Aeration tank blowers at a municipal wastewater plant
The customer
A municipal wastewater treatment plant treating 35,000 m³/day for a town of 90,000 residents. The activated-sludge process needs continuous air injection into the aeration basins to keep dissolved oxygen above 2 mg/L.
The challenge
The two existing positive-displacement blowers were 14 years old, with no speed control. They ran flat-out 24/7 against a partially-closed throttle valve to match demand — wasting roughly 30% of their motor energy as throttling losses.
The solution
3× RB Series Roots blowers with VFD speed control:
- 2 active + 1 standby (lead/lag/standby rotation)
- VFD speed automatically tracks dissolved-oxygen sensor signal
- No more throttle valve — blowers slow down when demand drops at night
- Acoustic enclosures bring blower-house noise to 72 dB(A)
The result
- Energy use: ~32% lower vs. the old throttled-flat-out setup
- Annual energy saving: 410,000 kWh (about 1.85 M THB at current rates)
- DO setpoint stability ±0.1 mg/L vs. ±0.4 mg/L before — better treatment quality
- Standby unit means zero unplanned process downtime during maintenance
- ROI: 28 months on energy savings alone