September 03. 2012 9:00AM

Potawatomi digester to produce energy

Energy and the Environment

By Molly Newman

Milwaukee area food waste will be used to generate power in an anaerobic digester that will be built at Potawatomi Bingo Casino in Milwaukee.

The facility will be able to break down organic materials into methane gas, powering engines that will produce up to 2 megawatts of power. That adds up to about 16 million kilowatt hours per year, enough to power 1,500 homes, which will be sold back to Milwaukee-based Wisconsin Energy Corp.

“We will be producing the energy and selling it back to We Energies under a tariff agreement, which will then count toward their renewable energy portfolio standard requirements in Wisconsin,” said Jeff Crawford, tribal attorney general for the Forest County Potawatomi Community.

The energy production will offset most of the Potawatomi Community’s energy costs throughout the state, and also renew its commitment to the environment, he said. The tribe has about 17,000 acres of land throughout Wisconsin.

“For the entire tribe, it will not offset all of our energy needs for all of our facilities, but it’s a good chunk long-term of what we’re using right now,” Crawford said. “In order for us to completely produce our own green energy, it will have to be from multiple sources.”

The tribal elders, who use medicines from the woods, said the environment has been adversely impacted, probably because of the mercury in air pollution, Crawford said.

“As a government, we decided to do our fair share and protect and heal the Earth by producing green energy,” he said.

Last year, the Potawatomi Community installed 132 solar panels on its Milwaukee Administration Building. It has also reduced energy usage per gross square foot by almost 12 percent and corresponding carbon emissions by more than 20 percent since 2007.

The feedstock for the digester, like used cooking oil, food and beverage production waste and animal waste, will come from local sources, so there won’t be much transportation pollution involved.

“What we’ve learned over the last several years is if you are going to put in any green project on your land or related to one of your facilities, you have to look around and see what are the resources or the feedstock that are available,” Crawford said. “As it happens, in Milwaukee, there is a large amount of food and beverage waste product that’s readily available, which can be used for biodigesters.”

The $18.6 million project, undertaken by the newly-created FCPC Renewable Generation LLC, will include a 9,760-square-foot building on about 2.6 acres just west of the casino that is currently used for staff parking.

“If the operation is a success, there’s always a possibility of expanding it if necessary because the project’s been designed to be built in modules,” Crawford said. “We can scale it up or we can actually scale it back.”

The facility will be a negative air pressure environment, so odors don’t become a problem. Trucks will bring the organic materials into the facility in the form of liquid slurry, which can be easily pumped from truck to tank without a messy transfer process, said Bryan Johnson, renewable and sustainability leader at Titus Energy, which is serving as a consultant on the project.

“It’s all going to be pumpable material, so it’s going to be either slurried when we pick it up from a facility or there will be processing outside the facility to be able to accept this material in a slurry form,” Johnson said.

First, the slurry will be mixed in two smaller tanks to create the right recipe for the bacteria to produce methane gas. Employees will measure carbon, nitrogen, pH and other factors to hit the needed levels.

“Basically you mix them together and if you stay in a certain range, the chemistry in the digester is satisfied,” Johnson said.

Then, the mixture will be transferred to two tanks that are more than one million gallons each. Because of their enormous size, the tanks will be built on site.

Next, the slurry mixture will be heated to about 100 degrees and held in the tanks for at least 30 days so the bacteria can digest the organic material and create about 65 percent methane and 35 percent carbon dioxide, Johnson said.

The gas will be burned in on-site generators, using biogas engines manufactured at GE Energy in Waukesha, producing electricity.

It’s a highly efficient process, since 85 percent of degradable material is removed from the tanks and converted to energy, Johnson said. The solid byproduct from the digester will be sold as fertilizer.

The construction process will create 75 to 100 construction jobs at its peak. After the facility is completed, five people will work there full-time.

Rezoning and land parceling has been completed, and contractors have been chosen for the project. The tribe is currently in the design process ahead of an upcoming groundbreaking.

“It’s not shovel ready yet, but it’s getting closer,” Crawford said. “We’re hoping that sometime this fall, we break ground and then within 18 months or so, we’re up and running.”