WASTEWATER
By Rick Lallish
Solids retention time (SRT) is an important process control measure. What does it mean?
A. How long the flow remains in the system
B. How much time it takes for the stalk ciliates to populate
C. How long a suspended solids particle remains under aeration
D. How long the bacteria remain in the secondary clarifier
Answer: C. Process control and process control math are important measures that operators must understand to operate the plant efficiently. SRT (synonymous with MCRT) is one of these controls. SRT is the measurement of how long a suspended solids particle remains under aeration and is measured as age. This is the formula for SRT:
Pounds of suspended solids in system divided by pounds of suspended solids leaving the system, in days.
More information may be found in the CRC publications, Applied Math for Wastewater Plant Operators, Chapter 5.
DRINKING WATER
By Drew Hoelscher
How many disinfectant byproducts (DBPs) make up the total trihalomethanes (TTHMs)?
A. 2
B. 3
C. 4
D. 5
Answer: C. A total of four disinfectant byproducts can contribute to the calculation of the total trihalomethane concentration: bromodichloromethane (MCLG zero), bromoform (MCLG zero), dibromochloromethane (MCLG 0.06 mg/L), and chloroform (MCLG 0.07 mg/L). The TTHMs may be only a portion of the DBPs in tap water. Bromate, chlorite and haloacetic acids are also regulated by the National Primary Drinking Water Regulations.
About the authors
Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.
