There are green microorganisms on the surface of the secondary sedimentation tank. What’s going on and how should it be dealt with?

Reasons for the appearance of excessive foam in the aerobic tank: 1. High levels of surfactants in the water (resulting from substances added during production; the foam is white, with small bubbles that are light in weight and non-sticky). 2. The proliferation of microorganisms produces large amounts of lipids or these microorganisms themselves (as a result of their growth and reproduction; the foam is muddy in color, with larger bubbles that are sticky). 3. Foam caused by the degradation of sludge (the foam that forms when aerobic sludge stays in the secondary sedimentation tank for too long becomes sticky and has a muddy color). The presence of green algae is definitely related to high levels of nitrogen and phosphorus; in addition, high dissolved oxygen levels can also lead to the growth of green algae. In some secondary sedimentation tanks, the dissolved oxygen concentration is even higher than that in the aerobic reaction tanks. Green algae can also appear when the secondary sedimentation tank is not used for a long time or when there is limited water inflow, resulting in a longer hydraulic retention time. The appearance of fine sludge in the secondary sedimentation tank can be attributed to: ① An insufficient sludge load in the aerobic tank, along with excessive aeration, which leads to the oxidation of the sludge and reduces its flocculation ability, causing the sludge structure to become dispersed (resulting in turbid water with many suspended particles). ② An excessive sludge load in the aerobic tank, coupled with insufficient dissolved oxygen, which reduces the sludge’s adsorption capacity and prevents complete decomposition of organic matter. ③The secondary sedimentation tank is overloaded, or uneven water distribution in the tank leads to gravitational flow; fast local flow velocities then lift up the sludge. ④The return ratio in the secondary sedimentation tank is too high, the sludge layer in the secondary sedimentation tank is too low, or the water flow disturbs the sludge layer excessively (this cause is less common). ⑤Excessive sludge discharge from the aerobic tank results in a too short sludge age there; as a result, the newly formed sludge flocs have difficulty settling (the water is clear but contains a high amount of suspended solids). ⑥The sludge in the aerobic tank is too long, and the sludge has aged. ⑦The sludge in the aerobic tank lacks nutrients, or the nutrient ratio is uneven (excessively high N:P ratio). ⑧Sludge bulking occurs in the aerobic tank, resulting in poor sedimentation properties; the sludge layer in the secondary sedimentation tank becomes thick, and the water flow carries away the sludge (this situation arises when either the SVI value is too high or too low). ⑨The nitrogen content in the wastewater from the aerobic tank is too high

The analysis on the second floor is very comprehensive; it’s necessary to compare it in order to identify the causes. It should be noted that, until the green algae in the secondary sedimentation tank are completely eradicated, it is necessary to remove them promptly to prevent them from clogging pipelines downstream!

An imbalance in the ratio of nitrogen to phosphorus is one of the causes.

Hello, I would like to ask: regarding the second reason for excessive foam in the aerobic tank, is it normal for a large amount of mud-colored foam to appear as a result of the microorganisms reproducing? In our company’s water treatment processes, when sludge bulking or sludge aging occurs, the foam also has a muddy color and consists of large, sticky bubbles.

It is likely caused by filamental fungi; this phenomenon can occur sometimes due to seasonal changes. Increase sludge removal, and if the impact is significant, use pressurized water to flush it away and break it up!

Is it normal too for the filamentous fungi to produce muddy-colored foam as a result of expansion or aging?