HydroMentia, Inc.

A new frontier

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Source: HydroMentia, Inc.

While gas companies, universities, high-tech research firms, and even NASA have waded into the waters of algae-based biofuels, many wastewater utilities have stood along the shoreline watching others as they make the leap. But a few have realized the technology’s potential, growing algae at their wastewater treatment plants in order to remove nutrients.

They also convert these autotrophic organisms into biofuel that in the far-off future could be used to power the plants or commercialized to raise revenue for their operations.

Since September, the Rockaway Wastewater Treatment Plant in Queens, N.Y., has been engaged in such a project with the assistance of HydroQual Inc. (Mahwah, N.J.), Biohabitats Inc. (Baltimore), the University of Arkansas (Little Rock), and Blackrock Energy Corp. (Williamsburg, Va.). The New York City Department of Environmental Protection (DEP) invested $387,000 into the project, installing an Algal Turf Scrubber®, a patented technology that consists of two 100-m (350-ft) metal sloped troughs. One trough receives 150 L/min (40 gal/min) of effluent, while the other receives 76 L/min (20 gal/min). According to a DEP press release, the troughs’ design is meant to mimic a “stream ecosystem by varying flow currents and using sunlight to promote algae growth.” After sufficient algal growth occurs, usually within a 10- to 14-day time frame, the algae are gathered and the water is removed using wet–dry vacuums. The algae are shipped and converted into butanol by scientists at the University of Arkansas.

So far, the plant has produced 1 L of butanol.

“I know one liter doesn’t sound like a lot of biofuel, but it is, considering that it was made inside a lab with just lab equipment,” said Jamie A. Hestekin, an assistant professor of chemical engineering at the University of Arkansas. “The butanol that we gave them was fuel grade. You could probably run a car on it for about 8 miles [13 km].”

“As far as I know, no one else has made this much [using algae],” said John McLaughlin, director of ecological services at DEP.

Part of an overall plan

The project at Rockaway is part of the Jamaica Bay watershed protection plan, which includes upgrades at other wastewater treatment facilities in New York City, an oyster and eelgrass pilot restoration project, wetlands restoration at Paerdegat Basin, and green infrastructure projects.

When the department put together the watershed protection plan, it focused on “green technologies that had a big stormwater focus, but we were told that nothing was off the table,” McLaughlin said. So DEP decided to move forward with the algae project at Rockaway, he said, because it saw algae as a green technology that treated effluent and could be a source for renewable energy.

The contract was signed last summer, and the algal turf scrubber was operational from September to December.

“Right now we’re going through a seasonal shutdown,” McLaughlin explained.

Even though the algae can still grow in cold temperatures, it has gotten so cold in New York City that the ponds that feed the algal turf scrubber have frozen over.

At press time, McLaughlin had expected the plant to be back up and running by this month.

Not a simple formula

The process to convert algae to butanol can be complicated. “We’ve used two methods,” Hestekin said.

Scientists at the University of Arkansas have worked with a standard butanol technology that has been around for almost 100 years, and they have used a newer method that began in the 1990s. With the newer method, the anaerobic fermentation process to convert algae to butanol is broken down into two steps. The first, Hestekin said, is acid-genesis, whereby the starches and carbohydrates in the algae are hydrolyzed and extracted and then made into organic acids. Electrodeionization is used to extract pure butyric acid from this fermentation. In the second step, which is solvent-genesis, the organic acids are made into butanol.

Hestekin said a lot of algae are required to make a little butanol.

“Alga is about 85% to 90% water,” Hestekin said. The water is removed from the alga, and it is possible to do this by drying it on the turf scrubber. “Of the dry stuff, 15% to 40% is sugar. Of the sugar, 40% can be converted to butanol,” Hestekin said. “So keeping that in mind, if you had 100 pounds [45 kg] of wet algae, you would probably get about 1 to 2 pounds [0.45 to 0.9 kg] of biofuel out of it.”

But Hestekin also pointed out that this final product is still a lot compared to how much biofuel can be extracted by corn, another popular renewable fuel resource.

“Standard yield for corn to ethanol is 1 acre [0.4 ha] makes 330 gallons [1250 L] of ethanol per year,” Hestekin explained. “If you assume a growth rate on the algal turf scrubber system of 30 g/m2 day, the maximum yield of butanol is that 1 acre makes 1500-plus gallons [5700 L] of butanol per year. Since butanol is at least as good of a biofuel as ethanol, this means almost 5 times greater fuel production. That’s great, given that the algae on the 1 acre is also serving to clean up wastewater.”

Moving forward

McLaughlin said DEP plans to evaluate the algae biofuel project for the next 2 years to collect more butanol and improve the data. If it continues to have positive results, it may eventually expand it to other wastewater treatment plants within the system. But it has to keep in mind the geography of New York City and how it could limit the installation of the algal system at other locations.

“In most places where land is plentiful, you can build at any scale,” McLaughlin said. “But in New York, we can’t go farther out. We can only go up.”

McLaughlin said there also is maintenance to consider. “For the most part, the system is self-maintained, but there are occasional leaks, and there is pump wear and tear,” he said.

McLaughlin said for now the hope is to produce enough butanol to use it as an energy source to offset existing fuel costs at the Rockaway plant.

Hestekin said the team at the University of Arkansas also plans to continue to collect data, and it is pursuing other partnerships.

“We’re working with Statoil in Norway as part of a consortium with other universities, like William and Mary and the University of Maryland,” Hestekin said. “They are highly interested in the Chesapeake Bay and open-water areas.”

Hestekin said the team isn’t working with any other municipalities or wastewater treatment plants.

“New York is very forward-looking and thinking in this way,” Hestekin said. “They’re the only ones really doing this. As scientists, we’re used to having far-off ideas of how something can be taken to the next step, but DEP is very big into making this work and getting as much biofuel as possible.”

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