Plant Optimisation
Energy Efficiency
Aeration is typically the single largest electricity consumer at a secondary plant. Targeted measures cut energy without compromising effluent quality.
Where the Energy Goes
Aeration supplies oxygen to the biology and often accounts for around half of total plant electricity use. Because it runs continuously and moves large volumes of air, modest efficiency gains in blowers and dissolved-oxygen control translate into significant, ongoing savings — while pumping and sludge handling make up much of the remainder.
Aeration Share
Typical share of plant energy
Aerobic DO Setpoint
Typical target for BOD + nitrification
Energy-Neutrality Objective
Recast Directive (EU) 2024/3019
Efficiency Measures
Dissolved-oxygen control
Match airflow to real oxygen demand instead of running fixed, over-conservative aeration. Most-open-valve strategies and demand-based DO setpoints avoid the large waste caused by chronic over-aeration.
Fine-bubble diffusers & efficient blowers
Fine-bubble diffusers deliver higher oxygen transfer efficiency; high-efficiency or turbo blowers with proper turndown reduce the electricity needed to deliver that air. Worn or fouled diffusers quietly erode efficiency over time.
Energy recovery from sludge
Anaerobic digestion of sludge produces biogas that can be converted to electricity and heat on site, offsetting plant demand and supporting the sector's energy-neutrality objective.
Engineering Note
Frequently Asked Questions
Aeration supplies oxygen to the biology and is typically the single largest electricity consumer at a secondary treatment plant, often around half of total plant energy. Because it runs continuously and moves large volumes of air, small efficiency gains in blowers and dissolved-oxygen control translate into significant energy and cost savings.
Common measures include dissolved-oxygen (DO) control that matches airflow to real demand, fine-bubble diffusers with higher oxygen transfer efficiency, high-efficiency or turbo blowers, most-open-valve control, and avoiding over-aeration. These reduce energy while maintaining the DO needed for BOD removal and nitrification — typically a setpoint around 2 mg/L in the aerobic zone.
The recast Directive (EU) 2024/3019 introduces energy-neutrality objectives for the urban wastewater treatment sector, to be reached progressively by 2045, together with energy audits. This makes aeration optimisation, biogas recovery from sludge and overall energy management central to compliant plant design and upgrades.
Engineering Assessment
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