Zebra and Quagga Mussels: Control of __Dreissena__ BioFouling Using Carbon Dioxide
Can carbon dioxide (CO[v2]) be used to control _Dreissena_ species (zebra and quagga mussels) in confined water?
Need and Benefit
Reclamation reservoirs in four of the five Reclamation regions (Great Plains [GP], Upper Colorado [UC], Lower Colorado [LC], and Mid-Pacific [MP]) are currently infested. Reclamation has a need for an effective, economical, and nonpolluting management control programs that will allow managers to minimize or eliminate the threats that these mussels pose to the operation and maintenance of Reclamation water systems. Mitigation of the threat the zebra and quagga mussels impose currently can be accomplished primarily by one of two means: chemical treatment and mechanical/nonchemical cleaning.
Due to a lack of options, chlorination is considered to be the most effective and popular method of chemical control. Like most chemical controls, it can be used as either in a proactive or reactive control strategy. However, chlorination is a broad-spectrum chemical biocide and a powerful oxidant. Chlorination is also becoming increasingly more regulated and may eventually be banned by individual states and/or the Federal government.
Salt treatment (i.e., potassium chloride [KCl]) has been used successfully to eradicate zebra mussels from a water body. However, the cost of the most common source of this chemical, muriate of potash, has increased more than five-fold within the past one year (over $1,000/metric ton). To be effective, a large amount of potash would be necessary to maintain the optimum lethal concentration level (typically 100 parts per million [ppm]) in a body of water for a sustained period of time.
Among mechanical/nonchemical treatment, filters (sand, mechanical) are probably the most popular proactive strategies for protecting the entire water delivery system by installing the filters at the system intake. Other mechanical/nonchemical possibilities include ultraviolet (UV) exposure, acoustics, antifouling coatings, and thermal treatment. On large water systems, the retrofit required is expensive relative to carbon dioxide, may be difficult to implement, may not be 100 percent effective, and for some mechanical/nonchemical treatments, can cause an unacceptable drop in flow or pressure in the system.
Extreme Hypoxia (lack of oxygen) can be a very effective method of eradication. For example, no zebra mussels could be found below approximately 30 feet at San Justo Reservoir, California due to annual reservoir stratification, despite at least several years of infestation. A simple lowering and raising of the reservoir level should be sufficient to eradicate the entire local population of zebra mussels. However, hypoxia may not be feasible for some confined water (conduits) where water is continually mixed and flowing.
CO[v2] is a natural chemical that does not require a separate or specialized production (e.g., fermentation), is already produced in large quantities, is recycled from initial combustion waste streams for good environmental stewardship, has an indefinite shelf life, is nonflammable, is easy to handle and store, does not require electrical or mechanical power to deliver, and can be distributed easily and evenly in water (including hard-to-reach confined water). Through the carbonic acid/bicarbonate buffer, the change in pH of the water is limited. Addition of CO[v2] also reduces the bioavailibility of calcium in the water, thereby inhibiting shell growth. Only species that have taken up residence in the confined water (i.e. Dreissinids) would be exposed long enough to reach mortality levels. Once the water is freely exposed to the air at the outlet, purged, or the CO[v2] is stripped and reused, equilibrium is quickly re-established and partial pressure of carbon dioxide (P[vCO2]) goes back to ambient pressure, so that it will not affect the downstream water ecology.
Unlike other inventions to control _Dreissena_ species, the patent for the use of CO[v2] as a control agent for invasive species (No. 6, 821, 442) is owned by the United States of America as represented by the Secretary of the Depar
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