Aeration energy savings, measured and independently verified
Aeration is the largest single electricity use at most wastewater treatment plants. Ekster & Associates' control systems reduce it by supplying only the air the biological process needs, with the plant's existing blowers. Operators can override the system at any time, and faulty instrument readings are not acted on.
Verified savings
Pomona Water Reclamation Plant, Los Angeles County Sanitation Districts. U.S. Department of Energy funded demonstration, led by Carollo Engineers (final report DE-EE0009509, 2025).
| Measure | Value |
|---|---|
| Aeration energy, whole project | 1,300 kWh/MG before, 550 kWh/MG after |
| Contribution of new blowers | 34% |
| Further contribution of lowering dissolved oxygen with DO/Nmaster and SRTmaster | 30% of blower energy |
| Blower energy, DOE techno-economic metric | 999 kWh/MG (June 2019 – June 2020) to 520 kWh/MG (September 2024); DOE target 650 kWh/MG |
The two baselines cover different periods and measures in the report: 1,300 kWh/MG is the project baseline for aeration energy, and 999 kWh/MG is the baseline of the techno-economic analysis (June 2019 – June 2020).
City of Chico, California (12 MGD design). Verified under PG&E's California Wastewater Process Optimization Program (CalPOP) by QuEST, a third-party engineering firm (post-installation verification report, August 2018).
| Measure | Value |
|---|---|
| Aeration power per pound of daily oxygen demand (kW/lb) | 0.02392 before, 0.01254 after (47.6% reduction) |
| Verified electricity savings | 1,198,692 kWh a year |
| Electricity cost savings | $168,051 a year (2018 rates) |
| PG&E incentive paid to the City | $121,208 |
| Baseline and post-installation periods | 20 January – 10 February 2015; July 2018 |
| Measures installed in 2018 | DO/Nmaster; 15 automated valves; 15 airflow meters; 3 ammonia meters; dissolved oxygen meters increased from 6 to 15; centrate storage with night-time injection; improved blower sequencing |
| Blowers and diffusers | Existing; not replaced |
Chico's aeration energy is 580 kWh per million gallons treated (kWh/MG), against an industry average of 800–1,500 kWh/MG, both aeration energy only.
Estimating savings for your plant
The saving depends mainly on how much the dissolved oxygen can be lowered. At Pomona, lowering dissolved oxygen from 2.5 mg/L with DO/Nmaster and SRTmaster saved a further 30% of blower energy after the blowers had been replaced (U.S. Department of Energy final report). The free plant assessment estimates the saving for a specific plant from its own operating data and energy bills.
Measurement and verification
- Normalized results. Savings are stated per unit of treatment (kWh per million gallons, or kW per pound of oxygen demand), so that changes in flow and load are not counted as savings.
- Stated periods. Every result gives the baseline and post-installation periods.
- Equipment changes separated. Where equipment changed during a project, as at Pomona, the contributions of the equipment and of the control system are reported separately.
- Utility program support. The Chico project was verified and paid an incentive under a utility energy efficiency program. Ekster & Associates provides the operating data and documentation that program verifiers require. Eligibility and incentive levels depend on the local utility's program.
Avoided emissions
Avoided CO₂e is calculated from the electricity saved, using the EPA eGRID emission factor for the plant's region. At Chico, the verified saving of 1,198,692 kWh a year corresponds to about 234 metric tons of CO₂e a year, using the eGRID2023 factor for California (CAMX subregion, 430.0 lb CO₂e per MWh). The U.S. average factor is 770.9 lb CO₂e per MWh.
Next step: a free plant assessment
Send one year of operating data and energy bills. You will receive a written estimate of savings in kWh and dollars, the assumptions behind it, any changes required before installation, and a fixed price. If your plant is already operating efficiently, the estimate will say so.