Key Considerations When Selecting Air Blowers for the Activated Sludge Process

In wastewater treatment, the activated sludge process is widely used for its effectiveness in removing organic pollutants. A critical component of this process is the air blower system, which provides the oxygen necessary for aerobic bacteria to break down organic matter. The right air blower not only supports optimal biological activity but also significantly affects the plant’s energy consumption and operational costs. Here are key factors to consider when selecting air blowers for an activated sludge process.

1. Air Demand and Process Requirements

The first and most important step is determining the oxygen demand of the system. This depends on:

• Influent characteristics (Biochemical Oxygen Demand - BOD, flow rate)

• Biomass concentration

• Effluent quality targets

• Temperature

Air blowers must supply enough oxygen to meet the peak biological oxygen demand while maintaining appropriate dissolved oxygen (DO) levels, typically 1.5–2.5 mg/L in the aeration tank. Undersized blowers can cause under-aeration, affecting treatment performance, while oversized units may lead to wasted energy.

2. Blower Type and Efficiency

Common types of blowers include:

• Lobe (Roots) Blowers: Simple and durable, best for low-pressure applications, but less efficient.

• Centrifugal Blowers: Suitable for large flows with higher efficiency, but typically have a narrower operational range.

• Screw Blowers: Offer higher efficiency and variable speed, making them suitable for fluctuating loads.

• Turbo Blowers (High-Speed or Magnetic Bearing): Highly efficient and compact, ideal for applications where energy efficiency is paramount.

The right type will depend on your plant’s capacity, load variability, and lifecycle cost considerations. High-efficiency models may have a higher upfront cost but offer lower energy and maintenance costs over time.

3. Control and Modulation Capability

Activated sludge systems often experience variable load conditions throughout the day or season. The blower system should be capable of modulating air supply in response to real-time demand. Options include:

• Variable Frequency Drives (VFDs)

• Flow and pressure sensors

• DO-based automatic control systems

A well-integrated control system helps maintain consistent treatment performance while optimizing energy use, which is typically the largest operational cost in biological treatment.

4. System Pressure Requirements

The blower must overcome all system head losses, including:

• Diffuser head loss

• Pipe friction

• Static head

Ensure the blower is selected to provide enough pressure under worst-case scenarios, without operating too far off its efficiency curve under normal conditions. Pressure requirements for fine-bubble diffusers are typically higher than for coarse-bubble systems.

5. Reliability and Maintenance

Blowers are a critical asset—downtime can severely impact treatment. Look for:

• Proven technology and track record

• Manufacturer support and local service availability

• Maintenance intervals and ease of access

• Spare parts availability

Systems with oil-free air delivery (e.g., magnetic-bearing turbo blowers) can reduce maintenance requirements and potential contamination risks.

6. Noise and Footprint

Especially for plants located near residential or commercial areas, noise level is a key concern. Blower selection should consider:

• Manufacturer-rated noise output

• Enclosure options

• Space availability for installation and future expansion

Some high-efficiency blower types, such as turbo blowers, have much smaller footprints and lower noise levels.

7. Lifecycle Cost Analysis

Beyond purchase price, consider:

• Energy consumption (kWh/kg of BOD removed)

• Maintenance and spare parts

• Downtime risks

• Operational flexibility

A full lifecycle cost analysis will often justify investment in higher-efficiency or more advanced blower systems.

Final Thoughts

Selecting the right blower for the activated sludge process requires a careful balance of technical, operational, and economic considerations. Collaboration between process engineers, equipment suppliers, and plant operators is crucial to ensure that the system delivers reliable performance, energy efficiency, and long-term value.

Properly selected and maintained, your blower system will play a vital role in the consistent and compliant operation of your wastewater treatment facility.