How to Assess Aeration Tank Performance Using Protozoa & Metazoa

How to Assess Aeration Tank Performance by Observing Protozoa and Metazoa in Mixed Liquor

In Wastewater Treatment plant activated sludge systems, the operational status of aeration tanks directly affects effluent quality. Beyond conventional physicochemical testing, observing the species and quantities of protozoa and metazoa in mixed liquor provides an economical, rapid, and effective biological monitoring method. These microorganisms serve as "bioindicators," reflecting the operational status and treatment efficiency of aeration tanks.

The Indicator Role of Protozoa and Metazoa

Protozoa and metazoa are crucial components of the activated sludge ecosystem, occupying higher positions in the food chain and being highly sensitive to environmental changes. Different species of microfauna have varying adaptability to water quality conditions, making their population dynamics valuable indicators of system performance.

Common Indicator Organisms and Their Significance

Flagellates:

• Abundance typically indicates system start-up phase or excessive loading
• Suggests high organic matter concentration and insufficient dissolved oxygen

Sarcodina (e.g., Amoeba):

• Common during sludge cultivation phases or during sludge bulking
• Indicates system instability and high organic concentration

Free-swimming ciliates (e.g., Paramecium):

• Moderate numbers suggest system recovery
• Excessive numbers may indicate load fluctuations

Sessile ciliates (e.g., Vorticella, Epistylis):

• Numerous and active Vorticella indicate good system performance
• Epistylis dominance may suggest low loading conditions

Metazoa (e.g., Rotifers, Nematodes):

• Moderate rotifer populations indicate sludge maturity and effective treatment
• Excessive rotifers may suggest excessive sludge age
• Increased nematodes may indicate sludge aging or oxygen deficiency

Methods for Assessing Aeration Tank Performance

1. Relationship Between Biological Community and Treatment Efficiency

2. Observation of Biological Activity

Beyond species and quantity, organism activity should be noted:

Good activity: Active individuals with intact structures indicate suitable conditions

Poor activity: Sluggish movement, abnormal morphology (e.g., Vorticella without stalks, immobile cilia) may indicate toxic substances or DO deficiency

3. Population Trend Analysis

Gradual changes: Typically reflect normal parameter adjustments

Sudden changes: May indicate influent quality shocks or operational errors

Practical Recommendations

Sampling method: Collect mixed samples from different aeration tank locations, observe immediately (preferably within 30 minutes)

Observation frequency: Daily during normal operation, more frequent during upsets

Observation tools: Standard optical microscope (100-400× magnification) sufficient

Recording content: Species, quantity, activity, morphological characteristics

Important Considerations

Biological observations should complement physicochemical parameters (COD, DO, SV30, etc.)

Biological communities may vary between Treatment Plants - establish local baseline data

Seasonal variations affect biological populations - consider temperature factors

Through systematic long-term observation records, operators can develop site-specific microfauna databases, enabling more accurate prediction of system trends through microorganism changes and timely process adjustments to maintain stable treatment performance. This biological monitoring method, while seemingly simple, becomes a powerful operational management tool in experienced hands.

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