AWWA AWWA Water Treatment Processes 2 — Questions and Answers
Question 1: What is the maximum contaminant level (MCL) for total trihalomethanes (TTHMs) in US drinking water under the Stage 2 Disinfectants and Disinfection Byproducts Rule?
- 10 µg/L
- 40 µg/L
- 80 µg/L (Correct answer)
- 100 µg/L
Correct answer: 80 µg/L
The Stage 2 D/DBP Rule sets the MCL for TTHMs at 80 µg/L, enforced using locational running annual averages at distribution system monitoring sites.
Question 2: What treatment process does AWWA recommend for removing taste and odor compounds such as geosmin and MIB from drinking water?
- Lime softening
- Activated carbon adsorption (Correct answer)
- Ion exchange
- Reverse osmosis only
Correct answer: Activated carbon adsorption
Powdered or granular activated carbon (PAC/GAC) is the AWWA-recommended treatment for adsorbing geosmin and 2-methylisoborneol (MIB) taste and odor compounds.
Question 3: In membrane filtration, which process has the smallest pore size and can remove dissolved salts and minerals?
- Microfiltration (MF)
- Ultrafiltration (UF)
- Nanofiltration (NF)
- Reverse osmosis (RO) (Correct answer)
Correct answer: Reverse osmosis (RO)
Reverse osmosis operates at the smallest pore scale (< 0.001 µm) and uses high pressure to remove dissolved salts, minerals, and most contaminants.
Question 4: What is the primary purpose of adding fluoride to drinking water per AWWA and US public health policy?
- To improve coagulation efficiency
- To prevent dental caries (tooth decay) (Correct answer)
- To control biological regrowth in distribution
- To adjust alkalinity for corrosion control
Correct answer: To prevent dental caries (tooth decay)
Community water fluoridation at 0.7 mg/L (the current USPHS recommendation) is practiced to reduce dental caries prevalence in the population.
Question 5: Which oxidant is commonly used in water treatment to convert soluble iron (Fe²⁺) and manganese (Mn²⁺) to insoluble forms that can be filtered?
- Sulfuric acid
- Potassium permanganate (Correct answer)
- Sodium bisulfite
- Hydrofluosilicic acid
Correct answer: Potassium permanganate
Potassium permanganate oxidizes soluble ferrous iron and manganous manganese to their insoluble precipitate forms, enabling removal by filtration.
Question 6: What is the significance of the 'jar test' procedure in water treatment plant operations?
- It tests for biological contamination in source water
- It determines the optimal coagulant type and dose for current raw water conditions (Correct answer)
- It measures filter run length before backwashing
- It evaluates disinfection byproduct formation potential
Correct answer: It determines the optimal coagulant type and dose for current raw water conditions
The jar test simulates coagulation-flocculation-sedimentation in a laboratory setting to identify the optimal coagulant and dosage for current raw water quality.
AWWA AWWA Water Treatment Processes 2
What is the maximum contaminant level (MCL) for total trihalomethanes (TTHMs) in US drinking water under the Stage 2 Disinfectants and Disinfection Byproducts Rule?