(1), MLSS (mixed liquid suspended solid)

Refers to the dry weight of suspended solids contained in the mixed liquor of 1L aeration tank, which is an index to measure the amount of activated sludge in the reactor. Including microbial thalli (Ma), microbial autoxidation products (Me), organic matter (Mi) and inorganic matter (Mii) adsorbed on sludge flocs and not degraded by microorganisms. Because MLSS is easy to determine, it is often used as an index to estimate the number of microorganisms in activated sludge in engineering. In engineering design, it is hoped to maintain a high MLSS to reduce the volume of aeration tank and save land occupation and investment, but the MLSS concentration should not be too high, otherwise it will lead to insufficient oxygen supply. In general, the sludge concentration in the reactor is controlled at 2000 ~ 6000 mg/L.

(2), MLVSS (mixed liquid volatile suspended solid)

Refers to the content of volatile suspended solids in the mixed liquor of 1L aeration tank, which only includes microbial thalli (Ma), microbial autoxidation products (Me), organic matter (Mi) adsorbed on sludge flocs that cannot be degraded by microorganisms, and excludes inorganic matter (Mii). Therefore, MLVSS can accurately reflect the number of microorganisms in the reactor. Generally speaking, the MLVSS/MLSS ratio of activated sludge treating domestic sewage is about 0.75, but it varies with the quality of industrial sewage, and the MLVSS/MLSS ratio is very different.

(3)、SV%

Sludge sedimentation ratio, the ratio of sludge volume to the original mixed liquid volume after the mixed liquid in the aeration tank stands still in the measuring cylinder for 30 minutes. Normal activated sludge can approach its maximum density after settling for 30 minutes, so SV% roughly reflects the amount of sludge in the reactor during normal operation and can be used to control sludge discharge. The normal value of SV% in general aeration tank is 20%~30%. The change of SV% can also reflect the abnormal situation such as sludge bulking in time. Therefore, SV% is an important index to control the operation of activated sludge process.

(4)、SVI

Sludge volume index refers to the volume of dry sludge 1g after the mixed liquor of aeration tank settles for 30 minutes, and the unit is ml/g. ..

SVI= = sludge volume/dry weight of sludge after settling for 30 minutes.

=(SV%× 100)/MLSS

SVI reflects the degree of looseness and cohesion of sludge. If the SVI is too low, it means that the sludge particles are fine and dense, with more inorganic substances and less microorganisms. At this time, the sludge lacks activity and adsorption capacity. Excessive SVI indicates that the sludge structure is loose, it is difficult to precipitate and separate, and it is about to expand or has expanded.

(5) Spatial data infrastructure

That is, the sludge density index refers to the grams of activated sludge contained in 100ml mixed solution after standing for 30min. 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 a lot of inorganic suspended solids, the sludge density is high and the SVI is low, but its activity and adsorption capacity are not necessarily poor, I hope it is useful to you. Activated sludge process is a treatment process that uses suspended activated sludge as the main body and uses the adsorption, coagulation and oxidative decomposition of activated sludge to purify organic matter in wastewater.

The equipment of activated sludge process consists of primary sedimentation tank, aeration tank, sedimentation tank, sludge reflux and excess sludge discharge system.

The wastewater from the primary sedimentation tank and the returned activated sludge enter the aeration tank together to form a mixed solution. The aeration tank is a bioreactor. Air is introduced through aeration equipment, and the oxygen in the air dissolves into the mixed solution, resulting in aerobic metabolic reaction. Aeration equipment not only makes oxygen pass into the mixed liquid, but also makes the mixed liquid fully stirred into a suspended state. In this way, organic matter, oxygen and microorganisms in wastewater can fully contact and react.

Then the mixed liquid flows into the sedimentation tank, the suspended matter in the mixed liquid precipitates in the sedimentation tank and is separated from the water, and the treated effluent flows out of the sedimentation tank. Most of the sludge in the sedimentation tank flows back, which is called reflux sludge. The purpose of sludge reflux is to maintain a certain concentration of suspended solids in the aeration tank, that is, to maintain a certain concentration of microorganisms. Biochemical reaction in aeration tank leads to the proliferation of microorganisms, which are usually discharged from sediments to ensure the stable operation of activated sludge system.

For more information, please visit Hubei Environmental Protection Industry Network.