Solar-powered circulation technology clears out blue-green algae
By Ed Sullivan
The Palmdale (California) Water District had been using up to 3,000 lbs of copper
sulphate powder per week to control algae growth in its 4,130 acre-ft lake
until it put in a SolarBee unit.
Annual onslaughts of bluegreen
algae (cyanobacteria)
blooms continue to plague
fresh water lakes and reservoirs.
In the past, copper sulphate has
been the chemical of choice for treating
blue-green algae. However, as the
algae become increasingly resistant to
copper sulphate, continuously larger
doses are required for effective control.
Furthermore, impacts on zooplankton
and other life forms have led
to increasingly stringent permitting
requirements for its use.
A non-toxic solution arrives
Due to all the problems associated
with stagnant water and chemical
treatments, the principle of forced circulation
of lakes and reservoirs has
gained increasing interest in recent
years. “If you can create sufficient circulation,
blue-green algae problems
and other unwanted water conditions
can be avoided or even corrected,” says
Joel Bleth, president of Pump
Systems, Inc. (PSI), Dickinson, North
Dakota. “Sufficient circulation will
minimize or eliminate the need for
chemical and carbon treatments
because it prevents blue-green algae
takeover.”
To provide reliable and flexible
forced circulation, PSI developed
SolarBee™, a floating self-contained
system for use in lakes and reservoirs.
Powered by solar modules, this system
features an adjustable down-hose suspended
from an anchored flotation
unit. A single unit can draw up to
10,000 (US) gallons of water per
minute and spreads it gently across the
surface for continuous aeration 24-
hours per day.
Mechanism of operation of the SolarBee system.
The system’s mixing action prevents
the takeover of blue-green
algae and promotes a good crop of
diatoms (“good algae”) and zooplankton.
Instead of constantly sinking
to the bottom and being blocked
from the sunlight, they continuously
glide up and down in the mixing currents.
At the same time, continuous
circulation prevents the blue-greens
from blocking the sunlight below the
water surface.
When used to control blue-green
algae growth, units are positioned at
problem locations, with the unit’s
down-hose suspended to just above
the thermocline. The water intake,
from the relatively warm epilimniun
layer, is pumped up the down-hose
and spread across the water surface,
providing beneficial turbulence and
aeration. The resulting circulation of
the epilimnium prevents the bluegreen
algae from staying at the top of
the layer, so that diatoms are able to
out-compete the blue-green algae.
Units may be installed throughout the
year as long as ice has not formed on
the lake or reservoir.
Case studies
At Palmdale Lake in the high desert
country of southern California, the
Palmdale Water District had been using 2,000 to 3,000 lbs. of copper sulphate
powder per week from March to
September to control algae growth in
its 4,130 acre-ft. of water.
“Besides being expensive, we wanted
to avoid using excess copper,” says
Greg Dluzak, Palmdale Water District
Production and Control Superintendent.
“So we were very pleased that
a year after installing seven of these
SolarBee circulation units we had
greatly reduced the amount of copper
that we were using.”
“We also saw considerably more
dissolved oxygen that was much more
evenly dispersed throughout the lake,”
Dluzak says. "The water temperature
was much more even, and we weren’t
getting our usual spring or fall
turnover. The lake also looks much
clearer than it did before, which makes
it much easier to see the fish, too”
Another problem that often results
from blue-green algae blooms is filter
clogging at treatment plants. At the
Palmdale plant this problem occurred
almost continuously throughout the
year. “Since installing these new circulation
units we have only experienced
two or three weeks of excessive clogging
of our filters during the algae
growing season, per year,” Dluzak
says. “We’re planning on upgrading
our units to the new V12 model with
the larger battery and solar panels,
which will operate 24 hours per day as
compared to the current units (without
batteries) that only run during daylight
hours, so we’re hoping that the filter
clogging will virtually disappear.
Since we have to use treated water to
backwash the filters, this will provide
further savings.”
In June 2002, the City of
Englewood, Colorado, initially installed
a SolarBee unit in its 80-million (US)
gallon drinking water reservoir for
blue-green algae control. For years
copper sulphate had been applied typically
once or twice a week.
Another primary reason for
installing the units was concern about
the buildup of very dense sedimentation
over a 50-year period. “Over the
years there were attempts to clean the
reservoir out with various types of
dredges and an aerator, but these
couldn’t keep up with the sedimentation,”
explains Don Coatman, Water
Production Superintendent at
Englewood Water District. Englewood
Water District faced a choice of draining
the reservoir, scraping out the sediment
and hauling it away – a process
that would cost hundreds of thousands
of dollars – or finding a less expensive
approach. The SolarBee system was
suggested.
To reduce sediment, the unit’s
down-hose is set below the thermocline
and close to the bottom where it pulls
large volumes of water and spreads
them across the surface. Since the
water from the bottom (hypolimnion)
layer is colder and denser than the top
layer, it aerates for a relatively short
distance (depending on temperature
differential), and then sinks to the bottom
again. This newly aerated water
oxygenates the nutrients in the sediment,
helping to break it up and alleviate
anoxic bottom water conditions.
The 10,000 (US) GPM SolarBee
unit was positioned in the area of the
sediment buildup. “It’s reduced sediment
in our reservoir probably by 75
percent,” Coatman says. “It has broken
it down and distributed it out. Because
the clean-up has eliminated the nutrients
in the sediment, it also helped get
rid of the blue-green algae problem at
the same time.”
The Englewood Water District is
also considering the installation of
these units in potable water storage
tanks. “With large storage tanks of
treated water you may have turnover
problems,” Coatman explains. “We use
chloramine treatment and if the water
sits in the tanks too long, nitrification
will occur, which could cause taste and
odor problems. So, by installing a
water circulation unit, the turnover
paddles in the enclosed tank (the solar
unit is mounted outside) keep that
water moving. This type of system is
also much cheaper than trying to put in
baffle units, pipe extensions or various
other remedies to the nitrification
problem.”
Ed Sullivan is a writer on technology
based in Hermosa Beach, California,
Contact e-mail: solarbee@solarbee.com.
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