Dairyland Power Cooperative Return to regular view

Original Story URL:
http://www.dairynet.com/environment/zmussels.php


Zebra Mussel Control

picture of zebra musselsSince zebra mussels were first found in the Mississippi River on Sept. 12, 1991, their population has been exploding. Dairyland staff partnered with the Electric Power Research Institute (EPRI) to develop a report on controlling zebra mussel infestation.

Zebra mussels are freshwater mollusks that can cause serious problems, such as clogging the intake systems at Dairyland’s power plants along the Mississippi River. Research and control of this exotic invader has been costly at Dairyland. Research conducted at Dairyland’s John P. Madgett Station found steam treatment to be an effective control method which could save Dairyland and the industry millions of dollars.

A hydrovac system from Brennan, Maine is used at both the Genoa and Alma sites. The system is essentially a high-pressure vacuum cleaner.

At the Alma site, zebra mussel control is also aided by a biannual thermal backflush. Heated water is stored, then backflushed through the service water systems.

Zebra mussels can grow from 30 mussels per square meter to a whopping 90,000 mussels per square meter in about three months.

The tiny clam-like mollusks have a hard brown and yellow banded shell. They excrete a glue-like mucus that, along with bundles of strong byssus thread that extend from the opening of their shell, allows them to stick to hard surfaces. Each individual mussel has 200 threads per bundle.

One zebra mussel can produce as many as a million eggs per year resulting in as many as 30,000 new mussels. The eggs become free swimming larvae, called veligers, that grow shells and settle onto any firm surface.

When there isn’t anything else available, they collect on the lake or river floor and attach to each other, forming clumps and layers that are inches thick and are seriously threatening to power plant intake systems. These clumps can block the water flow in the condenser tube, which creates back pressure on the turbines. They can also choke down the available diameter of pipes needed to transport water and block strainers and screens to cause acute clogging.