Find Your Fit: Three Steps to the Right Aerator

Selecting an aerator can seem like a daunting task. Whether you are designing the basin and sizing the equipment from scratch or purchasing replacement equipment, there are some key points to consider. This page will help you through this process.

1. Know Your Pond or Basin

This is probably the most critical piece of information to know in selecting the correct aerator. The information which you will need includes:

• Size (length, width, depth) of the basin or pond:. This dictates the scale of the aeration needed. The type of aerator that can be selected depends on the liquid depth. High speed aerators tend to be for ponds with depths of about 1.5 m. For deeper ponds, low speed aerators can be considered.
• Shape of the basin: Irregular shapes might require multiple smaller aerators or specific placement.
• Current water levels and variations: Aerators need to be correctly submerged to function optimally. Fixed mounted aerators need to accommodate varying liquid levels. If water levels fluctuate significantly, consider floating aerators.
• Existing infrastructure: Consider the available power supply. Typically 400 V, three-phase power is required to power the motors to drive the aerators.
• Supporting structure: Evaluate the type of available supporting structure. This will limit the type and size of aerator. If there is no structure, then floating aerators need to be considered.

Gathering drawings, photos and basic sketches of the area can be incredibly helpful for suppliers.

2. Estimate Aerator Size

If you are supplying an aerator to an existing plant, you can determine the requirements from existing aerator unit nameplates. Site documentation should also be able to help.

Here we provide two ways of estimating the size of aerator required to provide sufficient aeration. The first is based on the size of the basin and the second is based on basic wastewater data.

2.1. Estimating size based on oxygen requirements

It is preferable to size the required aerator on the oxygen requirements. Required oxygen is measured in grams per cubic meter. A water sample can then be taken to determine key information including:

• Biological Oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Oxygen for Nitrification

It is also important to know the retention time of the water in the basin or pond.

The total oxygen required is about 4.6x the ammonia-nitrogen and 1.5x the BOD. Divide this this by the number of hours the water spends in the basin to get the oxygen required in kilograms of oxygen per hour (kg/hr). This provides valuable information to accurately estimate the required aerator size.

2.2. Estimating size based on basin/pond size

When the aerator oxygen requirements are known, the design can be based on the size of the pond or basin. The following information can be used as a guide:

• Pond: A pond typically has a long retention time. This means, that there is more time to oxygenate the water. If the depth of a pond is < 1.5 m then a high speed aerator with a minimum of 4W/m³ should be sufficient. Depending on the size of the pond and the water quality, multiple aerators might be required per pond.
• Basin: Usually, wastewater has a shorter residence time in a basin compared to pond. Therefore, the aerator is required to oxygenate the water faster. If the basin depth is between 3m and 6m, then a low speed aerator can be considered. Typically, the size required would be around 40 W/m³. Low speed aerators, are more efficient than high speed aerators meaning that they transfer more oxygen to the water for the same size motor.

The required power per cubic meter of water is dependent on the quantity of oxygen required by the process, as well as the retention time which determines how quickly the water needs to be aerated. Depending on the pond or basin size, the power calculated above can be be split across multiple aerators.

These sizing rules should be used as a general guide to providing an indication of what to expect.

3. Consider Project Requirements

Estimating power and oxygen requirements is just the first part of an aerator selection. Below is a list of some additional details relating to your larger project requirements to consider.

• Lead time: Aerators are not off-the-shelf items and you can expect a lead time of 6-8 weeks on smaller units and up to 24 weeks on larger units. This needs to be considered in project planning
• Materials of construction: Consider the materials of construction and corrosion protection of wetted parts, based on the composition of the wastewater.
• Extras: These include motor and gearbox special requirements, any site specifications, aerator accessories like draft tubes, pontoons, mooring cables, electrical cables
• Delivery, installation and commissioning: Zentec can assist here on request

Ready to Contact Zentec

Now that you understand some of the information required to select the perfect aerator, you are ready to contact Zentec for a quote. Please provide as much information to us as possible to help us assist you better. Useful information includes:

• Basin dimensions
• Water quality
• Estimated aerator size in power (for example 30 kW)
• Number of aerators required
• Site location