Algae problems are nothing new to water in the US. It’s a natural occurring part of the ecosystem, and most would agree it is an important component. However, the problems caused by an overgrowth of algae can be more of a nuisance than a benefit when it comes to dealing with the issues produced by algae overgrowth.
Common Types of Algae and why does it grow
There are three major groups of algae: Filamentous, Planktonic and Macroalgae. Among those groups, there are four different “kinds” of algae, which will make your water look different colors – Blue-Green, Green, Red and Golden.
The three most prominent algae types being treated in our lakes, ponds and reservoirs are blue-Green and Green algae and Diatoms, that can be either Planktonic, Colonial or Filamentous.
Filamentous algae are Single-Cell algae, that grow together to create long, “string-like” clumps of algae. They are more rigid in structure and can be picked up by hand.
Planktonic Algae are Single-cell microscopic algae either Green or Blue-Green, the latter which contain gas vesicles, allowing them to float to the surface to improve photosynthesis by absorbing light photons. Photosynthesis allows them to convert CO2 to CH2O being their primary organic building block. The algal cells are free-floating or swimming via flagella in the water or collect in colonies of surface scum. Examples of Planktonic algae are: Microcystis, Anabaena, and Aphanizomenon.
Microcystis is one of the leading culprits of Harmful Algal Blooms, or HABs, and has been the source of many national headlines around the US for its Microcystin Toxin releases, killing dogs and making humans sick, among other reports.
Macroalgae are very similar to plants and often time have stems and leaves. They will grow from the bottom of the pond, and depending on the depth of the pond, reach the surface. They are some of the most difficult algae to control and typically are mechanically removed.
Algae Growth can be caused by several factors, including but not limited to high nutrient load (i.e.: Nitrogen and Phosphorus), stagnant water, lots of sunshine, and warm temperatures. Now, you would think that all ponds in the warmer clients, for example, across the southeast, would have an algae problem based on these four causes. Truth be told, while algae has a presence in most water bodies, it’s the overgrowth of algae that really causes headaches in the form of higher pH levels, increased TSS and TOC, and can also lead to Harmful Algae Bloomsor HABs.
It is these bodies of water that will be examined more closely in the form of two case studies performed over the last two years, and the non-chemical algae control approach taken.
Non-Chemical approaches to Algae Control There are about 70000 species of algae and about 2 million types when sub-species are totaled, making it virtually impossible to test and analyze effective solutions for all algae types out there. In the past 30 plus years, a variety of solutions have been used for algae control, most commonly copper sulphate-based products. But there are also a number of non-chemical solutions on the market. Aeration, bacteria and barley straw are some of the more familiar solutions used today, with ultrasound technology rapidly becoming a trusted alternative around the world.
How ultrasound works to control and eliminate Algae
Ultrasound was introduced for algae control in the late 1990’s, when a group in Belgium wanted a non-chemical way to treat irrigation ponds for growing flowers. In their research, they found that specific ultrasound frequencies used underwater were able to breakdown microscopic and single-cell algae, preventing growth, reproduction, and regrowth, in their irrigation ponds. By preventing algal growth, the irrigation lines remained clear and no chemicals needed to be used.
Fast forward 20 years, and ultrasound has been widely used in various pond and reservoir applications across the world in over 100 countries. Ultrasound technology can now effectively treat areas as large as 120 acres with a single ultrasound transducer, for the blue-green algae type. Through many generations of ultrasound products from a small, select number of manufacturers, ultrasound is quickly becoming the go-to non-chemical alternative for algae control.
Soundwaves are emitted from the transducer head (apparatus that sits under the surface of the water that converts electrical energy into sound (mechanical) energy, inaudible to the human ear (ultrasonic)). These ultrasonic soundwaves, of over 2000 varying frequencies, hit the harmonic value of the single algae cell, causing internal wall damage via structural resonance. Like an opera singer, who can shatter different sized and shaped crystal glasses their voice. The frequency of the glass can be found by ringing it and when that frequency is sung back to the glass it reverberates with increasing intensity and breaks. Ultrasound works much in the same way in algae cells breaking internal walls or by cracking gas vesicles.
When the algae inner cell wall is torn, internally pumped fluid flow and internal pressure is disturbed causing collapse of the inner cell wall and loss of nutrient transfer. This causes loss of viability in Green algae and Diatoms in 3-4 weeks. In Blue-Green cells, gas from broken gas vesicles migrate to and diffuse out through the outer cell wall making it heavier than water in 3-4 days. Sinking out of light prevents it from further growth due to limited access to sunlight.
In essence, ultrasound is effective in preventing the algae from growing, eating and reproducing, starves the cells, which then sink to the bottom of the water application, and die off. It is important to note that, for detected HABs, ultrasound does not lyse the outer cell wall so residual toxins will not be released. Most Blue-Green generated toxins are made of groups or amino acids and supply the cell or colony with needed Nitrogen. Once out of light, it cannot generate more of these toxins.
Ultrasound technology for algae control is a 24/7 solution. The ultrasonic transducer head, which runs on just 44 volts, and draws only 11 watts of power, is placed in the middle or on the edge of the water body (depending on size and shape). The units are line-of-sight technology, therefore for any irregularly shaped bodies of water, multiple units may need to be installed. For maximum results, the entire water body would need to be treated.
Things to keep in mind
Ultrasonic waves targeting algae is a lengthier process than other chemical methods. Whereas you can see more immediate results from using a chemical solution, ultrasound is a slower, more permanent process. Be aware that ultrasound is not effective on all types of algae. For instance, ultrasound is not effective on macroalgae, or plant-like algae. The branching nature of the algae creates a natural defense mechanism that ultrasound cannot penetrate and disrupt. It is recommended that an algae identification be performed prior to installation to determine genus of algae in the water.
Lastly, as with most other solutions, ultrasound should be considered a “tool-in-the-toolbox”, and not a silver bullet solution. Like anything in nature, ponds and their water are ever changing, along with the surroundings, weather, run off and nutrient load. Sometimes a multi-faceted approach needs to be taken for optimal results. An example is called a Water-Trifecta®, where aeration, ultrasound and beneficial bacteria are all used simultaneously for overall health of the pond.
Practical Application – Case Study 1 – Utility Facility – 60 Day Holding Pond
The Attala Plant for Entergy® Corporation in Mississippi was experiencing seasonal algae blooms in their 60-day Holding pond in 2017. The utility plant water process is as follows:
In the past, Entergy® was unable to use “traditional treatment methods” (Copper Sulphate based algaecides), and because the 60-Day pond also receives runoff from local agricultural areas (nutrient load) the algae growth was getting worse each year. Affected water will then run into the 7-day pond, where optimal conditions exist for proliferation (shallow stagnant water, loads of sunlight).
The specific issues experienced at the Entergy® plant caused by this algae overgrowth were:
- Small, weak, light flocculation
- Clogged sand filters
- Biological fouling of the RO membranes and heat exchangers
- Excessive chemical consumption in the cooling towers to treat the increase biologicals
- Excessive costs to treat incoming raw water for plant use
The Algae Culprit
A sample of the algae was sent off to Mississippi State University for analysis and it was identified as Microcystis, a Blue-Green Algae. It was determined that this particular Microcystis sample did not have any toxins, and therefore was not considered an HAB.
The Trial Solution – Ultrasound
In 2017, Entergy® obtained and installed an ultrasound unit from SonicSolutions Algae Control, (SS-600 model) to install into their 60-day pond. The pond is approximately 11 acres, and 10 feet deep.
The Trial period was 90-days. After the first 30 days, the small algae bloom was noticeably dying and floating on the surface of the water.
After the 90-day trial was complete, Entergy® extended the use of the ultrasound unit and noticed the following results:
- Decreased TOC in the water and plant inlet water
- Decreased Labor in Clarifier operations
- Decreased chemical consumption
- Decreased Maintenance in Raw Water Supporting Systems
- Substantial Financial Savings
“This device is proven to be effective for a low-cost treatment of Blue-Green Algae and Green Algae in surface water,” says the treatment plant operator.
Practical Application – Case Study 2 – Drinking Water Reservoir – Wilmington, OH
In 2018, Wilmington, OH conducted a 90-day trial with side-by-side drinking water reservoirs, one treated with Copper Sulphate and one treated with ultrasound.
Reservoir 1 is 14 acres and was treated with a 360° ultrasound unit. Reservoir 2 is 50 acres and was considered the “Control” and treated with Copper Sulphate.
Historically, both reservoirs experienced both Blue-Green and Green Algae. Cylindrospermopsis and Microcystis (including Microcystin toxins) were the main concerns for treatment during the trial. Past treatments of the reservoirs were exclusively Copper Sulphate.
The goal of the 90-Day trial was to observe the effectiveness of the ultrasound units on the algae in the reservoirs, in order to reduce chemical usage and costs. There were weekly algae sampling and water quality tests performed by the EPA and observed by Ohio State University.
After 60 days, the reports showed that there were no algae in the actual water column, however there was still evidence of toxins along the rock-bed sides and in the silt at the bottom. It was concluded that past residual algae toxins were embedded in the bottom, causing it to show up in reports, but there were no new algae growing. They also concluded that ultrasound was just as effective as Copper Sulphate for controlling the algae in the reservoir.
Rick Schaffer, superintendent of the Wilmington Water Treatment Plant states: “The reservoir with the ultrasonic unit is certainly clearer than it has been historically, and it has an overall lower cyanobacteria count…The Smaller Reservoir (Res 2) is almost tropical, it looks so clear. It looks as good as it does the night after a copper treatment”.
At the end of the 90-day trial, the City of Wilmington purchased a second 360° ultrasound unit to treat the larger Reservoir 2.
Advantages and Disadvantages to Ultrasound technology for algae control
Ultrasound has been a proven technology in the US for Blue-Green and Green algae types for the past 17 years. There are significant cost savings in labor and chemical costs, and requires minimum electricity or can run on solar, which can add to the cost savings. Ultrasound can be used in both small and large applications, can cover 120 acres with a single 360° unit, and shows no effect on other wildlife or plant life.
Ultrasound is, however, limited in that it does not treat all blue-green and green algae. It is recommended that an algae genus identification be obtained prior to installation. The technology is line-of-sight, therefore if there are any obstructions (islands) or coves in the reservoir, then multiple units may need to be added for full coverage.
George Hutchinson, CTO
Devon Assael, VP Sales & Marketing