Fish thrive in former sewage tanks

The Fish Site
by The Fish Site
9 July 2007, at 1:00am

US - The sight of fish swimming in old sewage tanks might be disconcerting to some.

About 16,000 paddlefish live in one of the concrete tanks no longer in use by the Frankfort Sewer Department. They are being raised by Kentucky State University professor Steve Mims. The fish feed on daphnia, a crustacean that grows in tanks the plant uses for settling sewage sludge.

But one researcher hopes the paddlefish growing at Frankfort's wastewater treatment plant might one day lead to another source of food for consumers and income for limited resource farmers.

It's all a part of a combined effort from public and private entities " including Kentucky State University " to research a groundbreaking form of aquaculture using old and unused resources at the plant to grow paddlefish.

And it's working.

The process begins when tiny fingerling paddlefish are placed in large, old concrete tanks called digesters. The 300,000 gallon-digesters are no longer used to treat wastewater at the plant. Inside the tanks, the tiny paddlefish live in water disinfected with ozone.

For the first 30 days of the paddlefish's stay at the plant, they feed on daphnia, a food source that occurs at the plant during the treatment process of the sewage, said KSU professor Steven Mims.

As sludge settles to the bottom of a clarifying tank, daphnia is formed. Both Mims and Frankfort Sewer Director Bill Scalf said they don't know how or why the daphnia occur there.

A tiny crustacean that feeds on bacteria, daphnia agitates the sewage sludge, sometimes keeping part of it from settling, Scalf said.

But the treatment plant's problem has been turned into free food for the developing paddlefish, as researchers harvest the daphnia from the clarifying tank and transport it to the tiny paddlefish in the digesters, where for a month the fish feast on the food.

Harvesting the daphnia from the clarifying tanks has also made it easier for treatment plant employees to keep the wastewater clean, Mims said.

Source: The State Journal