Exam Study Guide: Activated Sludge Math

Exam Study Guide: Activated Sludge Math

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When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to properly study and prepare for exam questions. Take a look at this sample wastewater treatment licensing question along with an explanation of the correct answer.

Sample question:

What is the sludge volume index of a plant given the following information:

  • MLSS 3250 mg/L                     
  • RMLSS 4250 mg/L                    
  • Settleometer: 5-minute reading, 950; 15-minutes reading, 780; 30-minute reading, 540;  

A) 127
B) 166
C) 183
D) 240


SVI is calculated by taking the 30-minute reading from a settleometer test and dividing it by the MLSS (or RAS MLSS for RAS SVI) and multiplying the resulting number by 1,000. This test gives the operator a determination for settling characteristics of sludge in secondary clarifiers. The test should be conducted over a period of time to set a baseline for each plant's unique characteristics. The answer is therefore, B.

Source: ERTC Math Text book/WEF MOP11 20-103

About the author
Ricky Lallish is the water pollution control program director at the Environmental Resources Training Center of Southern Illinois University Edwardsville. He provides training for entry level operators in the wastewater field and operators throughout the state looking to further their education.


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