information were not returned.

Planning for the Hometown BioEnergy project in Le Sueur, Minnesota, began about the same time as Huckabay Ridge started operation. Hometown’s developer is the Minnesota Municipal Power Association (MMPA), a consortium of twelve rural Minnesota municipalities. Each member operates a municipal utility in its community, purchasing electricity from MMPA, which both generates and purchases power for its members, who in turn serve retail customers.

Extensive “bench testing and piloting” was done with various waste feedstock combinations. The project, completed in 2013, is roughly half the size of Huckabay Ridge, with tank storage of 3.2 million gallons. Like Huckabay Ridge, it uses processes and equipment supplied by Xergi, a Danish company specializing in utility-scale combined heat and power and bioenergy digester systems.

Hometown’s feedstock includes livestock manure and waste from sweet corn and food processing. It produces biogas, liquid fertilizer, and a solid material sold for livestock bedding. But the resemblance between the two projects ends there.

Instead of selling biogas, Hometown BioEnergy uses it to generate electricity supplied directly to the City of Le Sueur. Biogas is stored onsite, and the facility’s generators can be dispatched as daily load and market fluctuations dictate.

Hometown helps MMPA achieve compliance with Minnesota’s aggressive renewable energy standards. Legislation adopted in 2007 will require 17 percent of retail energy in Minnesota to be from renewable generation by 2016, increasing 25 percent by 2025.

As a public entity, MMPA is in bioenergy for the long term and can accept slimmer margins than many private investors. “If this were a for-profit entity outside the utility industry,” says Kelsey Dillon, vice president of Avant BioPower, which developed and operates the facility, “you’d likely need a nearby entity with a severe waste stream problem to make it work.”

Jonathan Scoll

Jonathan Scoll is a member of the editorial board of Natural Resources & Environment.