Zebra and Quagga Mussels: Evaluation of Ultraviolet (UV) Light Treatment To Minimize Impacts of Larval Settlement in Facilities
Project ID: 2392
Principal Investigator: Fred Nibling
Research Topic: Invasive Species
Priority Area Assignments: 2010 (Zebra and Quagga Mussels), 2011 (Zebra and Quagga Mussels)
Funded Fiscal Years: 2010
Planktonic larvae of quagga and zebra mussels (veligers) may enter into hydropower facilities through water intakes, attach, and grow to maturity within the structure. This can lead to restriction or in severe cases blockage of flow and loss of function (e.g., cooling water) with serious consequences to piping system components.
* Will UV energy function as a suitable add-on device that will prevent settlement and colonization by mussel larvae in the facilities with minimal flow restriction?
* Will mussel larvae be killed by the UV radiation or merely irritated to the point that they choose not to settle?
* What are the impacts of such equipment to the routine operations of the hydropower plant?
* What is the power consumption and durability of such devices?
Based on the initial tests, can recommendations be made for more widespread operational application or for an improved UV system?
Need and Benefit
Zebra and quagga mussels are invasive, freshwater, bivalve mollusks that firmly attach to solid underwater structures and other surfaces. Originally from Eurasia, these mussels were first introduced in the Great Lakes in the mid-1980s and since then have spread to the Western United States. Adult quagga mussels were discovered in Lakes Mead and Mohave in Nevada and Lake Havasu in California/Arizona on the Colorado River in early 2007. Since then, populations have exploded and are now impacting Hoover Dam, Nevada, and Davis and Parker Dams. Arizona and Nevada. In early 2008, larval zebra mussels were confirmed to be present in Pueblo Reservoir in Colorado, and adult zebra mussels were found in San Justo Reservoir in California; which has since become heavily infested.
More recently, both zebra and quagga larvae have been detected in several other Reclamation reservoirs in Colorado, most notably those of the Colorado-Big Thompson project. In addition to California, Nevada, and Colorado, mussels are present in the Reclamation states of Arizona, Kansas, Oklahoma, Texas, South Dakota, Nebraska, and Utah. Annually, a single female mussel is capable of producing hundreds of thousands of eggs. This leads to the production of microscopic larvae (veligers) that are transported freely in the water column. Once they reach their settling stage, they attach to hard surfaces and continue to grow.
Mussel infestations are a growing concern among water management facilities throughout the Western United States. For water resources infrastructure, flow restriction and blockage are the foremost concern because mussel infestations reduce pumping and conveyance capacities and threaten water delivery and hydropower reliability. Trashracks at Hoover and Parker Dams are becoming heavily colonized, nearing 50 percent closure. Cooling systems at all three lower Colorado River hydropower dams are becoming increasingly challenged, requiring more frequent shutdowns for unscheduled maintenance and cleaning. Other impacts to facilities include enhanced corrosion of poorly protected metallic surfaces, damage to coatings, and abrasion to precision equipment surfaces. Zebra and quagga mussels can clog intakes, trashracks, strainers, pipes, fire control systems, cooling water systems, and fish screens, resulting in significant costs to protect water and hydropower systems.
While conventional chemical treatment (e.g., chlorine) has been shown to be somewhat effective in the Eastern United States, it is costly, often requires discharge permitting, and can result in environmentally adverse byproducts and other impacts. Research of _Pseudomonas fluorescens_ for mussel control offers environmentally friendly, innovative treatment methods without these drawbacks.
In the last few years, the cooling water supply lines at Hoover Dam have been exposed to colonization by quagga mussels. This has resulted in lower water pressure and restrictions in the flow at the central section station air compressor heat exchangers and on some generating units. This is likely due to mussel colonization and resulting plugging from sloughing of shells. A recent inspection of the existing high pressure and cooling water supply lines verified that Hoover Dam has excessive exposure to quagga mussel infestation and that adding mussel control barriers are needed to prevent further loss of cooling capacity. This buildup of mussels has resulted in a number of high temperature warnings and more frequent shutdowns for unscheduled maintenance.
Successful development of the UV system would provide a means of preventing or limiting mussel colonization in sensitive areas without flow obstructing devices. The primary advantage of this treatment method is that it would eliminate the need for discharge permitting, and it represents an environmentally safe alternative to conventional alternatives such as oxidants.
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