Waste morphs into energy: More methane could reduce costs

Waste morphs into energy: More methane could reduce costs

Dec 9 - McClatchy-Tribune Regional News - Don Behm Milwaukee Journal Sentinel

Sun seekers and swimmers put off by slimy, foul-smelling cladophora algae covering Lake Michigan beaches and rocky shorelines in summer have a pair of new allies in the ongoing battle with the nuisance plant: Daniel Zitomer and hungry microbes.

Where some see a putrid eyesore, Zitomer sees a sweet opportunity to make energy.

Allow bacteria and other microbes known as archaea to digest the stringy algae in enclosed tanks and the end product is methane, said Zitomer, an associate professor of engineering and director of the Water Quality Center at Marquette University.

The same goes for animal droppings at the Milwaukee County Zoo, as well as waste from food processing, candy making or even distilling liquor. Each is rich in organic carbon compounds, and they, too, could yield methane if digested by a diverse set of microbes.

Then, Zitomer says, burn the methane to generate electricity to lessen demand for energy from coal or natural-gas-fired power plants and reduce emissions of carbon dioxide and other gases from the power plants that could contribute to global warming and climate change.

The tanks and microbes he wants to fill with cladophora and organic wastes from the community are at the South Shore Wastewater Treatment Plant in Oak Creek.

The Milwaukee Metropolitan Sewerage District uses bacteria and archaea to digest human feces and other sewage solids removed during the beginning of the treatment process at the Jones Island and South Shore plants. The blend is mixed and heated in four separate tanks with capacities of 3 million gallons each and two smaller tanks with half that capacity at South Shore.

Nearly a decade ago, Zitomer identified a seasonal waste -- aircraft de-icing fluids from Mitchell International Airport -- that could be poured into the digesters to boost methane production.

Christmas will come early again this year for billions of bacteria and other microbes in the below-ground tanks at the South Shore plant. The winter's first tanker full of de-icing waste -- propylene glycol and water -- arrived last week.

The addition of glycol to the tanks has the same effect as tossing sugar-loaded candy to children: It sets off a feeding frenzy among bacteria and archaea, Zitomer said.

Glycol molecules are broken apart by bacteria, then quickly fermented into acids, which are converted to methane by the archaea. Both groups of microbes working in the tanks thrive in warm, oxygen-free environments.

Since 2000, the airport has shipped between 250,000 and 300,000 gallons of the waste each winter to the South Shore plant. Tankers arrived more frequently last winter, however, and the treatment plant received a record 500,000 gallons.

In October, a separate partnership between InSinkErator, the Racine-based maker of food waste grinders, and Outpost Natural Foods on S. Kinnickinnic Ave. started sending small volumes of ground vegetables to the digesters at South Shore.

In 2007, the total energy value of methane produced in the digesters was estimated at $1.9 million, MMSD chemical engineer Jeff Schilling said. That dollar figure equals the money MMSD saved by reducing energy purchases for the plant. No estimate was available on the value of methane provided by adding the de-icing waste, he said.

The district still needed to buy $1 million worth of electricity for its South Shore plant last year, Schilling said. Electricity primarily operates pumps in the treatment system and lighting at the plant.

MMSD also bought nearly $675,000 worth of natural gas for South Shore in 2007. Natural gas is used to heat buildings there and is burned in engines that run large air compressors for one step in the sewage treatment process.

Methane created in the digesters is burned to run some of the air compressors and to generate electricity.

Creating more methane would further reduce MMSD energy costs in future years, according to Peter Topczewski, MMSD's water quality protection manager.

"There is plenty of capacity in our digesters for more waste to make more methane," Topczewski said.

The district's commission has agreed to spend up to $150,000 for Zitomer's next search for wastes that can further boost methane yields in the tanks.

We Energies has contributed $157,894 to the project along with $28,000 from Veolia Water Services, the private company hired to operate MMSD treatment plants, deep tunnels, the Milorganite factory and regional collector sewers. Marquette has committed $30,000.

Beginning in January, Zitomer will identify as many as 15 types of waste to be tested for potential yields of methane and for contaminants that might harm South Shore's microbes. The four top options will be fed to digester microbes in small, laboratory-size containers to confirm the earlier methane analysis before any of the wastes are poured into the tanks at South Shore for testing.