Alternate Control Strategy for Dreissinids Using Carbon Dioxide
Can carbon dioxide be used as an environmentally neutral molluscicide for mitigation of zebra and quagga mussel macrofouling?
Need and Benefit
Reclamation reservoirs in four of the five Reclamation regions (GP, UC, LC, and MP) are currently infested. Reclamation has a need for an effective, economical, and non-polluting management control programs that managers to minimize or eliminate the threats 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 removal.
Chlorination is considered to be the most effective and popular method of chemical control. Like most chemical controls, it can be utilized 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 increasily more regulated and may eventually be banned by individual states and/or the federal government. Salt treatment (i.e. 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 5 folds within the past few years (> $1,000/metric ton). To be effective, a large amount of potash would be necessary to maintain the optimum lethal concentration level (typically 100 ppm) in a body of water for a sustained period of time.
Among mechanical treatments, 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 possibilities include 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% effective, and for some mechanical treatment, 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. However, hypoxia may not be feasible for some confined water (conduits) where water is continually mixed and flowing.
Carbon dioxide 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, 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 carbon dioxide also reduces the bioavailability of calcium in the water, thereby inhibiting shell growth. Only species that has 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 CO2 is stripped and reused, equilibrium is quickly re-established and PCO2 goes back to ambient pressure, so that it will not affect the downstream water ecology.
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