Pumps Power Lake Oxygenation in Italy
February 1, 2009
A bumper crop of fish in Italy’s Lake Varese seemed a miracle when it occurred a few years ago. But in recent years, the miracle has been that the dying lake has come back to life. The rebirth is the result of a concentrated plan of environmental management that is powered by large submersible pumps from ITT Flygt unit.
”Lago di Varese, or Lake Varese as it is 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, situated between Milan and the Swiss border. “We especially were known for perch.” In fact, says Giorgetti, fishermen used to catch as much as 25 tons of perch a year. Lake Varese is a small, pleasant lake named after the provincial capital. Its maximum depth is only 80 feet, and its total surface is just 9 square miles. When the local economy was primarily agricultural, the lake was the focal point of a respectable fishing industry, and, in the 1950s, some 32 commercial fishermen fished its waters.
Industrialization = PollutionAfter World War II, northern Italy industrialized quickly, resulting in increases in both population and pollution. “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, a company that addresses environmental issues. “The concentrated populations around these lakes resulted in a build-up of industrial and household waste.” Out of ignorance, greed or negligence, businesses dumped pollutants into Lake Varese. Households and local communities did the same, including dumping municipal waste and phosphorus from detergent use (this was before detergent makers removed such chemicals from their products).
By the 1960s, scientists began calling attention to the deterioration of the lake’s water. But it took the “miraculous fish” to sway public opinion. Fishermen caught 60 tons to 70 tons of fish per season, more than doubling their catch of previous years, due to the 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 reduced by 90 percent. Other species, including the alborella (important for the lake’s food chain), vanished permanently. In 1964, a consortium was created to monitor and protect Lake Varese. The consortium’s 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 were not completed until 1986 and cost millions of dollars. The main project was a sewage system to serve the inhabitants of the lake zone and treat the wastewater.
Today, more than 95 percent 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 (excessive nutritive substances, resulting in algae proliferation and oxygen depletion) and fish die-outs. When environmentalists dumped a huge quantity of bad-smelling algae in a central fountain in the city of Varese to dramatize the issue, citizens began pressing local authorities to move more aggressively to save the lake. The water treatment plant, the 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.
Massimo Ferrario, president of the province of Varese, asked the European Joint Research Institute to study the problem. The institute found that during the summer months, there was little oxygen at the lake’s surface, and none at all after about 15 feet. The concentrations of nitrogen and phosphorus were at least four times to five times higher than those found in clean water.
Water out, Oxygen inEventually, a multipart program for boosting the lake’s recovery was approved. The plan: 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. Because it was determined that the water in the lowest part of the lake (where the maximum depth is only 80 feet) was dense with phosphorus, nitrogen and algae, the project planners decided to remove it physically. That water now is raised and pumped by three ITT Flygt CT 3300 LT pumps to the nearby treatment plant.
Three water-pumping facilities have been constructed 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 primarily are used for pumping sewage, wastewater and storm water in municipal stations. Other application areas for this broad assortment of pumps include raw-water handling, agriculture, aquaculture, irrigation and industry. The pumps in this series have capacities ranging from 25 gallons to 2,500 gallons per second.
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 Sogeiva’s first year of operation, 4.2 tons of phosphorus and 27.5 tons of nitrogen were removed from the lake, 495 tons of oxygen were introduced, and 30 million cubic feet 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 is a small and very localized price to pay for the lake’s rebirth.
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 is the youngest commercial fisherman on the lake, and he is 65. He hopes that when the fish return en masse, younger fishermen will follow.