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Common problems of sludge treatment- Determination of sludge age

Source:Jiangsu Envset     Time:27 October 2020

Sludge age

Sludge age is an important parameter for the design and operation of activated sludge treatment system. It can explain the status of activated sludge microorganisms. Microbes with a generation time longer than sludge age cannot multiply into dominant species in the aeration tank. Below we briefly introduce the definition and determination of sludge age.


Sludge age (Sludge Retention Time) refers to the average residence time of microorganisms in the reaction system from their generation to the discharge of the system, that is, the time required for all the microorganisms in the reaction system to be updated once.

Sludge age (t)=VX1/24X2Q
     In the formula: V—aeration tank volume m;
     X1—Mixed suspended solids (MLSS) concentration in aeration tank (mg/L);
     X2—Mixed suspended solids (MLSS) concentration (mg/L) of returned activated sludge;
     Q—Remaining activated sludge displacement (m3/h)

The sludge age can be understood as the time required for the activated sludge to proliferate twice. In actual operation, the sludge age can be simply estimated based on the sludge volume and discharge flow of the aeration tank. The range of sludge age from 7 to 15 days is just a reference value. In actual operation, a reasonable sludge age should be set according to the on-site water load.

How to determine the age of sludge during operation?

Under the premise of "how many microorganisms can be supported by as much food", during operation, it is necessary to calculate the reasonable sludge concentration (MLSS) based on the average pollutant load over a period of time using the food micro-ratio formula, and then calculate the reasonable sludge age , And make corresponding adjustments to the system based on this.

Jiangsu Envset provides customers with high-quality sludge treatment equipment. We have professional wastewater treatment equipment manufacturing technology and experienced employees. If you have any questions about determining the age of sludge, please contact us.

Tag: sludge age determination, sludge age definition, Sludge Retention Time