What are the performance indexes of activated sludge?

Performance indicators of activated sludge include: mixed liquor suspended solids (MLSS), sludge sedimentation ratio (SV), sludge index (sludge volume index (SVI), sludge density index (SDI).

1, mixed liquor suspended solids (MLSS), also known as sludge concentration of mixed liquor, represents the total weight of activated sludge solids contained in mixed liquor per unit volume of aeration tank, that is, MLSS=Ma+Me+Mi+Mii.

Ma-microbial population with metabolic function activity;

Me-the residue of endogenous metabolism and self-oxidation of microorganisms (mainly bacteria);

Weak inert organic matter that is difficult to be degraded by bacteria carried by raw sewage;

Inorganic substances carried by sewage.

The unit is mg/L mixed solution, or g/L mixed solution, g/m3 mixed solution and kg/m3 mixed solution.

Mixed liquor volatile suspended solids (MLVSS) indicates the concentration of organic solids in mixed liquor activated sludge, that is

MLVSS = horse+me+meter

The ratio of MLVSS to MLSS is expressed as f, that is

f=MLVSS/MLSS

In general, the F value is relatively fixed, and for domestic sewage, the F value is about 0.75. The same is true of urban sewage with domestic sewage as the main body.

The above two indicators can not accurately represent the microbial biomass of activated sludge, but the relative value of activated sludge. However, because of its simple determination, it is widely used in the design and operation of activated sludge treatment system.

2. Sludge sedimentation rate (SV), also known as 30min sedimentation rate. The volume of precipitated sludge formed after the mixed liquid is left standing in a measuring cylinder for 30 minutes accounts for the percentage of the original mixed liquid volume, expressed as%.

3. Sludge Volume Index (SVI), referred to as sludge index for short, its physical meaning is the volume of sludge deposited per gram of dry sludge after the mixed liquor at the outlet of aeration tank is left standing for 30min, and the unit is milliliter (mL).

The calculation formula of sludge volume index is:

SVI= activated sludge volume (ml) formed by static sedimentation of mixed liquor (1L) for 30 minutes/dry weight of suspended solids in mixed liquor (1L) (g)

=(SV (mL/L)) /(MLSS (g/L))

SVI is expressed in mL/g, and it is customary to call it only a number and omit the unit.

4. The sludge density index (SDI) refers to the grams of activated sludge contained in 100ml mixed solution after standing for 30 minutes. The unit is gram/ml.

Generally speaking, svi

100 & lt； The sludge settling performance of SVI<200 is average.

200 & ltSVI sludge has poor settling performance.

The water quality of urban domestic sewage is relatively stable, and its SVI is controlled at about 50~ 150. However, the quality of industrial sewage varies greatly. For example, COD in some industrial sewage is mainly dissolved organic matter, which is easy to synthesize sludge. Sludge contains less ash and more microorganisms, so although its SVI is high, it is not really sludge bulking. On the other hand, if the sewage contains more inorganic suspended solids, the sludge density is high and the SVI is low, but its activity and adsorption capacity are not necessarily poor.