Effective Removal of Zebra Mussels with Amiad Screen Technology

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Courtesy of Amiad Filtration Systems Ltd.

Introduction

The zebra mussel, native to the Black and Caspian Seas, has spread in the past few decades to waterways throughout the world mostly via ballast water. Zebra mussels, when non-indigenous to the environment, pose a serious threat to intakes of facilities that rely on fresh and brackish surface water. The mussel colonies obstruct the flow of water through the pipelines eventually causing the complete blockage of the piping system. This could be extremely dangerous if it were to happen at, for example, a nuclear power plant.

The need to eradicate zebra mussels is a growing concern, due mostly to the heavy costs incurred by facilities that rely on water drawn from lakes and rivers. The AMIAD solution helps these facilities cut expenses by ensuring the uninterrupted supply of mussel-free water. Zebra mussels are a serious threat to surface water resources due to their ability to attach to underwater objects and surfaces.

What are Zebra Mussels?

Zebra mussels are bi-valve mollusks and although known for their black-and-white stripes, other colors and patterns are common. The high reproduction rate combined with the lack of natural enemies cause the rapid infestation of these mussels in foreign ecosystems. The mussels flourish in oxygenated plankton-rich water and can even survive in dark surroundings of water lines. Fertilized eggs develop into free-swimming larvae known as veligers. The veligers remain suspended in water until the juvenile stage at which time they secrete byssal threads - a sticky substance that allows the mussels to adhere to hard surfaces such as water lines. Groups of juvenile mussels colonize the inner surface of pipelines producing a hard substrate. As the mussels develop shells, they become the substrate for new colonies. Able to withstand high water flows, the growing layers of colonies decrease the diameter of the pipelines impeding the normal passage of water. In addition the high flow rates in water intake pipes provide a constant source of plankton for the filter-feeding mussels.

Why are zebra mussels a threat?

Zebra mussels are notorious for their biofouling capabilities by colonizing water supply pipes. The ability to attach themselves to any hard underwater object or surface poses a serious threat to water treatment and industrial plants. These facilities spend millions of dollars annually since they must:

- Consume more energy to maintain required water flows
- Carry out costly maintenance activities (manual cleaning of pipelines) that sometimes cause plant shutdowns
- Clean chemically treated water to allow for its safe discharge

Mussels cluster in mats on top of each other, lining the inside of pipes. When these clusters become too heavy, they slough off the pipes, lodge in intakes, and constrict water flow. They reduce the available diameter of pipes needed to transport water and block strainers and screens. The fouling and loss of intake heads, obstruction of valves, corrosion of cast iron and steel piping are common to industries as well as facilities and services that use mussel infested surface water.

Some of these include the following:

- Hydroelectric and nuclear power plants
- Water treatment works. The putrid smell of decaying mussels, and buildup of methane gasses from the decaying mussel tissue cause significant taste and odor problems in drinking water.
- Aquaculture
– Fish hatcheries/farms.

In addition to the threat of pipe blockages, contaminated fish farms face quarantine measures to prevent the spread of zebra mussels.

The types of equipment that are vulnerabe to the build up of mussel colonies include:

- Heat exchangers
- Cooling systems
- Air conditioning systems
- Condenser units
- Turbines
- Fire fighting equipment
- Small-diameter pipes
- Seals
- Valves

Farms and golf courses may also be likely targets of infestation.

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