Consultant's Report - Minnesota State Legislature
Consultant's Report - Minnesota State Legislature Consultant's Report - Minnesota State Legislature
Cavitation MINNESOTA DEPARTMENT OF NATURAL RESOURCES Feasibility Study to Limit the Spread of Zebra Mussels from Ossawinnamakee Lake Cavitation is a form of acoustic energy that initiates the formation and collapse ofmicrobubbles. The bubble formation occurs in the region of decreased density and pressure in an intense ultrasonic wave or high velocity turbulent water flow (Donskoy and Ludyanskiy 1995). At frequencies between 10 and 380 kHz, this type ofenergy has demonstrated mortalities ofveliger, juvenile, and adult zebra mussels (Nalepa and Schloesser 1993). Exposure times are ranges of seconds for veligers, minutes for juveniles, and hours for adults. Sound Treatment Low frequency sound energy has demonstrated prevention of settlement by translocating zebra mussels and could be a valid option to reduce the spread of zebra mussels. Sound treatment utilizes water-borne acoustic energy in the fonn of sound waves (20 Hz to 20 kHz) or ultrasound waves (above 20 kHz) to disrupt the settlement of zebra mussels (Donskoy and Ludyanskiy 1995). This type of acoustic energy is effective against veligers at frequencies below 200 Hz by causing them to become stressed and immobilized, resulting in detachment and subsequent sinking in the water column. At frequencies between 39 and 41 kHz, ultrasound acoustic energy can fragment veligers within a few seconds and can also kill adults within 19 to 24 hours. Two reports prepared for the Empire State Electric Energy Research Corporation (ESEERCO) document that frequency of 20 kHz or 42 kHz fragment or dissolve veligers in under 30 seconds (Sonalysts and Aquatic Sciences 1991, Sonalysts 1993). Vibration Vibration refers to the use of solid-borne acoustic energy in mechanical structures. This type of treatment requires that the zebra mussels be settled on a structure that can be subjected to vibration, such as pipes or water intakes. Vibrational energy is effective in killing zebra mussel veligers and juveniles at just below 200 Hz and between approximately 10 and 100 kHz (Nalepa and Schloesser 1993). Long-term effects of vibration may include structural deterioration of infrastructure (e.g., bridges, water intakes, etc.). Chemical Treatments Zebra mussel control technologies are sometimes categorized as chemical or non-chemical in the literature. They are commonly categorized in this fashion due to the environmental or toxic impacts that are a factor with chemical additions, but not with other technologies. For this reason, chemical treatments are very feasible for public facilities that can control the amount of chemical discharge, but they remain less practical for open water systems. If there is a concern of environmental impacts or harm to aquatic life, non-chemical treatments are sometimes targeted. Although many researchers have developed non-chemical strategies for control of zebra mussels, chemical alternatives remain the most common treatment due to their proven effectiveness. There are two main categories of chemical treatments: oxidants and nonoxidants. Oxidizing agents are very effective in: controlling zebra mussel populations; however, many of them also V-4 Review ofPotential Control Methods
MINNESOTA DEPARTMENT OF NATURAL RESOURCES Feasibility Study to Limit the Spread ofZebra Mussels from Ossawinnamakee Lake target other aquatic species. Nonoxidizing agents are less harmful to aquatic species such as fish, but some of them are velY toxic to native mussel species. Due to the high toxicity of chemical additions in general, it is important to survey all chemicals to determine which one will be the most effective and least harmful for each particular water system. Table B-1 in Appendix B lists variations of the chemicals discussed in this section and their potential environmental impacts. In addition, various Material Safety Data Sheets (MSDS) have been included in Appendix B. All chemical treatment options require site considerations for constructability, periodic maintenance access and supply/chemical storage. The issue of chemical storage is dependent on the frequency oftreatments, which can range from continuous dosing to one dosing per year. If the chemicals are administered through a pumping station, electrical service will also required. Furthermore, since these treatment options involve introduction of chemicals into raw water, a discharge permit may be required. Oxidants Chlorine, bromine, hydrogen peroxide, ozone, and potassium permanganate are oxidants that facilitate zebra mussel mortality when administered properly (i.e., doses and contact times). These oxidizing agents are efficient; however, some of them target organisms other than zebra mussels. In addition, adult zebra mussels can detect the presence of oxidants and subsequently close their valves. Since the mussels are capable of remaining closed for up to two weeks, longer and more frequent treatment times may be necessary to induce mortality ofadults. Chlorine/Bromine Chlorination is the most common method of treatment for zebra mussel infestation in public facilities, but it is not commonly used in treatment of open waters. This is partially due to high environmental impacts (i.e., generation of trihalomethanes), but mainly due to high toxicity toward other aquatic species. As a rule, dechlorination is required to neutralize any residual chlorine that may come into contact with aquatic life. Dechlorination is typically performed with sodium bisulfite and administered at concentrations of 1.8 to 2.0 mg/L (Sprecher and Getsinger 2000). Chlorine variations include hypochlorites, sodium chlorite, chlorine dioxide, and chloramines. Direct chlorination via hypochlorite, sodium chlorite or chlorine gas targets adult zebra mussels at a concentration of 2.0 mg/L and results in a 90% mortality rate after several weeks. Periodic or continuous treatment is usually needed to eliminate adult mussels, although less frequent treatment will be effective against veligers. A lower concentration of 0.5 mg/L is effective toward veligers and results in 100% mortality after two hours (Sprecher and Getsinger 2000). As a reference, the maximum effluent concentration for discharge of chlorine is typically 0.2 mg/L and is only allowed for two hours per day. If this concentration of chlorine were utilized for zebra mussel control, low efficacy would result. V-5 Review ofPotential Control Methods
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MINNESOTA DEPARTMENT OF NATURAL RESOURCES<br />
Feasibility Study to Limit the Spread ofZebra Mussels from Ossawinnamakee Lake<br />
target other aquatic species. Nonoxidizing agents are less harmful to aquatic species such as<br />
fish, but some of them are velY toxic to native mussel species. Due to the high toxicity of<br />
chemical additions in general, it is important to survey all chemicals to determine which one will<br />
be the most effective and least harmful for each particular water system. Table B-1 in<br />
Appendix B lists variations of the chemicals discussed in this section and their potential<br />
environmental impacts. In addition, various Material Safety Data Sheets (MSDS) have been<br />
included in Appendix B.<br />
All chemical treatment options require site considerations for constructability, periodic<br />
maintenance access and supply/chemical storage. The issue of chemical storage is dependent on<br />
the frequency oftreatments, which can range from continuous dosing to one dosing per year. If<br />
the chemicals are administered through a pumping station, electrical service will also required.<br />
Furthermore, since these treatment options involve introduction of chemicals into raw water, a<br />
discharge permit may be required.<br />
Oxidants<br />
Chlorine, bromine, hydrogen peroxide, ozone, and potassium permanganate are oxidants that<br />
facilitate zebra mussel mortality when administered properly (i.e., doses and contact times).<br />
These oxidizing agents are efficient; however, some of them target organisms other than zebra<br />
mussels. In addition, adult zebra mussels can detect the presence of oxidants and subsequently<br />
close their valves. Since the mussels are capable of remaining closed for up to two weeks,<br />
longer and more frequent treatment times may be necessary to induce mortality ofadults.<br />
Chlorine/Bromine<br />
Chlorination is the most common method of treatment for zebra mussel infestation in public<br />
facilities, but it is not commonly used in treatment of open waters. This is partially due to high<br />
environmental impacts (i.e., generation of trihalomethanes), but mainly due to high toxicity<br />
toward other aquatic species. As a rule, dechlorination is required to neutralize any residual<br />
chlorine that may come into contact with aquatic life. Dechlorination is typically performed with<br />
sodium bisulfite and administered at concentrations of 1.8 to 2.0 mg/L (Sprecher and Getsinger<br />
2000).<br />
Chlorine variations include hypochlorites, sodium chlorite, chlorine dioxide, and chloramines.<br />
Direct chlorination via hypochlorite, sodium chlorite or chlorine gas targets adult zebra mussels<br />
at a concentration of 2.0 mg/L and results in a 90% mortality rate after several weeks. Periodic<br />
or continuous treatment is usually needed to eliminate adult mussels, although less frequent<br />
treatment will be effective against veligers. A lower concentration of 0.5 mg/L is effective<br />
toward veligers and results in 100% mortality after two hours (Sprecher and Getsinger 2000). As<br />
a reference, the maximum effluent concentration for discharge of chlorine is typically 0.2 mg/L<br />
and is only allowed for two hours per day. If this concentration of chlorine were utilized for<br />
zebra mussel control, low efficacy would result.<br />
V-5<br />
Review ofPotential Control Methods
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