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TIPS for Biological Treatment without Testing Instruments
For a small wastewater treatment plant without testing instruments, how to judge the health of cultivated bacteria based on water color, sediment, and touch?
Without instruments, sensory methods (look, smell, touch) are common on-site empirical techniques to assess activated sludge (bacteria culture) health. Although not as precise as data, they allow quick identification of problem trends.
The logic below uses color, sediment, and touch and applies to aerobic activated sludge processes (e.g., AO, SBR, etc.).
1. Color: The most intuitive health indicator
Under normal conditions, healthy bacteria (activated sludge) appear tea-brown or earth-brown with an earthy, musty smell (not foul).
|
Color |
Possible Cause |
Judgement |
|
Yellow-brown / Earth-brown |
Good bacterial activity, adequate DO |
Good |
|
Dark brown / Black |
Low DO (hypoxia), or sludge decay |
Bad |
|
Gray-white / Pale yellow |
Excess DO, or very low organic load (sludge self-oxidation) |
Bad |
|
Greenish |
Algae bloom (usually sunlight exposure, long retention) |
Fair (may affect effluent SS but not necessarily bacteria) |
Key point: Look at the color of the mixed liquor in the aeration tank. If black → increase aeration immediately. If pale → reduce aeration or increase influent load.
2. Sediment: Use a beaker or clear bottle for a 30‑minute settling test
No instrument? Take a 2‑liter transparent plastic bottle or beaker of mixed liquor from the aeration tank and let it settle for 30 minutes.
2.1 Settling speed and sludge interface
2.2 Supernatant condition
2.3 Floc morphology (observe with naked eye or phone magnifier)
3. Touch: Feel the sludge texture with fingers
Take a small amount of settled sludge from the bottom and gently rub it between fingers (wear gloves or wash hands thoroughly afterward).
⚠️ Note: Smell your fingers after touching – healthy sludge smells like earth. Foul or rotten egg smell indicates anaerobic sludge decay.
4. Auxiliary judgement: Smell
5. If you have no instruments, build these three habits
Quick reference table
|
Sensory observation |
Judgement |
Action |
|
Brown colour, settles well, gritty/loose feel |
✅ Good bacteria |
Maintain current operation |
|
Black colour, foul smell, turbid supernatant |
❌ Low DO or decay |
Increase aeration, waste some sludge |
|
Pale/white colour, very slow settling, clear supernatant |
❌ Sludge bulking |
Check for filaments; add a little chlorine (if allowed) or raise DO |
|
Earth-brown but many fine flocs in supernatant |
❌ Over‑aged sludge |
Waste more sludge (reduce SRT) |
|
Earth-brown but supernatant muddy / turbid |
❌ Overload (high F/M) |
Reduce influent flow or increase aeration |
Final note: Sensory methods can tell you "good vs bad", but they cannot give precise quantities. If your budget is extremely limited, at least buy a portable dissolved oxygen meter (a few hundred yuan) and a graduated cylinder – they will greatly improve accuracy. The most common risks during bacteria cultivation are prolonged hypoxia or excessive aeration, which are hard to detect perfectly by eye and hand alone.
Hinada is the leading manufacturer of WWTP Equipments and Solutions provider, further inquiry or questions please contact with us.