Dynamic Blower Technologies Innovations for Wastewater Treatment Plants

The aeration system blowers account for over 50% of the energy consumption at a wastewater treatment plant. Energy is typically the largest operating expense at a treatment plant, second only to labor costs. Hence, there is no other equipment that will impact overall operating cost more than the selection of the aeration blowers.

During the last 20 years, with the steady increase in energy costs along with treatment processes that require wide ranges of airflow, the wastewater industry has progressively gravitated toward high efficiency centrifugal/dynamic blower technologies for their aeration systems.

The three centrifugal blower technologies utilized, today, in the water treatment industry are as follows: Multistage, Gearless Turbo and Geared Turbo

Contact Lone Star Blower & Compressor

Multistage Centrifugal Blowers

This technology consists of a series of impellers mounted on a shaft supported on each end by roller bearings. The blower shaft is directly coupled to a 2-pole motor (3,600 rpm). The casing directs the air (gas) from one stage (impeller) to the next. Each stage increases the air pressure. In the aeration system of a wastewater plant, anywhere from 3 to 9 stages are utilized depending on blower size and discharge pressure requirements. 

Figure 2

Flow modulation for this technology is achieved either through an inlet throttling valve or a variable frequency drive.

This technology has been the workhorse for the wastewater industry and for several low pressure air and gas processes in industrial applications.


  • Simple mechanical construction
  • Non-proprietory components
  • Ease of installation and maintenance
  • Maintenance through non-OEM
  • Low operational speed
  • Low operating noise (<88 dBA)
  • Long life expectancy
  • Ability to withstand multiple surge events
  • Available in different voltages

Historical Limitations:

  • Lower compression efficiency at off-design points with respect to turbo centrifugal technologies
  • Casing air leakage
  • Reduced bearing life expectancy (4-6 years of operation)
  • Reduced turndown
  • Limitation on design discharge pressure (approximately 15 psig at sea level)

In the last few years, the design of this technology has been improved by certain manufacturers to overcome some of the historical limitations:

Recent Design Improvements

  • Viton O-ring seals between casing stages in lieu of silicone to eliminate air lekeage
  • High flow shaft driven cooling fan on discharge bearing and balancing drum to enhance bearing life
  • Larger impeller diameters with backward leaning blades to increase turndown and discharge pressure capabilities (> than 20 psig at sea level).
Figure 3

Gearless Turbo Centrifugal Blowers

This technology is a single-stage blower: The compression work is done with a single impeller rotating at high speed (typ. 20,000 to 40,000 rpm). The impeller is mounted on the motor shaft; hence, the motor and the blower are integral to one another. This technology utilizes a high speed permanent magnet motor driven by a high frequency VFD. The bearing design are airfoil type*. This technology derived from the aeronautical industry and started to be utilized in the aeration system of wastewater treatment plants in the early 2000’s.

Figure 4


  • Ease of  installation and maintenance
  • Small footprint
  • Integral motor starter
  • Low operating noise (<85 dbA)
  • Higher efficiency with respect to positive displacement blowers and multistage centrifugal blowers
  • No oil or grease needed

Historical Limitations:

  • Low bearing life expectancy / idle mode required in some designs
  • Large heat rejection to be evacuated
  • Limited HP rating per blower core (<350 Hp)
  • High cost of proprietary replacement components

*note: This technology can also utilize magnetic bearings. Please see “A Quick Review of Geared and Gearless Turbo Blower Bearing Technologies” for advantages and disadvantages of airfoil and magnetic bearings.

  • Low voltage option only
  • Very sensitive to “dirty” power supply
  • Sensitive to surge episodes
  • Harmonic filters recommended
  • Sensitive to environmental conditions especially high elevation, coastal conditions, dusty environments and presence of corrosive gases

In the last few years, the design of this technology has been improved by certain manufacturers to overcome some of the historical limitations:

  • Triple treatment bearing design which allows for life expectancy from 25,000 to 100,000 start/stop cycles and better handling of surge episodes
  • Motor cooling shaft mounted fan (opposite to impeller) to evacuate motor heat avoiding blower heat ingestion – no liquid cooling required
  • Above referenced bearing and heat evacuation improvements allows for a HP rating of a single core up to 500 HP
  • Non-proprietary component design
Figure 5

If the site has “dirty” power, aggressive environmental conditions or the site is located at an elevation above 1,500 meters (4,920 ft), other blower technologies should be considered.

Geared Turbo Centrifugal Blowers

This technology is a single-stage blower: the compression work is done with a single impeller rotating at high speed (typ. 10,000 to 20,000 rpm). This technology utilizes a one-step gearbox mounted integral to the blower casing to increase the input motor speed (typ. 2-pole motor operating at 3,600 rpm) to the required impeller speed. This is a constant speed technology that utilizes internal vanes (one set of vane at the inlet and one set at the impeller discharge) to modulate flow and maximize compression efficiency at different operating conditions. The vanes are automatically positioned by the blower PLC, based on required airflow and onboard instruments monitoring inlet temperature and discharge pressure. This technology utilizes pressure lubricated journal bearings (some manufacturers use ball bearing in smaller frames and on low-speed shaft). 

Figure 6

For a quasi-constant head application, such as the aeration tanks of a wastewater treatment plant, the constant speed operation with internal vane provides efficiency and turndown benefits with respect to a variable speed control blower technology. Please refer to the blower operating graphs detailed below in figure 7.

Figure 7


  • Typically this technology offers the lowest operating costs
  • Wide turndown capability (from 100% down to 35-40% capacity)
  • Wide range of design discharge pressures (up to 30 psig at sea level)
  • Rugged design capable to operate in harsh environments
  • Long life expectancy
  • Ability to withstand multiple surge events
  • Available in different voltages
  • Non-proprietary components

Historical Limitations:

  • Radial blade impellers with limited rise to surge
  • Sticking vanes
  • Bearing replacement costs
  • Oil change
  • Noise level (>90 dbA) – will need sound enclosure to attain 85 dBA
  • High Capital Costs
Figure 8

In the last few years, the design of this technology has been improved by certain manufacturers to overcome some of the historical limitations by gravitating toward the original construction guidelines of this technology:

American Petroleum Institute API 672:

  • Backward leaning blades impeller design allows for rise to surge over 1 psi (10-15% of design pressure as required by API) versus the typical 0.2 psi rise to surge of radial impellers
  • Stainless steel internal vanes and stainless steel discharge plate (as recommended by API) avoids oxidation/corrosion and material heat expansion, which are the main causes of sticking vanes.
  • Tilting pad steel backed bearing design (as recommended by API) in lieu of fix pad bronze bearings and roller bearings eliminating the need to replace bearing throughout life of the unit.
  • Synthetic oil with 90,000 hrs. of operation minimizes oil changes requirements.
  • US manufacturing of components and increased competition allow for affordable equipment costs for this technology.
  • Affordable factory maintenance programs

Which one to Choose

Selecting the right blower technology for your plant is paramount for the ability to reliably, effectively and efficiently treat wastewater. When looking at wastewater treatment plants from 3 MGD up to 20 MGD all three centrifugal technologies can be a good fit. The ultimate selection has to be based on the selection criteria important to the end user. As summarized in figure 9, typically, the geared turbo blower present the lowest 20-year operating costs (energy + maintenance costs cost). On the other hand, multistage typically offer the lowest capital cost (equipment + installation costs). Site conditions and  end-user operation and maintenance idiosyncrasies are also important aspect to consider when selecting the right blower technology.

Figure 9

About the Authors:

Amber Roberts is a mechanical engineer with over 15 years of experience in rotating equipment.

Alessandro Lequio is a mechanical and electrical engineer with over 20 years of experience in rotating equipment.