The reason for the generation of scum in the biochemical tank is due to abnormal metabolism from the activated sludge system, or it may be caused by the floating of inorganic particles.
Secondary sedimentation tank scum: scum from the biochemical system, sludge rising after nitrification of activated sludge in the secondary sedimentation tank, and anaerobic sludge rising due to severe hypoxia in the secondary sedimentation tank.
Cause of foam: the viscosity of the water body increases, mainly due to the high content of organic matter in the water body, the aging of activated sludge in the aeration mixture, the excessive detergent or surfactant in the influent, and the expansion of dead bacteria.
Type of foam
1. Brown yellow: the activated sludge is aged, and the sludge is disintegrated due to aging. It is suspended in the mixed solution and attached to the foam, leading to the extension of foam rupture time and the formation of scum.
2. Grey black: Activated sludge lacks oxygen and experiences local anaerobic reactions. Additionally, it is possible to analyze whether there are black inorganic substances present in the incoming water.
3. White: sticky and hard to break foam, bright white in color, good in accumulation, because the water inflow load is too high;
Sticky but easily broken, with an old white color and poor stacking ability, only locally accumulated due to excessive aeration;
4. Color: The incoming water is colored and has a high load; Water with detergent or surfactant.
Types of floating slag
1. Black thin liquid scum: Activated sludge lacks oxygen
2. Black and excessive accumulation of liquid surface scum: The sludge is severely lacking in oxygen or anaerobic conditions.
3. Brown and thin floating slag: normal without accumulation.
4. Brown and excessive accumulation of floating slag: nitrification reaction occurs inside the sludge; Severe filamentous bacterial expansion.
Foam scum combination analysis failure
1、 Brown yellow foam: it indicates that the activated sludge is in or will enter the sludge aging state.
1. Determine whether the sedimentation ratio is less than 8, whether the sludge color is dim, whether the sedimentation speed is too fast, and judge whether the sludge is aging when the foam color is brown.
2. In combination with SVI less than 40, it can be judged that the sludge is aged according to the brownish yellow foam.
3. In combination with microscopic examination, the microbial micelles are relatively dense, and metazoa appear in large numbers. According to the fact that the foam is brownish yellow, it can be judged that the sludge is aging.
2、 Gray black foam: it represents that the activated sludge system has anoxic or anaerobic status.
The key is to make a comprehensive judgment on dissolved oxygen. Uniformly distribute points on the pool body for dissolved oxygen measurement. If DO is less than 0.5mg/L, it needs to be confirmed with emphasis. Considering whether the regional sludge is thoroughly mixed and whether there is a sedimentation dead zone.
3、 White foam: it indicates that the activated sludge load is too high, aeration is excessive, and detergent enters.
1. F/M and white foam: if F/M is greater than 0.5, high load operation can be confirmed, and foam is normal at the initial stage of bacteria culture
2. DO and white foam: if DO is greater than 5.0mg/L, it means excessive aeration, which leads to sludge peroxidation and disintegration. Generally, it is sufficient to control DO not less than 2mg/L.
3. Issue with external substances: entry of detergents or surfactants. Detecting DO and sludge load can infer whether there are any incoming substances.
4、 Colored foam: It is related to the entering color, detergent and surfactant.
By observing whether the effluent from the physical and chemical treatment area has color, it can be determined whether colored water has entered; Observe whether there is foam generated by the hydraulic jump in the physicochemical zone to determine whether detergent enters.
5、 Black thin liquid surface floating slag: Control the DO value to determine whether there is a relative or local shortage of dissolved oxygen. A comprehensive measurement confirmation is required. For the discoloration caused by excessive oxygen deficiency in the wastewater itself, strengthening the reflux of wastewater can alleviate the occurrence of a large amount of floating slag.
6、 Excessive accumulation of black liquid surface scum: Microscopic examination did not reveal any active sludge protozoa. The sludge particles were dispersed without flocculation, and the settling performance was poor. The supernatant was turbid, and the color of the sludge sediment was dull and dark.
Reason: Insufficient dissolved oxygen, resulting in local anaerobic or hypoxic conditions.
7、 Brown thin liquid surface floating slag: Combined with the settling ratio, it was found that the supernatant was slightly turbid, containing disintegrated small particles. The interstitial water was clear, and the floating slag had viscosity and was not easy to stir and sink.
Reason: F/M is less than 0.05 and has a long duration.
8、 Excessive brown accumulation of floating slag on the liquid surface:
1. Related to filamentous bacteria; Combining microscopic examination with SVI or combining with SV to determine whether filamentous bacteria have expanded.
2. Related to denitrification of activated sludge: Combined with SV, it was found that small sludge flocs float upwards, accumulate on the liquid surface, and can quickly sink after stirring; When measuring C/N and determining whether the influent contains excessive N, in the case of insufficient carbon source, sludge is prone to denitrification, while ensuring that dissolved oxygen is greater than 3mg/L.
Prevention and control of scum and foam
1. The problem of self-control of sewage leads to:
A。 Failure to discharge sludge in a timely manner, excessive sludge age: appearing brownish yellow and thin; Control sludge aging; Confirmation can be made by combining F/M, SV, and mirror components.
B。 Low sludge concentration control and high load: confirm with microscopy and F/M. Check if there are any non activated sludge like organisms present and if the F/M ratio is greater than 0.5
C。 Failed to effectively control filamentous bacteria:
D。 Incorrect aeration method: excessive aeration.
E。 Relatively insufficient nutrient dosage:
Countermeasures for eliminating scum foam: spray with water.
