Pumps power lake oxygenation in Italy and restore fishing industry
Liquid oxygen is vaporized, mixed in water by ejectors connected to 15 Flygt
CS 3152 MT pumps and then pumped into the lake.
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 Industries’ 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 were
especially 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 25 metres, and
its total surface is just 14.5 square kilometres.
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.
After 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, 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 catalyze public opinion.
Fishermen caught 60 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 billions of lire. The main project
was a sewage system to serve the
inhabitants of the lake zone and treat
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.
After 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.
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 that during the summer
months there was little oxygen at the
lake’s surface, and none at all after
about five metres. The concentrations
of nitrogen and phosphorus were at
least four to five times higher than
those found in “clean” water.
Two years later, in 1996, a multipart
program for boosting the lake’s recovery
was approved. It comprised:
Physically removing the nutrientrich
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
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 25
metres) was dense with phosphorus,
nitrogen and algae, the project planners
decided to remove it physically.
That water is now raised and pumped
by three 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 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.
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 tons of phosphorus and
27.5 tons 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 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 over 65. He hopes that
when the fish return en masse,
younger fishermen will follow.
