aerial shot of sewage treatment plant

Low sulfur biodiesel produced from sewage enabled by beta-cyclodextrin

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Emeritus Professor Richard Parnas and his group at University of Connecticut Department of Chemical and Biomolecular Engineering developed a technology to improve a critical process of removing sulfur from biodiesel made from sewage. The technology is being implemented in a project at Danbury’s John Oliver Memorial Sewer Plant scheduled to go into operation in January 2023 that will convert fats, oils, and grease into biodiesel whose lifecycle emissions are more than 74% lower than petroleum-based diesel.

Brown grease has approximately 600 to 1000 parts per million sulfur in various molecular forms. The standard in the United States for biodiesel and other diesel fuels is 15 parts per million sulfur or less. In Europe and China, the standard is 10 parts per million. Consequently, 99% of the of the sulfur containing compounds must be removed.

At the plant in Danbury free fatty acids will be esterified with methanol to make fatty acid methyl ester, which is biodiesel. Then they trans-esterify any triglycerides in the mixture, as part of the process further cleaning the biodiesel to levels of around 200 parts per million sulfur – still not pure enough.

To purify the high sulfur biodiesel, many different types of filters and compounds were tested, with little success, until beta-cyclodextrin was chosen which worked effectively. Beta cyclodextrin is recycled making the process highly economic.

The Danbury plant is relatively small, treating around 10 million gallons of water per day, and the fat, oil, grease reclamation facility will make about 300,000 gallons of biodiesel per year. With hopes of expanding, involving three main hubs, one in Hartford, one in New Haven, and one other location in Connecticut, it would be possible to make approximately 10 million gallons a year of biodiesel with a raw material currently considered waste.

Cong Liu, Anthony A. Provatas, Richard S. Parnas:
Desulfurization of biodiesel produced from waste fats, oils and grease using β-cyclodextrin,
Separation and Purification Technology, Volume 305, 2023, 122417,

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