What operational strategies can be employed to mitigate the impact of zebra mussel infestations on raw water intake structures?

Zebra mussels are invasive species that can cause significant problems for raw water intake structures by attaching to surfaces and forming dense colonies, which can reduce flow capacity and damage equipment. Several operational strategies can be employed to mitigate the impact of zebra mussel infestations: 1) Physical Removal: Regular physical removal of zebra mussels from intake structures is a common strategy. This can involve manual scraping, brushing, or high-pressure washing. The frequency of physical removal depends on the severity of the infestation. 2) Chemical Control: Chemical treatments, such as chlorination or the use of molluscicides, can be used to kill zebra mussels. However, these treatments must be carefully controlled to minimize the impact on non-target organisms and comply with environmental regulations. Chlorination is typically used at low doses to prevent mussel settlement, while molluscicides are used for more severe infestations. 3) Thermal Control: Thermal control involves raising the water temperature to levels that are lethal to zebra mussels. This can be achieved by heating the water or by shutting down the intake for a period of time during the warmest months. However, thermal control is not always feasible and can be energy-intensive. 4) Intake Design and Location: Designing intake structures to minimize zebra mussel attachment is a preventative strategy. This can involve using smooth surfaces, installing screens with small openings, and locating the intake in areas with high flow velocities. 5) Barrier Coatings: Applying barrier coatings to intake surfaces can prevent zebra mussels from attaching. These coatings can be toxic or non-toxic and may need to be reapplied periodically. 6) Velocity Control: Maintaining high water velocities in intake pipes can prevent zebra mussel settlement. Zebra mussels prefer to settle in areas with low flow velocities. 7) Monitoring: Regular monitoring of zebra mussel populations is essential for detecting infestations early and implementing control measures promptly. Monitoring can involve visual inspections, veliger sampling (sampling for zebra mussel larvae), and the use of settlement samplers. For example, a water treatment plant drawing water from a lake infested with zebra mussels might implement a combination of physical removal, low-dose chlorination during the spawning season, and regular monitoring to prevent severe infestations and maintain intake capacity.