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Tech + EngineeringTech & Engineering

From Black Water to Green Energy

ByBrandon LevyNOVA NextNOVA Next

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Humans have spent the last two centuries largely dependent on environmentally damaging fossil fuels for power, so when Jeff Moeller attended a workshop discussing ways to replace some of this energy with more sustainable fuel made from algae, he was immediately intrigued.

An expert in wastewater systems and the director of water technologies at the non-profit Water Environment & Reuse Foundation (WE&RF), Moeller wondered if the same process could be applied to another wet, carbon-containing material: the sludge produced by wastewater treatment. After one of the workshop’s leaders confirmed his hunch, he wasted little time contacting a firm commercializing a promising technology, a U.S.-based company called Genifuel Corporation.

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Now, a public utility called Metro Vancouver now has plans to pilot a system based on the process to convert human sewage into oil and natural gas at its wastewater treatment plant in Annacis Island, British Columbia. Metro Vancouver chose to undertake the project after an independent assessment organized by Moeller and the WE&RF demonstrated the promise of the technology, which was developed by Genifuel in collaboration with the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL).

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Biocrude oil and liquid fuel

The Genifuel system combines two separate processes to transform wastewater sludge into fuel. The first step produces a type of oil called biocrude, while the second creates methane, the main component of natural gas. The two techniques are specific types of a procedure called hydrothermal processing, which uses high temperatures and pressures to produce useful products from wet materials that contain organic compounds, or substances made up of carbon. While hydrothermal processing has been around since the 1930s, recent improvements have made it potentially cost-competitive for the first time, said Corrine Drennan, who oversees PNNL’s bioenergy technology research.

Many wastewater treatment plants currently feed their sludge into an oxygen-deficient container called an anaerobic digester in which microorganisms turn some of it into biogas that can be burned for electricity and heat. But this only reduces the amount of sludge by about half, so the plant must pay to have the rest shipped to a landfill or incinerator. “In a big utility that can run into substantial money” said Jim Oyler, CEO of Genifuel.

The Genifuel system eliminates much more of the sludge, dramatically reducing the cost of waste disposal while producing potentially carbon-neutral fuel and clean, sterile water as practically the only byproducts. Moreover, while this process may not displace much fossil fuels on its own, PNNL and the National Renewable Energy Laboratory in Colorado are investigating other sources of liquid waste that could be turned into fuel. Oyler estimates that applying hydrothermal processing to easily accessible wet waste products like wastewater sludge, cow manure, and food processing waste could provide more than 15% of the U.S.’s liquid fuel by 2045, and adding in agricultural and wood waste could boost that figure even further. “It’s not going to be just one thing, but this technology could supply a substantial portion of our transportation fuels if fully implemented,” he said.

Oyler started investigating hydrothermal processing after several other successful business ventures, marking a return to the energy industry where he got his start. “Energy is the most fundamental physical process of all, and it is endlessly interesting,” he said. He sold his technology company and started Genifuel in 2006 with the goal of using hydrothermal processing to make biodiesel from algae. Hydrothermal processing’s ability to handle wet materials makes it more economical than other methods of converting organic matter into fuel because there is no need to spend money or energy drying the material first. But while Oyler’s goal proved technically feasible, it was too expensive to be practical.

Oyler then went searching for other substances his company could make fuel from, ultimately settling on wet waste products like wastewater sludge. “The advantage of processing wastes is that you do not incur the cost of growing and harvesting a crop such as algae,” he said. “Even better, some wastes—such as wastewater sludge—have a ‘negative cost,’ because the solids must be disposed of, and the disposal cost can become part of the revenue stream for hydrothermal processing.”

The WE&RF-organized independent assessment of Genifuel’s system was performed by PNNL under the supervision of engineers from technical consulting company Leidos, Inc. “The overarching goal was really to better assess if the technology does what [Genifuel] says it does,” Moeller said. “Can you produce biocrude oil from sludge, and what’s the composition of the different things that come out of there—the biocrude, the biogas, and the clean, sterile water?”

In PNNL’s bench-scale tests, Genifuel’s entire process reduced the amount of solids requiring disposal by up to 99 percent. The oil-generating step alone converted up to 37 percent of the sludge’s organic solids—the portion that could potentially become fuel—into biocrude, while virtually all of the remaining organic material becomes methane and carbon dioxide. The inorganic compounds like phosphorous and nitrogen in the sludge are the only ones a treatment plant might need to dispose of afterwards, although those two chemicals could be another source of income if they could be filtered out and sold as fertilizer, Moeller said. Moreover, if some of the nitrogen were filtered out, environmental regulations may permit the wastewater to be released into the environment without further treatment.

Genifuel’s system also produced natural gas free of certain silicon-based compounds that are a byproduct in anaerobic digesters. These siloxanes can damage engines, which forces utilities to clean the gas before burning it.

Bench-scale tests like those PNNL performed have significant limitations, and Oyler claims that these shortcomings caused the lab to understate the potential of his technology, which he says typically converts nearly half of the organic solids into biocrude instead of only 37 percent. In addition, because PNNL’s equipment was not designed for energy efficiency, it could not verify Genifuel’s claim that the fuel its system creates contains more energy than is required to make it.

Metro Vancouver hopes to answer that question with its industrial scale pilot. The utility’s Annacis Island facility, which treats the wastewater from more than 1 million individuals in 14 municipalities, will divert some of the sludge from its processing pipeline to Genifuel’s system and evaluate the results. Metro Vancouver will install the equipment for the oil-generating portion of the process after securing full funding for the pilot, which will likely occur by mid-2017, said Paul Kadota, Metro Vancouver’s program manager for utility research and innovation. The utility hopes to begin testing that part of the system by the end of 2018. Depending on its findings, it may later consider adding the second, methane-producing step.

Even if Metro Vancouver proves Genifuel’s claims, there are still economic hurdles to clear. Refining the biocrude into traditional fuels like gasoline and diesel could require expensive transportation unless it could be done economically on-site or nearby, said Dr. Timothy Strathmann, a professor and expert on hydrothermal processing at the Colorado School of Mines who is not involved with the Metro Vancouver pilot.

But if utilities are able to profit from hydrothermal processing of their sludge, Strathmann said, the financial and environmental incentives could dramatically alter wastewater treatment elsewhere. Metro Vancouver also sees great promise in technologies like Genifuel’s, according to senior media relations strategist Sarah Lusk. “Within the realm of wastewater treatment,” she said, “hydrothermal processing could be as dramatic as when the steam locomotive displaced the horse and carriage.”