D.C.'s National Aquarium Fills Tanks From City Tap
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By Juliet Eilperin
Washington Post Staff Writer
Monday, August 18, 2008

". . . like a fish to water."

It's a cliche that describes something effortless, but if you're running an aquarium, there is nothing effortless about filling your tanks with water that won't kill your horn sharks, loggerhead turtles and sea horses.

The myriad fish, invertebrates and plants thriving in the 66 tanks of the District's newly renovated National Aquarium swim in D.C. tap water -- albeit tap water that has gone through an elaborate filtration and treatment process to make it habitable.

"D.C. water is abominable. It cannot sustain life," Andy Dehart, who directs biological programs at the aquarium, declared at a recent briefing.

The aquarium's executive director, Bob Ramin, winced and jumped in to offer a reassuring plug for the local water: "But it's safe to drink!" Dehart was having none of it, though.

"Maybe," he conceded, but he added: "It's not safe for fish, especially for invertebrates."

The aquarium has put in place a complex water-treatment system as part of a recent four-year, nearly $1.6 million upgrade funded by the National Oceanic and Atmospheric Administration, which highlights scientists' increasingly sophisticated understanding of what marine creatures need to survive in captivity. In the past, many aquariums focused mainly on removing harmful particulates such as uneaten food and fish waste. Today, they apply a range of techniques to make the water as close as possible to the creatures' native environments.

"Old-school life support focused primarily on mechanical filtration," said Andy Aiken, resident life support engineer at Baltimore's National Aquarium, who consulted on the District's aquarium. "Over time, [researchers] realized that's not enough to maintain the environment for fishes, invertebrates and to some extent, marine mammals."

After decades of residing largely unnoticed in the basement of the Commerce Department, the tiny National Aquarium -- which, founded in 1873, is the country's oldest -- is seeking a higher profile. But, to compete with more recent and far larger aquariums in Baltimore and elsewhere, the operation needed to modernize. The city's water did not make the job any easier.

To make it safe for people, the tap water -- which is treated with the disinfectant chloramine year-round to kill bacteria and with chlorine in the summer -- goes through multiple treatments to eliminate these chemicals and make it safe for fish. The aquarium has two eight-foot-high vessels filled with activated carbon that converts the chloramine into a form of ammonia to make it less toxic. Then the water passes through a separate, equally large cylinder containing the mineral zeolite, which neutralizes the ammonia through an ion exchange. Then the water passes through a smaller vessel that breaks down the nitrite and nitrate compounds formed through this process.

Aiken, who consults with aquariums from the Bahamas to Dubai, helped the National Aquarium install two other levels of filters, fractionators and biofilters. Fractionators, which are also known as protein skimmers, remove dissolved organic waste from vegetation and animals by pumping air bubbles through the tank's water column. The bubbles attract long chains of organic molecules that form a foam at the top, which is skimmed off. The biofilter helps recalibrate the balance between oxygen and carbon dioxide by passing the water over a flat plastic surface that allows the two gases to return to their natural equilibrium.

"If you don't have all these pieces of the puzzle, there will be some issue with the environment in which these animals are swimming," Aiken said. Before the renovation, he added, the aquarium's life-support system "was sort of a hodgepodge of this, that and the other thing."

Most of the National Aquarium's tanks are home to saltwater creatures, so officials take the additional step of increasing the salinity of the treated tap water. They rely on a product named "Instant Ocean," a synthetic sea salt.

Aquariums near the shore have an easier time of it. The Monterey Bay Aquarium in California has a pipeline into the bay that provides its exhibits with seawater 24 hours a day at a rate of 2,000 gallons per minute, or 2.9 million gallons a day.

In some instances, said Monterey's husbandry curator, Paul Clarkson, officials put the seawater "straight on in" to exhibits such as its kelp forest, which features local vegetation. The water is nutrient-rich with larvae and invertebrates. "You'll see lots of sea life which we didn't put there," Clarkson said.

But visitors expect water that is clear enough for them to see the marine life, he added, so officials pump in filtered water in the daytime and unfiltered water at night at a rate that turns over the kelp forest's 330,000-gallon tank's volume least once every 90 minutes.

"If you look at the kelp forest exhibit during the day, it looks really clear and fabulous," Clarkson said. "If you come through at 2 in the morning, that raw water is coming in without any filtration, so it's a lot murkier."

Because the Monterey Aquarium returns its seawater to the Bay, it takes the additional step of ultraviolet sterilization to ensure it does not introduce invasive species into the bay. Without treatment, water from the exotic jellyfish exhibit, for example, could contaminate the bay and harm native species.

In a few instances, Monterey Bay officials use treated tap water for freshwater tanks, including a trout stream and an otter exhibit. They rely on the same carbon filtration system as the National Aquarium, along with ultraviolet sanitation, mechanical filters and a bacteria-containing sand filter to break down ammonia-based waste.

By the time this water goes down the drain, Clarkson said, "It's essentially pristine water going into the sewer system. We're accountable for every single drop of water that leaves the building."