Common Aerotank tank problems and how to fix them

Aerotank incidents during the operation of the WWTP often arise equipment problems such as pumps, aerators, valves and treatment process problems such as floating sludge, black sludge, dead sludge that generates bad odors, …

In fact, if the equipment maintenance regime is guaranteed and daily monitoring of basic parameters is carried out to ensure the operating conditions of the wastewater treatment system, the equipment’s lifespan can be extended. , construction items and limit incidents. However, in the event of an incident, determining the causes of the incident is important to support the timely implementation of response solutions. The causes corresponding to common problems and remedies are presented below:

Suspended activated sludge incident in Aerotank tank

Symptom 1: The sludge layer flows out in the waste stream, no sludge remains.

Due to overload of organic matter. Solution: Reduce organic load.
Due to low pH. Solution: add alkalinity.
Due to the growth of filamentous fungi. Solution: add nutrients, add chlorine or peroxide to circulate.
Due to nutritional deficiency. Fix: add nutrition.
Due to toxicity. Fix: Identify source, add preprocessing.
Due to excessive ventilation. Solution: reduce ventilation during low flow periods.

Symptom 2: A large amount of small solid particles leave the settling tank.

Cause: old sludge: reduces sludge age, increases waste flow speed.
Excessive chaos. Fix: reduce turbulence (low flow air blow control).

Symptom 3: large amounts of small, translucent particles leave the settling tank.

Due to the growth rate of sludge. Solution: increase sludge age.
Because the activated sludge is new and weak. Solution: reduce wastewater.

Symptom 4: The sludge settles well but floats to the surface in a short time.

Due to denitrification. Solution: increase circulation speed, adjust sludge age to limit denitrification.
Due to excessive ventilation. Solution: reduce ventilation.

Symptom 5: Microorganisms in activated sludge die in a short time.

Because the input stream contains toxic substances. Solution: separate activated sludge (if possible). Recirculate all solids present. Stop providing wastewater. Increase circulation speed. Add preprocessing programs.

Symptom 6: The surface of the aerobic tank is covered with a thick, greasy layer of foam.

Because the mud is too old. Solution: reduce sludge age. Increase wastewater volume, use foam control pumps.
Due to too much oil and fat in the system. Fix: enhance fat removal. Use foam control pumps. Add preprocessing programs.
Due to scum bacteria creating foam. Solution: remove these bacteria.

Symptom 7: Large clouds of foam appear on the surface of the aerobic tank.

Because the activated sludge is young, the amount of sludge is small. Solution: increase sludge age, reduce wastewater supply, use foam control pumps.
Due to detergents. Solution: limit surfactants, use foam control pumps.

Incidents related to Aerotank biomass

TT	PHENOMENA	CAUSE	THINGS TO BE CHECKED	SOLUTION TO REMEDY
1	On the surface of the Aeroten tank appear clusters of white foam that are difficult to dissolve or soap-like foam.	-Activated sludge is young (Low MLSS content), which also means the Aeroten tank is overloaded. This phenomenon is often encountered during the start-up phase of the Aeroten tank or restarting after the tank has a sludge death problem. This phenomenon will go away when the boot process ends.	– Check the Aeroten tank load (F/M), COD and BOD content in the input wastewater and the amount of MLSS in the Aeroten tank. – Check DO in Aeroten tank. – Consider seed sludge put into culture: quality and quantity.	– When recalculating the actual F/M value, we will see that this value is higher than the design value, so it is necessary to reduce sludge discharge and reduce the organic load introduced to the system. until the amount of sludge in the Aeroten tank develops well. – Enhance sludge circulation at a high level, limit sludge loss at output. Some cationic polymers can be used in the settling tank to increase sludge settling capacity and reduce sludge drift. – Maintain DO around 1-2 mg/l. – Seed sludge must be healthy sludge taken from treatment systems with similar properties. Using biological products helps shorten system startup time.
2		Excessive sludge discharge is the cause of overload in the Aeroten tank. Unfavorable conditions for biological treatment include: – Input wastewater contains highly toxic ingredients (heavy metals, biocides, antiseptics, etc.); – Nutrient deficiencies; – Water with high salt content; – pH fluctuates in a large range; – Low DO, low temperature. A sudden decrease in the amount of activated sludge in the Aeroten tank will overload the Aeroten tank.	Check and monitor whether the following issues occur: – MLSS content is reduced; – Sludge retention time is reduced; – F/M value increases; – Poor ventilation effect, reduced DO; – Sludge flow increases. Check the quality of input/output wastewater: about toxins, heavy metals, pH, salt content, temperature. Check the amount of solids in water after treatment. Check whether the mud is clumpy, floating or not? Check and record sudden changes in wastewater temperature.	Reduce sludge flow to no more than 10% for 1 day, until the system returns to normal operation. Enhance sludge circulation at a high level, limit sludge loss at output. If the cause is due to toxicity, it is necessary to perform a new culture of activated sludge in a toxic environment. Toxic sludge can be recycled back into the treatment process. It is necessary to check and take measures to control waste sources. The pH in the Aeroten tank can be low due to the nitrification process. At this time, it is necessary to add alkalinity (NaOH) to maintain the pH in the Aeroten tank in the range of 6.5-7.5.
3	Shiny, dark brown foam appears on the Aeroten tank	Aeroten tank is operating under load (low F/M) due to low sludge volume	Check and monitor whether the following issues occur: – MLSS content increases; – Sludge retention time increases; – F/M value decreases; – Poor ventilation effect, reduced DO; – Low sludge flow; – Temperature increases.	Increase the sludge flow but not greater than 10% in 1 day, until the system operates normally again and light brown foam appears on the surface of the Aeroten tank.</ td>
4	A thick layer of scum and dark brown foam appears on the Aeroten tank	Aeroten tank load is too low due to improper sludge disposal process.	Check and monitor whether the following issues occur: – MLSS content increases; – Sludge retention time increases; – F/M value decreases; – Poor ventilation effect, reduced DO; – Low sludge flow; – Increase NO3 content in output wastewater (>1 mg/l).	Increase the sludge flow but not greater than 10% in 1 day, until the system operates normally again and light brown foam appears on the surface of the Aeroten tank.</ td>
5	A thick layer of scum and dark brown foam appears on the Aeroten tank (continued)	Grease scum enters the Aeroten tank	Check oil and grease content in input wastewater. Check the grease removal efficiency of previous physicochemical treatment works	Check and control waste sources according to set parameters next. Consider adjusting the operations of physical and chemical treatment works.
6	Dark brown foam appears on the Aeroten tank, like grease and is very difficult to dissolve, possibly even in the output wastewater	Filamentous bacteria exist	Check and re-identify the types of bacteria in the Aeroten tank.	Controls the quality of incoming water and the circulation of fats and lipids. Reduce sludge retention time to 2-9 days, collect foam on the drainage tank and foam on the sedimentation tank.
7	Appears on the Aeroten tank, dark brown foam and mostly black foam like soap bubbles. The wastewater in the Aeroten tank is dark brown and black and has a foul smell	The Aeroten tank is operating in anoxic conditions.	Check DO again. Check the air blower and air distribution system. Check MLSS again.	Increase the aeration process and maintain DO in the Aeroten tank between 1-2 mg/l. Check if there are blockages, leaks or damage on the ventilation system, then clean, repair, or replace these parts. If MLSS is too high, increase sludge disposal to the appropriate F/M value.

Refer to how to calculate Aerotank tanks and tanks in the wastewater treatment system here

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