What is the maximum turbidity level allowed in treated drinking water for effective disinfection?

0.3 NTU

True or False: Hypochlorous acid (HOCl) is less effective than hypochlorite ion (OCl⁻) for disinfection.

False. HOCl is 80-100 times more effective than OCl⁻ for disinfection.

The process of destabilizing colloidal particles using chemicals like alum is called _____.

Coagulation

What does TDS measure in water quality?
A) Total dissolved solids
B) Total dynamic substances
C) Thermal distribution system
D) Treatment dosage standard

A) Total dissolved solids

Why does water hardness primarily occur?

Due to calcium and magnesium ions in water

What is the typical velocity gradient (G) range for rapid mix basins?

700 to 1000 s⁻¹

True or False: Flocculation requires higher velocity gradients than rapid mixing.

False. Flocculation uses lower G values (20-75 s⁻¹) for gentle mixing.

The overflow rate in sedimentation equals the _____ of completely removed particles.

Settling velocity

Which membrane type removes dissolved salts and nearly all contaminants?
A) Microfiltration
B) Ultrafiltration
C) Nanofiltration
D) Reverse osmosis

D) Reverse osmosis

What happens when chlorine dose exceeds the breakpoint in water treatment?

Free chlorine residual begins to appear as combined chlorine is oxidized

The Camp-Stein equation Gt typically ranges from _____ to _____ for flocculation.

10⁴ to 10⁵

True or False: Noncarbonate hardness can be removed using lime alone without soda ash.

False. Noncarbonate hardness requires soda ash (Na₂CO₃) to provide carbonate ions.

What is the formula for calculating overflow rate in sedimentation basins?

V₀ = Q/As (flow rate divided by surface area)

Which disinfection method uses 254 nm wavelength light?
A) Chlorination
B) Ozonation
C) UV disinfection
D) Chloramination

C) UV disinfection

What does CT represent in disinfection calculations?

Disinfectant concentration multiplied by contact time

The effective size range for rapid sand filter media is _____ mm.

0.45 to 0.55

True or False: Increasing water temperature decreases disinfection effectiveness requiring higher CT values.

False. Higher temperature increases effectiveness, reducing required CT values.

Ion exchange removes dissolved ions by replacing them with _____ ions.

Resin-bound

A water plant treating 5 MGD needs 3 mg/L chlorine dose. What is the daily chlorine requirement?
A) 125 lb/day
B) 150 lb/day
C) 175 lb/day
D) 200 lb/day

A) 125 lb/day (5 × 3 × 8.34 = 125)

What causes alkalinity in water and how is it expressed?

Buffering capacity of water, expressed as mg/L as CaCO₃

The minimum pH required for magnesium removal in lime softening is _____.

11

True or False: Reverse osmosis typically achieves higher flux rates than microfiltration.

False. RO has lower flux (8-20 gfd) compared to MF (40-100 gfd).

What happens during the flocculation process in water treatment?

Gentle mixing promotes particle collisions and growth of larger settleable flocs

Which chemical is commonly used for fluoridation with 45% fluoride ion content?
A) Sodium fluorosilicate
B) Sodium fluoride
C) Hydrofluosilicic acid
D) Calcium fluoride

B) Sodium fluoride

Why does alum addition consume alkalinity in water treatment?

Alum reacts with natural alkalinity producing CO₂ and consuming bicarbonate ions

Typical filtration rates for conventional rapid sand filters range from _____ gpm/ft².

2 to 4

True or False: Powdered activated carbon is removed by regeneration with sodium hydroxide.

False. PAC is removed by clarification and filtration, not regeneration.

What indicates that a jar test coagulant dose is excessive?

Formation of pinfloc and increasing turbidity due to restabilization

A clarifier with 1000 m² surface area treating 2000 m³/day has an overflow rate of _____ m³/day/m².

2