How To Adjust The Aeration Intensity Of A Wastewater Aeration Tank

1. Equipment Status Check

Check the blower's operating parameters (air pressure, airflow, and current) to ensure there is no abnormal noise or malfunction. Observe the aeration uniformity of the disc diffusers and check for blockages or damage, which may appear as localized absence of bubbles or uneven bubble distribution. Calibrate the DO online monitoring instrument using a standard solution (calibration error ≤ ±0.2 mg/L) to avoid measurement deviations.

2. Water Quality Data Collection and Recording

Collect and record key water quality data, including influent COD, BOD, and MLSS concentrations (average values over the past hour). Measure and record the DO value (current actual value), water temperature, and pH at both the inlet and outlet of the aeration tank.

3. Determining Adjustment Targets

Define the target DO based on the process type. Reference values include:

Conventional activated sludge process: 2.0–3.0 mg/L

Nitrification stage: 2.5–3.5 mg/L

Denitrification stage: ≤0.5 mg/L

Calculate the DO deviation using the formula:

DO deviation = Target DO − Current DO

A positive value indicates that aeration should be increased, while a negative value indicates that aeration should be reduced.

Step 1: Initial Adjustment of Aeration Intensity (Based on DO Deviation)

Adjustment Methods

Variable Frequency Blower

Adjust the blower frequency to change the airflow. Typically, each 1 Hz increase or decrease in frequency changes the airflow by approximately 5–8%.

Fixed Frequency Blower

Control airflow by opening or closing aeration valves in different zones of the aeration tank or by adjusting the valve opening.

Adjustment Range

DO deviation ≤ 0.5 mg/L:
Small adjustment (frequency ±1 Hz or valve opening ±10%)

DO deviation 0.5–1.0 mg/L:
Medium adjustment (frequency ±2 Hz or valve opening ±20%)

DO deviation > 1.0 mg/L:
Stepwise adjustment. First reduce the deviation to within 0.5 mg/L, stabilize for 1 hour, and then perform fine adjustments.

Reminder:
After each adjustment, allow the system to stabilize for 1 hour before rechecking the DO value. Avoid frequent large adjustments that may cause sudden fluctuations in DO.

Step 2: Observe Aeration Uniformity

After the second fine adjustment, measure the DO value every 5 meters along the length of the aeration tank to ensure that the DO deviation within the tank is ≤0.3 mg/L.

If localized low DO is observed (for example, DO at the tank outlet is below the target value):

Check whether the aerators in that area are clogged.

Appropriately increase the opening of the aeration valve in that zone.

If localized high DO is observed (for example, DO at the tank inlet > 4.0 mg/L):

Reduce the aeration intensity in that zone to prevent localized over-aeration.

Step 3: Dynamic Optimization Based on Water Quality Load

Adjust aeration dynamically according to influent water quality conditions.

Sudden Increase in COD/BOD (>120% of the design value)

Increase DO by 0.3–0.5 mg/L above the target value, and extend the aeration time (or temporarily reduce the influent flow rate).

Low Influent Load (<80% of the design value)

Reduce aeration intensity and maintain DO near the lower limit of the recommended range (e.g., 2.0 mg/L for conventional processes) to prevent sludge aging.

Excessively High MLSS (>4000 mg/L)

Appropriately increase aeration intensity (+0.5 mg/L DO) to ensure sufficient oxygen supply for microorganisms.

Step 4: Recording and Documentation

Establish an adjustment log that records:

Adjustment time

Blower parameters (frequency and airflow)

DO values before and after adjustment

Water quality data

Also record the reason for the adjustment (e.g., increased influent load or low DO) and the resulting effect (e.g., DO stabilized at 2.8 mg/L after adjustment).