Advanced BioFuels USA

by Asanga Padmaperuma (U.S. Department of Energy) Techno-economic analysis is the first to model PNNL technology across wastewater facilities — Wastewater—American households produce billions of gallons of it daily, from flushing toilets to cleaning clothes. But wastewater is not just a waste. The energy, nutrients, and metals contained in the untreated sludge at thousands of the nation’s wastewater resource recovery facilities have the potential to be transformed into a renewable, cost-effective feedstock for liquid transportation biofuels.

A team of researchers from the Pacific Northwest National Laboratory (PNNL) conducted a techno-economic analysis to investigate how cost-effective it would be to use a newer process—hydrothermal liquefaction, or HTL— for treating wastewater solids by converting them to biofuels. By modeling the long-term economics, they found that HTL can be economically deployed at more than 1,000 wastewater resource recovery facilities, where it can convert more than three-quarters of untreated sludge solids into biocrude. The biocrude immediate, which is similar in appearance to petroleum crude oil, can be used directly or upgraded in a refinery to a variety of liquid transportation fuels.

The analysis, which was supported by the U.S. Department of Energy’s Bioenergy Technologies Office, is summarized in the Journal of Environmental Management.

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The PNNL-developed HTL process is an efficient thermochemical waste-to-energy conversion technology that can rapidly convert solid sludge and other biosolids directly into versatile biocrude. The technology benefits the wastewater sector because it is more efficient at destroying solids and recovering carbon than traditional sludge treatment processes and creates a new source of revenue—fuel sales—that helps offset costs and improve environmental services.

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The team also determined that integrating HTL into the existing fleet of treatment facilities could increase total national energy recovery from wastewater sludge by 188% and reduce total disposal biosolids costs by 43%—or $1.4 billion per year—from current practice.

Compared to anaerobic digestion, HTL has the potential to:

• Recover more carbon than biogas production
• Achieve greater reductions in treated wastewater solids mass
• Replace a sensitive biological process with a reliable chemical reaction
• Reduce reliance on land application, landfilling, and incineration.

Simultaneously reducing sludge management costs while producing a valuable liquid fuel could help HTL have significant positive impacts on wastewater treatment sector economics and operations.  There may even be synergies between HTL and anaerobic digestion, which researchers are currently exploring.

In addition to sharing the news about next-generation conversion technologies with municipalities planning large capital investments or designing new treatment facilities, the team plans to investigate the potential financial and environmental benefits of blending wastewater solids with other wet organic wastes, such as manures, food waste, fats, oils, and greases to support very large biorefineries across the nation.     READ MORE

Municipal wastewater sludge as a renewable, cost-effective feedstock for transportation biofuels using hydrothermal liquefaction (Journal of Environmental Management)