General

New, high-tech filtration system helps protect small Missouri River fish 

OPPD is adding a new, high-tech tool to help protect fish that swim too close to its Nebraska City Station (NCS) generating plant. 

NCS Unit 1 draws water from the Missouri River to help cool the super-heated steam that passes through turbines to generate power for eastern Nebraska. The cooling water then circulates back into the river and continues its journey downstream. 

The plant already has filters to keep out most fish, but some are too small or weak to escape the intake current. To better protect those fish and comply with the Federal Clean Water Act, OPPD needed an upgraded filtration system with fish protection technology. 

Once fully installed, the new “Passavant-Geiger MultiDisc with Fish Return Systems” machinery will capture those fish and return them safely to the river. 

How it works 

The new system operates as a sort of oval-shaped Ferris wheel. A roller chain on sprockets pulls a rotating line of buckets through the water, similar to a bike chain turning a gear. 

The buckets, with a mesh-screen backing, scoop up fish as they enter the water-intake area, then carry them upward. 

As the fish reach the top of the system, the buckets tilt inward. Each fish slips out of the bucket and into a water slide that whisks them back out to the river and clear of the plant. A video to illustrate the system is available here. 

An OPPD team of contractors and engineers is working to install the new fish-friendly system and ensure that every piece integrates smoothly with NCS’s existing infrastructure. The work is tentatively set for completion by this summer. 

Engineers focused on the smallest of details for the project, from the depth of the water that holds the fish to the incline angle of the trough that carries them back out to the river. An electric motor drives the pulley chain. The plastic buckets with a protective coating and stainless-steel trough are built to resist corrosion from the constant water exposure. 

OPPD’s North Omaha Station has added a similar system, but a slightly different model. 

“There are specific mechanisms to catch the fish and wash them into the trough to return them back to the river,” said Daniel Cano, an OPPD design engineer who is overseeing the project at North Omaha Station. “We’re using the best available technology to achieve that goal.” 

Why it’s needed

Federal law requires cooling water users, such as OPPD, to protect fish from cooling water intakes. OPPD uses Missouri River water to cool the steam that spins the turbine in each generating unit. Unlike the cooling water from the river, the steam that powers each unit operates in a closed loop and needs to be converted back into liquid water, then recycled within the plant so it can continue spinning the generators. 

The plant’s cooling system pumps about 340,000 gallons per minute from the river. That’s enough to fill an Olympic-sized swimming pool once every two minutes. 

All that water travels through protective screens to keep fish, plants and various river gunk out of the system. 

OPPD employees will monitor the machinery closely to ensure it protects fish as designed. A third-party engineering firm will test the new equipment over several months to ensure it’s operating as designed and complying with federal requirements.