The phenomenon of activated sludge aging is widely prevalent in most aerobic biochemical systems currently in operation. The aging of activated sludge not only leads to an increase in the main pollution indicators in the effluent but also results in significant energy waste. This is because the aging of activated sludge is often associated with excessive aeration and low loading, both of which consume excessive energy.

What is sludge aging?

Sludge aging is primarily caused by a prolonged lack of nutrients for microorganisms, resulting in an imbalance between nutrients and microbial quantity. Microorganisms cannot grow normally, but the actual operation of treatment facilities is more complex. The activity of sludge also depends on operational control conditions, nutrient ratios, and other factors. In some cases, even when the incoming water concentration is normal, if the carbon-nitrogen or carbon-phosphorus ratios are low, the sludge activity can be very poor, limiting the microorganisms' degradation of organic matter and reducing the generated energy. When both the incoming water concentration and nutrient ratios are normal, but excess sludge is not discharged as required, combined with excessive aeration time, the sludge can become loose and have poor activity, which is also commonly referred to as aging.

Analysis of Reasons for Sludge Aging

1The wastewater treatment system has been operating at a low load for an extended period.

In other words, the concentration of organic pollutants in the incoming water is too low, and it remains at this low level for an extended period. For instance, ...CODBelow100mg/LIn theory, if the incoming water concentration and flow rate are too low, simply reducing the activated sludge concentration should suffice. However, it is crucial not to overlook the fact that with excessively low incoming water concentration, the likelihood of collisions between activated sludge particles is diminished, ultimately leading to a failure in flocculation and settling.

2Over-oxidation leads to the aging of active sludge.

The reasons for this are explained at the beginning of the article. Excessive aeration leads to the disintegration of activated sludge and oxidation, with oxygen in the air acting as an oxidizing agent. Naturally, over-aeration results in the oxidation of some bacteria within the activated sludge, causing the floc to disintegrate.

3High sludge concentration

The activated sludge concentration is too high and lacks the support of a metal substrate concentration; in simpler terms, that is...C、N、PThe ratio between them is severely unreasonable and will eventually lead to the aging of the activated sludge.

4Not removing silt in a timely manner.

Sedimentation is a commonly used initial step in controlling the concentration of activated sludge. Delayed sedimentation can have a significant impact on sludge, and if sedimentation is not performed for a prolonged period, the activated sludge may...No Chinese content provided.Rapid aging occurs.

III. Judgment of Activated Sludge Aging

1The aged activated sludge is prone to disintegration, thus, the tiny bacteria can be found floating in the water. However, the water remains clear between the free bacteria. It doesn't result in the constant turbidity of wastewater. But in the late stage of aging, severe disintegration can lead to cloudy effluent!

2The aeration pond begins to produce a mixture of foam and floating scum, usually in a thin layer that does not accumulate, with a grayish-white color (determined by the system's color).

3The flocs become larger and the sludge color changes from light to yellow or appears very dark and gray-black, lacking vibrant luster.

4The foam generated from the returned secondary sedimentation tank sludge falls between surfactant and biological foam, feeling somewhat sticky.

5The sediment structure is loose, with fewer filaments and more rotifers, and fewer protozoa.

6The settling speed of aged activated sludge is slower than that of normal activated sludge.1.5No Chinese content provided.

Section 4: The Relationship Between Sludge Aging and Various Process Control Indicators

The relationship between various process indicators and the aging of activated sludge is quite close, and these relationships also help us confirm whether the activated sludge is aging and whether the correction of aging is accurate.

1No Chinese content provided.F/MThe relationship

F/MLow control is a significant cause of aging in activated sludge, which is also relatively easy to adjust. The extent of its aging is...F/MThe degree of lowliness is positively correlated.

2The relationship with dissolved oxygen

In relation to dissolved oxygen, besides the issue of excessive aeration leading to aging of the activated sludge due to overly high dissolved oxygen control, such problems become more pronounced under low food-to-microorganism ratios. Exceeding...4.0mg/LThe aeration should be classified as excessive waste aeration, as such aeration often leads to the aging of active sludge.

3Relationship with污泥龄

Maintain7-10The sludge age at Tian is within a reasonable range; for those exceeding...1Pay close attention to the sludge age phenomenon over a month; such sludge ages need to be controlled, as it inevitably leads to the aging of active sludge.

Method to Control Sludge Aging

1、 Requirements for controlling the activated sludge age

To ensure that the activated sludge in the biochemical system does not age due to untimely sludge removal, we must frequently confirm the relationship between the current sludge flow rate and the activated sludge concentration. By verifying the food-to-microbe ratio, we indirectly guide the control of the activated sludge sludge flow rate. At the same time, it is essential to maintain uniformity in the sludge flow rate, avoiding intermittent and excessively fluctuating sludge removal methods.

2Aeration Uniformity and Prevention of Over-aeration

Efficiently control the aeration volume to prevent over-aeration, and ensure the outlet of the aeration pond is...DOConcentration Control2.5mg/LJust right. It also reduces excessive aeration's electrical consumption, laying the groundwork for cost reduction in treatment.

3Avoid low-load operation status

To prevent the occurrence of low-load operation, thereby avoiding the aging of activated sludge. In addition to maximizing the concentration and biodegradability of the substrate in the influent.  Further efforts are being made to reduce the concentration of active sludge as much as possible to ensure that the F/M ratio remains within a reasonable controlled value.0.15-0.25In necessary cases, supplementary carbon sources can be added to ensure the normal operation and reproductive function of the activated sludge, such as adding septic tank water or introducing domestic wastewater.

4IncreaseMBRProcess

MBRProcess has replaced the secondary sedimentation tank, enabling...HRTPlease provide the Chinese content that needs to be translated into American English.SRTSeparation ensures long-term severe sludge aging without significantly affecting the effluent quality.