Industry
Blowers for wastewater aeration: types and energy use
A 2010 US EPA report describes wastewater aeration blowers as low pressure, high volume air compressors, commonly positive displacement or centrifugal, that feed diffused aeration systems, and, citing WEF, puts aeration at 25 to as much as 60 percent of total treatment plant energy use.
Where the air goes
The 2010 EPA report on energy conservation measures for wastewater treatment facilities explains that wastewater is aerated by bubbling air or high-purity oxygen through it, or by mixing it, and that the two most common systems are diffused aeration and mechanical surface aeration. A diffused aeration system has an air intake, typically with filters that protect the blowers and diffusers from airborne particulates, the blowers, the air piping, the diffusers and controls. Headloss in the air piping is typically less than 10% of total system pressure.
Blower types
| Type | Typical flow and pressure | Notes from the EPA report |
|---|---|---|
| Positive displacement | 5 to 50,000 scfm, 1 to 14 psig | Fixed volume of air for every shaft revolution; low capital cost, economical at small scale; difficult to operate at variable flow rates without a VFD, can be noisy, needs more maintenance and is typically least energy efficient |
| Centrifugal, multi-stage | 500 to 30,000 scfm, 4 to 14 psig | Can be more energy efficient than positive displacement; efficiency decreases with turndown |
| Centrifugal, single-stage, integrally geared | 500 to 70,000 scfm, 4 to 24 psig | Can be more energy efficient than multi-stage or positive displacement and can maintain good efficiency at turndown; higher capital cost |
| Centrifugal, single-stage, gearless (high-speed turbo) | 400 to 10,000 scfm, 4 to 35 psig | Small footprint; efficient for lower air flow ranges; described in 2010 as a new technology with limited experience |
The EPA report takes these figures from WEF (2009) and from WEF and ASCE (2010).
Matching air to oxygen demand
The EPA report says the aeration process can account for the largest energy demand of any operation at the facility, although the demand is site-specific and can vary widely from plant to plant. Energy savings can be gained by designing and operating aeration to match, as closely as possible, the actual oxygen demand of the process. The closer the dissolved oxygen concentration is to saturation, the lower the oxygen transfer efficiency, and fine-pore diffusers have the highest efficiency of any diffused air or mechanical aeration system. Conventional measures include proper sizing of blowers, dedicated blowers for channel aeration and the configuration of diffusers in the basin.
The US Department of Energy compressed air sourcebook (2016) lists sparging, which includes aerating or oxygenating a liquid with compressed air, among potentially inappropriate uses of compressed air, and names low-pressure blowers and mixers as alternatives.
Ultra Controlo
Ultra Controlo distributes and services the Gardner Denver and Elmo Rietschle ranges, which both include blowers in the Industrial 2026 catalogue; the catalogue does not link them to wastewater treatment. Where oxygen rather than air is used, the ULTRAOX VSA datasheet lists wastewater treatment plants among its applications; see oxygen for wastewater treatment.
More questions
Which blower type is least energy efficient?
The 2010 EPA report describes positive displacement blowers as typically least energy efficient, and says centrifugal blowers can be more energy efficient than positive displacement.
Can oxygen replace air for aeration?
The 2010 EPA report notes that wastewater is aerated by bubbling either air or high-purity oxygen through it. The ULTRAOX VSA datasheet lists wastewater treatment plants among its applications; the plant delivers 75% to 95% oxygen at 50 kPa.
Sources
- US EPA, Evaluation of Energy Conservation Measures for Wastewater Treatment Facilities, EPA 832-R-10-005 (September 2010), chapters 4 and 5
- US Department of Energy and Compressed Air Challenge, Improving Compressed Air System Performance: A Sourcebook for Industry, Third Edition (2016), Fact Sheet 2
- Ultra Controlo, Industrial 2026 catalogue, pp. 10 and 11
- ULTRAOX VSA datasheet, pp. 2 and 3
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.