Agitator or aerator for manure lagoons – this is a question that frequently arises in the market for equipment for managing swine and bovine manure. Both create movement in the lagoon. They both seem to do the same thing. But they work in completely different ways, and choosing the wrong one has direct consequences on the lagoon's performance and the value of the biofertilizer.
In this article, we explain what each piece of equipment does, why an aerator is not the right solution for rural manure lagoons, and what producers need to consider before making a decision.
*What is a stirrer and how does it work?*
The agitator is a mechanical device that moves the substrate within the lagoon.
It uses blades, propellers, or impellers that rotate and push the material, creating an internal flow that runs throughout the entire volume of the lagoon. This movement:
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It breaks the surface crust.
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It keeps the sediment at the bottom in suspension.
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It homogenizes the contents throughout the entire volume of the lagoon.
The tractor-mounted agitator, in the Cardan (power take-off) or hydraulic model, uses the tractor's power to generate this movement. It is a robust piece of equipment with high agitation efficiency, capable of efficiently moving large volumes of dense manure.
*Result:* A homogeneous lagoon, free of crust and compacted sediment, containing biofertilizer of uniform composition, ready to be pumped.
*What is an aerator and how does it work?*
An aerator is a device that injects oxygen into a liquid.
It works by forcing air into the substrate through:
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Rotating blades on the surface
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Submerged diffusers
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Compressed air jets
The goal is to increase the concentration of dissolved oxygen in the liquid to stimulate the activity of aerobic bacteria, organisms that need oxygen to break down organic matter.
*The aerator is widely used in:*
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Industrial wastewater treatment plants
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Wastewater treatment plants
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Stabilization ponds in series
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Activated sludge systems
In these contexts, where the goal is to reduce the organic load before discharge into a water body, aeration makes sense.
*In pig and cattle manure lagoons, where the goal is to preserve and use the biofertilizer, an aerator is not the appropriate solution.*
*Why the aerator doesn't work well in waste lagoons.*
*The aerator does not homogenize the lagoon.*
The movement created by the aerator is superficial and localized. The rotating blades agitate the top layer of liquid, but they don't have the power to move the denser material at the bottom, where sediment accumulates.
The crust may be partially broken at the surface, but sediment continues to accumulate at the bottom.
Practical result: the lagoon appears to be being worked on, but the usable volume continues to be compromised by sediment, and the biofertilizer remains stratified.
*The aerator reduces the cost of biofertilizer.*
This is the most critical point, and the least discussed.
Biofertilizer has agronomic value because it is rich in ammoniacal nitrogen, the form of nitrogen most readily available to plants.
When the aerator injects oxygen into the substrate, it stimulates nitrifying bacteria that convert ammoniacal nitrogen into nitrate and nitrite. Some of this nitrogen is lost to the atmosphere in the form of nitrous oxide, a greenhouse gas with a global warming potential far greater than CO₂.
*Result:* Biofertilizer from an aerated lagoon has a significantly lower nitrogen concentration than that from a well-agitated lagoon. The producer loses agronomic value and also pays for the equipment that caused this loss.
*The aerator cannot handle cattle manure.*
Cattle manure has a high fiber and suspended solids content. This material quickly clogs and damages aeration systems.
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Diffusers get clogged with fibers.
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Blades and rotors suffer accelerated wear.
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Maintenance becomes frequent and expensive.
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The equipment progressively loses efficiency.
The agitator, designed to work with dense substrates, does not have this problem.
*The aerator consumes more energy for less result.*
Aerating large volumes of liquid requires continuous and significant electrical energy.
In rural waste lagoons, which can have volumes of hundreds or thousands of cubic meters, the electrical consumption of a suitable aeration system is much higher than:
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Energy consumption of an electric stirrer
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Fuel consumed by the tractor during periodic agitation sessions.
*The cost-benefit ratio of aerators in rural waste lagoons rarely balances out.*
*An aerator makes sense when:*
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The goal is to reduce the organic load before discharge into a body of water.
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The system is a wastewater treatment plant.
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The substrate is industrial effluent or domestic sewage.
*An aerator is pointless when:*
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The goal is to homogenize the lagoon for pumping.
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The material will be used as biofertilizer in agriculture.
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The substrate is pig or cattle manure.
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The property needs to preserve the agronomic value of the material.
The producer who needs to homogenize the lagoon, preserve the value of the biofertilizer, and facilitate pumping needs agitation, not aeration.
*FAQ — Frequently Asked Questions*
*1. What is the difference between an agitator and an aerator for a waste lagoon?*
The agitator mechanically moves the substrate, homogenizing the entire volume of the lagoon. The aerator injects oxygen into the liquid to stimulate aerobic bacteria. These are pieces of equipment with different functions, for different purposes. For rural waste lagoons with agronomic use of biofertilizer, the agitator is the correct equipment.
*2. Can the aerator be used in a pig manure lagoon?*
It is not recommended. The aerator does not homogenize the bottom of the lagoon, where sediment accumulates. Furthermore, the injection of oxygen destroys ammoniacal nitrogen, the main factor of agronomic value in swine biofertilizer.
*3. Does the aerator work well with bovine manure?*
No. Cattle manure has a high fiber content that clogs diffusers and quickly damages blades and rotors. Maintenance costs increase and efficiency progressively decreases.
*4. Why does the aerator reduce the value of biofertilizer?*
Because the injection of oxygen stimulates nitrifying bacteria that convert ammoniacal nitrogen, the form most readily available to plants, into nitrate and nitrite. Some of this nitrogen is lost to the atmosphere in the form of nitrous oxide, a greenhouse gas.
*5. Does the aerator homogenize the lagoon?*
Not efficiently. The movement created by the aerator is superficial. It agitates the top layer of liquid, but does not move the sediment at the bottom. The biofertilizer remains stratified.
*6. Does the tractor-mounted agitator work with cattle manure?*
Yes. The tractor-mounted agitator is designed to work with dense substrates, including high-fiber bovine manure. Its robust structure and high-torque propeller ensure efficient homogenization even under demanding conditions.
*7. Which piece of equipment consumes less energy, the agitator or the aerator?*
The agitator. Aerating large volumes requires continuous and significant electrical power. The tractor-driven agitator uses the tractor's fuel in periodic sessions, and the electric agitator operates at much lower power than an equivalent aeration system.
*8. Where is the aerator the correct piece of equipment?*
In industrial wastewater treatment plants, sewage treatment plants, stabilization ponds in series, and activated sludge systems, the objective is to reduce the organic load before discharge into a water body.
*9. Does the agitator preserve the nitrogen in the biofertilizer?*
Yes. Mechanical agitation does not alter the chemical composition of the substrate. Ammoniacal nitrogen is preserved, ensuring greater agronomic value of the biofertilizer applied to the crop.
*10. How to choose between a tractor-driven agitator and an electric agitator?*
It depends on the property's profile. A tractor-mounted agitator is ideal for those who already have a tractor available, have adequate access around the pond, and perform agitation at specific times. An electric agitator is suitable for continuous or programmed agitation, without operator dependence.
*Summary*
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Agitator and aerator have completely different functions.
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The agitator mechanically moves the substrate, homogenizing the entire lagoon.
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The aerator injects oxygen, but it does not homogenize the bottom of the lagoon.
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The aerator reduces the ammoniacal nitrogen content of the biofertilizer, decreasing its agronomic value.
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Fibers from cattle manure quickly damage aeration systems.
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The energy consumption of the aerator is much higher than that of the agitator.
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For waste lagoons where biofertilizer is used for agricultural purposes, an agitator is always the right solution.
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The aerator is only suitable for wastewater treatment systems intended for disposal.
*Do you want to find out which agitator is ideal for your pond?*
AGTO manufactures tractor-mounted agitators in Cardan (PTO71, PTO70, PTO101, PTO100) and hydraulic (AH70) models, with different lengths and power outputs for different lagoon profiles. Our technical team analyzes the characteristics of your lagoon and recommends the ideal model to ensure efficient homogenization and preservation of the biofertilizer's value.
Get in touch and speak with an AGTO specialist.
