Types & Functions of Aerators in Wastewater Treatment

When a wastewater treatment system (WWTP) is not equipped with a proper aeration mechanism, especially in the biological process - various problems may arise: bacteria fail to grow, foul odor increases, sludge settles, and the pollutant reduction process becomes slow. As a result, the discharge water quality may fail to meet environmental standards, increasing the risk of penalties or shutdown.

Why Aeration is Important in Biological Systems

Aeration is a key step in maintaining dissolved oxygen (DO) in wastewater treatment. Oxygen is required by aerobic bacteria to break down organic compounds and nutrients. Without adequate aeration, biological processes such as activated sludge, MBBR (Moving Bed Bio-Reactor), or aeration ponds will be disrupted. With optimal aeration, the system will:

• Increase the rate of organic degradation
• Prevent foul-smelling anaerobic conditions
• Ensure process stability during increasing wastewater loads

Mechanism of Supplying Oxygen to Bacteria

There are two main aeration methods used in the industry:

• Air diffusion: Air is injected into the basin through diffusers or perforated pipes, forming small bubbles that increase the oxygen-water contact surface area.
• Surface agitation: The water surface is stirred or splashed so oxygen dissolves faster into the wastewater.

The effectiveness of aeration is influenced by bubble size, basin depth, agitation speed, temperature, and wastewater characteristics (such as oil or surfactants that hinder oxygen transfer).

How to Calculate Air Requirements Based on Organic Load

In designing the right aerator, the key steps are:

• Determine the organic load (kg/day) to be treated.
• Calculate oxygen requirements: a rough estimation uses a factor of 1.1 × BOD (kg O₂/day).
• Adjust based on aerator technical data: Oxygen Transfer Rate (OTR), hourly capacity, and efficiency (α/β).
• Consider a safety margin for peak load or fluctuation conditions.
   

Simple example: If BOD = 500 kg/day → oxygen requirement is around 550 kg O₂/day → choose an aerator that can provide equivalent capacity + operational margin.

Case Studies on Aerator Usage

Hospital WWTP

• Problem: High ammonia levels (40-60 mg/L) requiring stable nitrification, but previous aeration was insufficient.
• Aerator Solution: Installation of a fine bubble diffuser with a larger capacity blower to meet nitrification O₂ demand.
• Result: Ammonia decreased from 50 mg/L → 1,500 mg/L and high oil content, causing fast oxygen depletion and foul-smelling aeration basin.
• Aerator Solution: Use of a coarse bubble aerator because it is more resistant to oil/grease and less prone to clogging.
• Result: DO stabilized at 2-3 mg/L, odor disappeared, and BOD removal efficiency increased.

Tips for Choosing the Right Aerator

• Oxygen Requirement (OTR): Choose an aerator capable of meeting total oxygen demand (BOD, nitrification, and respiration) according to aeration basin capacity.
• Biological Process Type: Aerator must match WWTP processes such as activated sludge, MBBR, SBR, or aerobic ponds.
• Wastewater Characteristics: Consider TSS, oil/grease, and organic load; harsher conditions are more suitable for coarse bubble or surface aerators.
• Aeration Basin Depth: Diffusers are more efficient in deep basins (>3 m), while surface aerators are ideal for shallow basins.
• Ease of Operation & Maintenance: Prioritize aerators that are easy to remove, resistant to clogging, and have spare parts readily available.
• Cost (CAPEX & OPEX): Adjust selection based on initial investment and long-term operating costs.

Common Mistakes in Aerator Installation

• Aerator selection does not match basin depth, causing low oxygen transfer efficiency.
• Aerators are not distributed evenly, resulting in dead zones and suboptimal mixing.
• Blower air flow does not match requirements, causing low DO or wasted energy.
• No check valve or pressure control installed, risking wastewater entering the blower or unbalanced air distribution.
• Poor maintenance access, making diffusers or aerators difficult to remove and prone to clogging without proper cleaning.

Aerators play a crucial role in ensuring wastewater treatment systems operate optimally. With proper selection based on wastewater characteristics and field conditions, biological processes become more efficient, stable, and compliant with regulations.

Need a Wastewater Treatment Solution? PJL enviro provides end-to-end solutions that can be customized for your industry needs.