Pumps Power Lake oxygenation in Italy

A bumper crop of fish in Lake Varese seemed a miracle a few years ago, but the Italian lake’s rebirth was a result of a concentrated environmental management plan powered by big ITT Flygt submersible pumps.

Liquid oxygen from Air Liquide is vaporized and mixed in water by ejectors connected to over a dozen CS 3152 MT pumps from ITT Flygt and then pumped into the lake.

Lago di Varese, or Lake Varese as it’s known in English, used to be considered among the most “fishable” lakes in Europe, says Natale Giorgetti, one of the few remaining fishermen of this northern Italian lake between Milan and the Swiss border. “We were especially known for perch.” In fact, he says, fishermen used to catch as much as 25 tons of perch a year.

A small, pleasant lake named after the provincial capital, its maximum depth is only 25 meters and the total surface is just 14.5 square kilometres. When the local economy was largely agricultural, the lake was the focal point of a respectable fishing industry. And, in the 1950s, some 32 commercial fishermen fished its waters.

Industrialization and pollution

After World War II, northern Italy industrialised quickly with jumps in both population and pollution as well. “Lake Varese encountered a problem endemic to all shallow pre–Alpine lakes in Italy,” observes Carlo Gabardini, president of Sogeiva S.p.A. Varese Ambiente, an environmental engineering consultant. “The concentrated populations resulted in a build–up of industrial and household waste.” Businesses dumped pollutants into Lake Varese. Households and local communities did the same, including dumping municipal waste and phosphorus from detergent use — before detergent makers removed such chemicals from their products.

By the 1960s, scientists began calling attention to deterioration of the lake’s water. But it took the “miraculous fish” to catalyse public opinion. Fishermen caught 60 to 70 tons of fish per season, more than doubling their catch of previous years, due to excess of nutrients in the water — the result of years of unchecked pollution. Soon, however, as oxygen was depleted from the water, fish began dying by the thousands. Giorgetti saw his yearly catch of perch cut by 90%. Other species, including the alborella (important for the lake’s food chain), vanished entirely. In 1964, a consortium was created to monitor and protect Lake Varese. Its first projects were to build a drain around the lake, to collect the waste pouring into it, and a water treatment plant. But these projects weren’t completed until 1986 and cost billions of lire (millions of U.S. dollars). The main project was a sewage system to serve inhabitants of the lake zone and treat the wastewater.

Today, over 95% of the local population of more than 70,000 is connected to the sewage system, and pollution in the lake has decreased significantly. Nevertheless, at the time, the situation continued to worsen, marked by pollution–induced eutrophication, algae proliferation and fish die–outs.

When environmentalists dumped bad–smelling algae in a central fountain in the city of Varese to dramatise the issue, citizens began pressing local authorities to move more aggressively to save the lake. The water treatment plant, drain and more stringent anti–pollution requirements were, in fact, helping the lake recover, but the process promised to be a long one. Meanwhile, the number of commercial fishermen dropped to seven.

In 1994, Massimo Ferrario, president of the province of Varese, asked the European Joint Research Institute in Ispra to study the problem. The institute found, during summer months, there was little oxygen at the lake’s surface and none at all after about five meters. And concentrations of nitrogen and phosphorus were at least four to five times higher than those found in “clean” water.

Pumping water out, oxygen in

Two years later, in 1996, a multipart program to boost the lake’s recovery was approved, comprising:

• Physically removing the nutrient–rich but oxygen–deprived water in the deepest part of the lake, and pumping it to the Bardello river, which would carry it to Lago Maggiore, a much larger, deeper lake nearby; and
• Pumping oxygen directly into the lake at three strategically placed locations.

The two–pronged attack on the polluted waters of Lake Varese involved ITT Flygt pumps in two different ways. Since it was determined water in the lowest part of the lake was dense with phosphorus, nitrogen and algae, project planners decided to remove it physically. That water is now raised and pumped by three ITT Flygt CT 3300 LT pumps to the nearby treatment plant.

Three water pumping facilities were built along the southern end of the lake. Here, liquid oxygen is vaporized, mixed in water by ejectors connected to 15 ITT Flygt CS 3152 MT pumps and then pumped into the lake. The choice was made to use liquid oxygen rather than ambient air because of the scarcity of oxygen in the lake. A large amount of oxygen was needed, and liquid oxygen supplies much more than air. The higher cost of liquid oxygen is more than compensated for by the rapid results it delivers.

In addition to this unusual lake oxygenation application, the pumps in ITT Flygt’s C3000 Series of large centrifugal pumps are used primarily for pumping sewage, wastewater, and stormwater in municipal stations. With capacities from 100–2,000 liters per second, other application areas for this broad assortment of highly reliable pumps include raw–water handling, agriculture, aquaculture, irrigation and industry.

Sogeiva was entrusted with running the water treatment plant and the oxygenation process. The pumping and oxygenation are done only during the warm months of the year because the heat “stratifies” the lake’s waters and facilitates the process, explains Gabardini.

In 2000, Sogeiva’s first year of operation, 4.2 tonnes of phosphorus and 27.5 tonnes of nitrogen were removed from the lake, 495 tonnes of oxygen were introduced, and 10 million cubic metres of bottom water were pumped out. The only noticeable sign of this activity, other than the physical plant itself, the discreetly–placed underground pumps and the buoys marking the areas of oxygenation, is the rotten–egg smell wafting along the lakeside just by the water treatment plant. It’s a small, very localised price to pay for the lake’s rebirth.

Conclusion

Even the fish are beginning to return. Giorgetti’s catch of perch has doubled from the bad years, and fish farms are re–introducing other species. Still, Giorgetti points out that he’s the youngest commercial fisherman on the lake, and he’s over 65. He hopes that when the fish return en masse, younger fishermen will follow.