LF wastewater pretreatment facility near ethanol plant refurbished

Suspension of ethanol plant activities offered the perfect opportunity

By Terry LehrkeNews Editor

More than 1,600 diffusers provide air for the biological bacteria that feed on the organic matter in the water from the Central Minnesota Ethanol Co-op north of Little Falls. All of the diffusers were replaced when the wastewater pretreatment facility was refurbished.

More than 1,600 diffusers provide air for the biological bacteria that feed on the organic matter in the water from the Central Minnesota Ethanol Co-op north of Little Falls. All of the diffusers were replaced when the wastewater pretreatment facility was refurbished.

The wastewater pretreatment facility next to the Central Minnesota Ethanol Co-op north of Little Falls, has been refurbished.

The city of Little Falls found September was a good time for the project, since the plant had temporarily closed its operations and the facility was not being used.

The ethanol plant went back online Monday, just after the work had been finished.

The facility, built in 1997, treats wastewater that comes from the ethanol plant — about 110,000 gallons of the 350,000 gallons of water the ethanol plant uses each day.

It has two tanks that are about 100 feet in diameter and 20 feet deep that hold 1,600 diffusers that produce tiny air bubbles.

The oxygen in the air bubbles is needed to keep bacteria alive and growing. The bacteria actually cleans the wastewater from the ethanol plant.

“Bacteria requires oxygen and organic matter to eat. You need oxygen to break down the organic matter and the air is actually used to mix the bacteria with organic matter,” said Greg McGillis, superintendent of water and wastewater for the city of Little Falls.

The organic matter is plant matter generated from the corn at the ethanol plant.

“There’s no domestic waste (human waste) in this bacteria,” said McGillis. “This particular bacteria is not harmful to human beings,” he said.

 Pictured is some of the rust on the tanks. That rust was sandblasted away, primed and painted and areas where the metal was wearing out were replaced with steel.

Pictured is some of the rust on the tanks. That rust was sandblasted away, primed and painted and areas where the metal was wearing out were replaced with steel.

As the used water from the ethanol plant is pushed through to a lift station before making its way to the pretreatment facility, samples are taken every so many gallons, 24 hours a day, seven days a week, said Little Falls Public Works Director Jerry Lochner.

The pretreatment facility is efficient, said Lochner. The samples as they come into the facility test at 1,200 – 1,500 milligrams of biological oxygen demand (BOD). “If it’s really strong, it takes a lot of oxygen to break it down,” he said.

The samples, as the water comes out, test at about 50 milligrams of BOD.

Any sludge left after the pretreatment is sold by the ethanol plant to producers for use in livestock feed.

The water goes back to the city. After pretreatment, the water travels four miles to Little Falls’ main wastewater plant, where it is again purified and discharged into the Mississippi River. About 1.4 million gallons of water from the entire city goes through Little Falls’ main wastewater treatment facility.

Lochner said pretreating the water so close to the ethanol plant before sending it to the main wastewater treatment facility, reduces any odor from the plant.

The refurbishing project included sandblasting, priming and painting the interior of the tanks, replacing worn metal areas with steel and replacing all 1,600 diffusers.

Rainbow Inc. did the sandblasting, priming and painting at a final cost of about $68,500, Lochner said. The company finished the work Sept. 18 and added some heat so the curing process was cut down to just five days so the Central Minnesota Ethanol Plant could go back into production soon after.

Four-inch pipe was replaced that goes from the lift station into the building in the equalization tank, estimated at about $10,399.

County Line Welding cut out pieces of metal on the tank that were weak and welded in new metal. Several areas were found beyond what was originally targeted for patching, for a final bill of about $58,190.

The diffusers cost about $16,810, with $5,551 for installation of the diffusers and also the piping by Central Mechanical.

The money for the refurbishing had been saved in a capital improvement fund over the years, taken from money paid by the ethanol plant on its water and sewer bill, Lochner said.

The $1 million to build the original facility in 1997, was financed through the city, with the ethanol plant repaying the city the full amount with interest, Lochner said.

The work completed will keep the pretreatment facility running for another 20 years, he said.

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