Surface aerators are one of the most often utilized wastewater lagoon aeration technologies. When making any buying decision, it’s always important to be well informed. Below you will find a full breakdown of surface aeration as it relates to wastewater lagoon treatment.
The 3 Main Types of Surface Aerators
- Horizontal Aspirator – This variety of wastewater lagoon surface aerator is comprised of a motor aligned horizontally 45 degrees or more. A hollow shaft with a propeller tip connects to the motor and rotates on ball bearings. Aeration of the water occurs below the surface of the water as the motor rotates the propeller and air is pushed down the shaft and into the basin where it is turbulently churned into the water.
- Vertical “Splash” Aerator – This surface aerator gets its name from its vertically aligned motor. A propeller at the bottom of the motor spins and draws water from underneath the unit, and then launches it into the air in a circular pattern. Water aeration occurs above the surface as the small droplets of water fall back to the basin; the large collective surface area of the droplets allows for contact between water and ambient air, facilitating oxygen transfer.
“Jet” Surface Aerator – This brand of surface aerator is essentially a hybrid of the vertical and horizontal aerators. Like the horizontal aerator, its motor is located off-axis and aeration is achieved via drafted air or injected with a blower. Like a vertical aerator, water is drawn from a propeller and expelled across the surface, using the droplet-to-air contact to transfer additional oxygen.
The Benefits of Surface Aeration (Pros)
Below are a few of the main benefits of choosing surface aeration to treat your wastewater lagoon.
- Portable – Surface aerators simply float on the water and are held by moorings attached to onshore anchors. As a result, moving the aerator is rather simple; the unit is simply disconnected from its moorings and pulled to the new location.
- Easy Installation – Since these aerators are portable and require no subsurface mounting, installation is simple. You can place them in their location without draining the cell, secure them with moorings, connect electric cables, and be off and running.
- Good in Rough Environments – These aerators are composed of type 304 or 316 stainless steel, and are heavily resistant to corrosive wastewater. This makes surface aeration suitable for the most extreme environments (such as industrial pulp and paper plants, chemical industry, etc.)
- Good in Shallow Water – Surface aeration treatment takes place exactly where you would think it would—the surface. As a result, the shallower the water, the more directly affected the entire water column can be.
- Less Affected by Surfactants – Surfactants are substances that line the surface area between air and water, creating a barrier to oxygen transfer. These aerators largely avoid this problem by forcing the bubbles into the water and “churning” them up with a propeller, thus decreasing the influence of the surfactant.
The Disadvantages of Surface Aeration (Cons)
Conversely, here are some of the main disadvantages of choosing surface aeration to manage your wastewater lagoon.
- High Maintenance Requirements – These surface aerators rely on constantly moving motors on the surface of the water to operate properly. As a result, the potential for breakdown increases. For this reason, mechanical aerators have a much higher malfunction rate than other systems. It is recommended that each surface aerator be serviced biannually. Given that wastewater lagoons typically use 5–10 surface aerators and they can only be serviced from a boat, this maintenance job becomes a hassle. Furthermore, by installing a system prone to malfunctioning, you risk excessive facility downtime.
- Inefficient Aeration – Independent testing facilities have shown surface aerators to transfer just 1.25–2.25 pounds of oxygen per horsepower hour. This is compared to diffused aeration systems, which can impart as much as 6–7 lb/hp-h. As a result, Surface Aerators have higher power requirements and cost more to run.
- Limited Mixing Performance – A surface aerator can really only mix the water in its immediate vicinity. Treatment is generally completed by only a few surface aerators per wastewater lagoon. As a result, “dead zones” tend to develop where water stagnates and sludge accumulates. The only way to increase mixing is to add additional aerators at an increased capital and operational cost. Our article Wastewater Mixing Alleviates Odor & Sludge Issues is a case study illustrating the importance of lagoon mixing.
- Ineffective in Deep Water – Since the aeration takes place on the surface, the deeper water columns see little to no treatment. This allows solids to accumulate, virtually untouched by the aerator. The addition of draft tubes can help some, but even so the area of influence is very limited horizontally across the surface.
- Trouble in Cold Weather – In cold temperatures, water churned up by surface aerators freezes when it is exposed to ambient air. The combination of splashing water, and being exposed to freezing rain and snow, makes these motors prone to failure in cold weather. It is for this reason that some northern states have banned the use of mechanical aeration in new plants. Our blog, Winter Wastewater Lagoon Operations: Is Your Lagoon Ready?, outlines some of the challenges lagoons face when temperatures drop.