Controller
The electronic controller generates and manages the electrical signals used to produce the ultrasonic frequencies. Depending on the system, operating frequencies may be fixed, varied or selected for different algae groups.
The basics
How ultrasonic algae control works
Ultrasonic algae-control systems use low-power sound waves above the range of human hearing. The equipment operates in the water for long periods, transmitting selected frequencies intended to interfere with structures or biological processes in algae and cyanobacteria.
Start here
What does “ultrasonic” mean?
Sound is vibration traveling through a material such as air or water. Frequency describes how quickly those vibrations repeat and is measured in hertz (Hz). Human hearing is usually described as extending to roughly 20,000 Hz, or 20 kHz. Sound above that range is called ultrasound.
Commercial algae-control systems commonly work in ultrasonic frequency ranges beginning around 20 kHz and extending into the hundreds of kilohertz. Rather than transmitting one frequency continuously, modern systems typically cycle rapidly through a programmed set of many frequencies. The number of available frequencies has increased substantially as the technology has developed—from relatively small sets in earlier equipment to hundreds or thousands of discrete frequencies in newer designs.
This frequency specificity is important. Algae and cyanobacteria differ in size, cell structure and internal features, and particular structures can respond more strongly when the applied sound is close to a responsive or resonant frequency. A closer frequency match can produce a greater physical effect without simply increasing acoustic power. Modern systems therefore emphasize repeated, targeted frequency sweeps rather than a single frequency or brute acoustic power.
Low power is an important distinction.
Pond and lake algae-control systems are generally designed for continuous, low-power operation. They should not be confused with powerful ultrasonic laboratory probes, cleaners and industrial sonication equipment capable of producing intense cavitation and physically breaking cells apart.
The equipment
What is an ultrasonic algae-control system made of?
Ultrasonic transducer
The transducer converts the electrical signal into mechanical vibration and transmits ultrasonic pressure waves into the water. The transmitting head is submerged near the surface and positioned with a relatively open acoustic path across the treatment area.
Power source
Systems may use shore power or solar power. Because field systems are designed for low-power continuous operation, their electrical demand can be modest compared with many mechanical water-treatment devices.
Larger installations may use multiple transducers or floating stations. More sophisticated systems can also include water-quality sensors, telemetry, remote monitoring and software that changes ultrasonic programs in response to conditions.
How is the transducer installed?
For a typical shore-powered installation, the transducer is suspended beneath a small float so the transmitting head remains at the intended depth below the surface. The float is held in position with an anchor, mooring line or similar restraint while the power/control cable runs back to the shore-based controller.
Remote sites may use a floating solar platform or raft that carries the solar panels, batteries and control equipment while the ultrasonic transducer operates beneath the platform. Larger lakes and reservoirs can use multiple anchored floating stations positioned to provide the required acoustic coverage.
The exact mounting arrangement varies by system, but the basic objective is the same: keep the transducer submerged at the proper depth, securely positioned and facing an open treatment area with as few physical barriers as practical.
In the water
What happens after the transducer turns on?
The transducer produces rapid pressure oscillations that travel outward through the water as sound waves. Because water carries sound efficiently, ultrasonic energy can propagate well beyond the transducer itself.
The biological effect depends on the frequency, acoustic intensity, exposure time and the organism being exposed. Different algae have different sizes, shapes, cell walls, colonies and internal structures, so they do not all interact with ultrasound in the same way.
Continuous field systems typically expose algae repeatedly as cells remain within or move through the effective acoustic field.
Algae biology
How can ultrasound affect algae?
Gas vesicles
Many bloom-forming cyanobacteria use microscopic gas-filled structures called gas vesicles to regulate buoyancy and position themselves where light and nutrients are favorable. Research has shown that appropriate ultrasonic exposure can affect these structures. Loss of buoyancy can move cells away from favorable light conditions.
Growth and photosynthesis
Experimental studies have reported changes in growth, photosynthetic activity and cellular function after ultrasonic exposure. The response depends strongly on the organism and ultrasonic conditions.
Different cells respond differently
Cyanobacteria, planktonic green algae, diatoms, dinoflagellates and filamentous algae are structurally different. Cell walls, filaments, colonies and other physical characteristics influence how an organism interacts with sound.
An important misconception
Low-power field ultrasound is not intended to “blast” algae apart.
Some laboratory studies use much higher acoustic energy specifically to rupture cells. That process may involve cavitation — the formation and collapse of microscopic bubbles that can generate intense local forces.
Typical continuous pond and lake systems use far lower acoustic power and are designed to operate without destructive cavitation. Their operating concept is repeated exposure to selected frequencies rather than physically shredding organisms with high-energy ultrasound.
This distinction also matters when reading research. A laboratory experiment using high-power sonication may teach us something about algae biology without describing what happens around a low-power field transducer.
Coverage
How far does the sound travel?
Ultrasound can travel considerable distances through water, but sound transmission distance and effective algae-treatment coverage are not the same measurement.
Acoustic energy decreases with distance. Suspended solids, bubbles, vegetation, shoreline shape, islands, walls and other physical conditions can affect transmission. A long narrow pond, an open circular pond and a reservoir full of coves may therefore require very different layouts even if they contain the same surface acreage.
Commercial system coverage is consequently specified by the equipment manufacturer and system design, usually as an approximate radius, area or volume under suitable conditions. Larger or irregular waterbodies may require multiple transducers.
After exposure
Where do the algae — and their nutrients — go?
When buoyant cyanobacteria lose their preferred position in the water column, they may settle or spend more time below the light-rich surface zone. Other affected algae may experience inhibited growth or altered cellular function. Dead or declining biomass is eventually processed by the pond or lake ecosystem.
The nutrients contained in that biomass do not simply disappear. Phosphorus and nitrogen remain part of the aquatic nutrient cycle unless they are physically removed, permanently bound, exported from the system or otherwise made unavailable. For that reason, ultrasonic equipment and nutrient management address different parts of an algae problem.
Aquatic life
What about fish, zooplankton and aquatic plants?
Low-power algae-control systems operate at acoustic intensities far below high-energy sonication equipment. Published field research using a 7–9 watt, dual-frequency system (23 and 46 kHz) exposed common carp for 30 days and found no ultrasound-related effects in the biological measures evaluated.
Other field evaluations have examined zooplankton exposed to commercial low-power systems, and controlled field work has monitored non-target plankton alongside cyanobacteria. Safety conclusions should always be tied to the frequency, power and exposure conditions actually tested rather than generalized from the word “ultrasound” alone.
Keep the technologies separate
What an ultrasonic system does — and does not do
It is not an aerator
Ultrasound does not add dissolved oxygen or circulate the entire water column in the way a properly designed aeration system does.
It is not an algaecide
No copper, peroxide or other algae-killing chemical is being dosed into the water by the ultrasonic unit.
It is not nutrient removal
The device does not remove incoming phosphorus or nitrogen from the watershed. Nutrient reduction and ultrasound are separate management processes.
Go deeper
From the technology to the research
Once the basic technology is clear, the research library examines laboratory studies, field trials, documented applications and user experiences in greater detail.
Explore the research library