Philadelphia Is Using Mussels as Mini Treatment Plants

Cooperative ‘blue infrastructure’ program aims to restore Philadelphia watershed

Philadelphia Is Using Mussels as Mini Treatment Plants

In conjunction with a separate hatchery that will be built and run by Partnership for the Delaware Estuary, the city of Philadelphia is investing in a freshwater mussel program that aims to improve water quality in the Delaware River Basin. (Photos Courtesy of the City of Philadelphia)

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Living organisms have always been a part of water treatment, but a first-of-its-kind facility in Philadelphia is advancing that concept from microscopic organisms to filtering water with freshwater mussels.

In 1815, Philadelphia had the distinction of building one of the nation’s first municipal water distribution plants. They are continuing that legacy of innovation with the nation’s first city-owned mussel hatchery.

The exhibition laboratory is housed in the very same Fairmount Water Works facility that made history in the early 1800s. In conjunction with a separate production-scale hatchery that will be built and run by Partnership for the Delaware Estuary, the project is an effort to improve water quality in the Delaware River Basin.

“We’ve created a freshwater mussel hatchery to reintroduce our native species, both established and threatened endangered species, back into our Delaware and Schuykill rivers, and our small tributaries,” Butler says. “That’s the gist of what we’re doing here.”

A mussel at the hatchery.
A mussel at the hatchery.

The city draws water directly from the Schuykill River and Delaware River. Once upon a time, it drew water for direct distribution, but pollution during the Industrial Revolution and beyond has led to poor water quality, and steadily increased levels of water treatment.

Hopes are that this effort will improve the city’s source water and potentially save taxpayer money on treatment costs.

“Few places that once had such mussel beds currently have any mussels at all,” says Danielle Kreeger, science director with Partnership for the Delaware Estuary. “The decline of natural mussel beds in our nation's waterways means that we have lost natural ecosystem services that helped to sustain water quality. This in turn means that we need to spend more money to mechanically filter water when used for drinking water.”

Blue infrastructure

Gray and green infrastructure improvements are common, but this program features something Butler is calling “blue infrastructure.” He defines it as “biological communities performing certain ecosystem services for you naturally.”

In this case, bringing the mussel population back up to its natural levels should revitalize the Basin’s ecosystem, spurring new aquatic vegetative growth, creating habitat for fish and eventually bringing the water itself back to its natural purity.

“We used to have huge populations, or very diverse populations, of freshwater mussels in the Basin area in Philadelphia,” Butler says.

The same pollution that tainted the water around the turn of the 20th century killed off much of the mussel population, even endangering some species native to that area.

“They’re the canaries in the coal mine: They’re great biological indicators, they’re long-lived, they’re sentinel, so it makes sense,” Butler says.

It’s not a problem specific to the city — the broader context of Philadelphia’s hatcheries is the Freshwater Mussel Recovery Program, which is implemented across the 13,000-square-mile Delaware River Basin.

“We have had a watershed-wide shellfish restoration strategy that includes oyster restoration in Delaware Bay, saltwater mussels along the tidal shorelines and freshwater mussels in rivers,” Kreeger says. “The main goal is to rebuild populations of native oyster reefs and mussel beds so that they help filter particulate pollutants, enhance fish populations, stabilize erosion, et cetera.”

While similar programs in other areas run by state or federal agencies like the Fish and Wildlife Service focus on endangered species, the city and partnership hatcheries are starting with species that are already established.

“Most existing mussel restoration projects have focused on saving imperiled species, not necessarily promoting water quality. We are also interested in stemming biodiversity losses, but the top goal is to enhance ecosystem benefits of healthy beds of mussels, such as the filtration of polluting particles,” Kreeger says.

Education and experimentation

The Fairmount hatchery serves several purposes: It is a testing ground for the larger hatchery that will be run by Partnership for the Delaware Estuary, in addition to contributing a significant number of mussels to the watershed, and it is also an educational facility.

“We have students ranging from kindergarten all the way up to 12th grade, going through the hatchery, understanding the process. We also have cooperative students from universities working on research projects here.”

A subsample of mussels is donated to local classrooms in special habitat units for students to monitor and learn about the process by eventually releasing the mussels into streams.

“It has been a huge success for outreach, and we have also been able to use the facility to address lingering research questions, as well as produce some mussel offspring,” Kreeger says.

They are hoping to average 5,000 to 15,000 new mussels annually, while the partnership hatchery will use its research and processes to introduce between 500,000 and 1 million new mussels each year.

“That’s one of the guiding tenets of this educational facility, is how to optimize the process, how to maximize the likelihood of survivability, and also look at the different ways that we can reproduce this process with minimal bottlenecks. Because it’s a very complicated process, there’s a lot of different steps to make this successful,” Butler says.

The life cycle of freshwater mussels is complex and unique: After the larvae are released from the mother clam, they latch onto the gills of fish, which then transport the larvae while they grow.

The larvae attaching to the gills of a fish.
The larvae attaching to the gills of a fish.

Each species of mussel has very distinct requirements, even down to the species of fish they will target for inoculation. Because of that, finding ways to propagate new species takes time and experimentation.

“This small educational hatchery is in its second year — the first year we propagated about 20,000 mussels,” Butler says. “This year is about determining how many different species we can propagate, so can we propagate new species in laboratory, and if yes, how many can we do? To date, we’ve propagated two different species successfully.”

In the coming weeks, they plan to test two more species, with the ultimate goal of re-establishing as many of the original native populations as possible.

The facility includes a fish hatchery to facilitate larvae growth for the mussels.
The facility includes a fish hatchery to facilitate larvae growth for the mussels.

Innovation for the future

The city’s educational hatchery was built with a $300,000 PEW grant, while the larger production hatchery has $7.9 million in funding from the state, though Kreeger says that are still seeking additional funding.

As a “miniature wastewater treatment plant,” the mussel beds filter many of the same purification targets as traditional treatment plants: they have shown reductions in TSS, microbes, BOD, nitrogen and phosphorus.

“Basically, improvement in water quality coming into the treatment facility equals lower cost at the chemical end,” Butler says. “The healthier the water quality coming into your intakes for drinking water, the less chemical treatment you need.

“These freshwater mussels can filter anywhere from 10 to 20 gallons per day, so if you think about reintroducing a hundred thousand, a million, 10 million, 100 million, into our drainages, you are essentially creating mini-wastewater treatment plants for pretreatment for your drinking water intakes.”

It will take years to see any effect on the area’s water quality, but small-scale tests have been promising. “Restoration of mussel beds should not be viewed as a magic bullet that will fix our water quality problems.” Kreeger says. “There are many important questions to be addressed. But based on what we know now, it is plausible that mussel bed restoration might be useful as a new best management practice that would augment existing practices.”


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