This section was developed using information and original text from the Zebra Mussel (Dreissena polymorpha) Control Handbook for Facility Operators.
Intermittent Treatment
Intermittent chemical use is designed to prevent initial zebra mussel infestation at facilities that cannot tolerate macrofouling. Dosing at frequent intervals (e.g., 6, 12, 24 hr) destroys post-veligers that have settled since the previous treatment. Post-veligers are more susceptible to oxidizing chemicals than are adults; thus, the concentration of the chemical and exposure times would be considerably less than if adults were the target. Because post-veligers with shells about 250 mm long can easily pass through the system, disposal and under-deposit corrosion would be eliminated.
Semicontinuous Treatment
Semicontinuous treatment is a preventative control method developed by Ontario Hydro. Because zebra mussels will stop filtering and close their shells when exposed to chlorine, the utility postulated that frequent on-off cycling of chlorine can be more effective than continuous treatment. Treatment schedules can be adjusted to 15 min on and 15 to 45 min off. Chlorination treatments consisting of 15 min on and 15 or 30 min off at the 0.5-mg/L level have been as effective as continuous treatment (Claudi and Mackie 1994). Semicontinuous treatment is ideal for facilities where several discrete systems need to be treated and results in less chemical usage than continuous chlorination.
Continuous Treatment
Continuous chemical treatment is designed for facilities that cannot tolerate any level of macrofouling. Low chemical concentrations, applied continuously, prevent any post-veliger settlement and are stressful enough to either kill adult mussels or cause them to detach and move out of the system. Continuous treatment should be carried out for the entire zebra mussel breeding season.
For a full examination of the variety of chemical control agents, see Zebra Mussel Chemical Control Guide.
Management and Control Contents