Aerated tank sludge aging judgment and solution!

Activated sludge aging is common in most aerobic biochemical systems, and the aging of activated sludge leads not only to an increase in the major pollution indicators of the effluent, but also to a waste of energy. Due to the aging of activated sludge, excessive aeration and low loads tend to cause excessive energy consumption.

1. Key points for judging the aging of activated sludge

(1) In the initial stage, when the sedimentation ratio is calculated, the supernatant becomes turbid, with fine sludge suspended and difficult to settle, and there will be scum and floating mud in the secondary settling tank.

(2) Sludge aging will lead to an increase in the oxygen consumption of the sludge in the aeration tank. Look out for signs of a sudden drop in dissolved oxygen.

(3) Microscopic examination shows that the sludge structure is loose, there are few filamentous bacteria, numerous rotifers, and few protozoa.

(4) During the reaction process, the sludge in the secondary sedimentation tank will generate a kind of air bubble between the biological and surface active substances, which has a certain viscosity.

(5) If the organic load rate (F/M) is overly low, the probability of activated sludge aging is elevated.

Organic load rate (F/M), also called sludge load. F refers to organic matter, M to microorganisms, and F/M is the amount of organic matter per unit weight of activated sludge per unit time, or the amount of organic matter removed per unit time by the effective volume of the biochemical pool. Activated sludge aging generally occurs, or may occur, when F/M is at or remains at a low level for a prolonged period of time, especially when F/M is below 0.05, with a extremely high probability of activated sludge aging.

2. Analysis of the cause of activated sludge aging.

(1) The sludge is not discharged in time, and the sludge age is too long

(2) The influence is in a low-load state for a long time and the activated sludge is aging

(3) Activated sludge caused by excessive aeration

The direct result of over-aeration is the disintegration and self-oxidation of activated sludge. The decomposition is due to the frequent shearing of the activated sludge, and the understanding of its own oxidation is that oxygen is its own oxidant, and that excessive aeration will cause it to oxidize.

(4) Activated sludge concentration control is too steep

The concentration of activated sludge is controlled to be overly elevated and there is not sufficient support for the concentration of the influent substrate, which will eventually lead to the aging of the activated sludge.

3. An effective method to suppress aging in activated sludge.

(1) Requirements for the control of activated sludge concentration

In order to ensure that the activated sludge will not age due to failure to discharge the sludge in time during the operation of the biochemical system, it is necessary to regularly determine the relationship between the current sludge discharge flow and the concentration of the activated sludge, so as to indirectly guide the sludge discharge flow of the activated sludge. At the same time, uniformity of sludge discharge flow must be achieved, and intermittent and excessive flow fluctuations of sludge discharge methods should be avoided.

(2) The uniformity of aeration and the prevention and control of excessive aeration

This is required to effectively control the volume of aeration, to avoid over-aeration, and to control the DO concentration to approximately 2.5 mg/L at the outlet of the aeration tank. At the same time, it can also reduce the electrical energy consumed by excessive aeration, setting the stage for lower treatment costs.

(3) Avoidance of low-load operating conditions

This is necessary to avoid the emergence of a low-load operation state and thus the occurrence of activated sludge aging. In addition to increasing the concentration and biodegradability of the substrate in the influent as greatly as possible, it is necessary to reduce the concentration of activated sludge as much as possible to ensure that the food-microbial ratio can be kept within a reasonable control value (about 0.15-0.25). If necessary, additional carbon sources can be added to ensure the normal operation and reproduction of activated sludge, such as the introduction of domestic sewage.

4. Performance of various process control metrics during activated sludge aging.

There is a close relationship between each process parameter and the aging of activated sludge, which also provides a basis for determining whether the aging of activated sludge is correct.

(1) Relationship with F/M

The low control of F/M is an essential reason for the aging of activated sludge. It should be mentioned that it is relatively easy to adjust. There is a positive correlation between the degree of aging and the low degree of F/M.

(2) Relationship with dissolved oxygen

In terms of the relation to dissolved oxygen, in addition to the aging of activated sludge due to excessive aeration and peak dissolved oxygen control, such problems become more prominent in the case of low food-to-microbial ratios. Aeration above 4.0 mg/L should be classified as excessive waste aeration, and it is more common for the results of such aeration to contribute to the aging of activated sludge.

(3) Relationship with sludge age

Maintaining a sludge age of 7-10 days is a reasonable range. Special attention should be paid to the phenomenon of sludge age exceeding 1 month. Such sludge age should be controlled, which will inevitably cause activated sludge to age.