System Sizing & Design Flashcards

A designer must size a carbon filter to achieve a chloramine reduction EBCT of 10 minutes at 6 gpm service flow. What minimum carbon bed volume (in gallons) is required?

Answer: 60 gallons

Bed volume (gallons) = flow rate (gpm) × EBCT (min) = 6 gpm × 10 min = 60 gallons of carbon media.

When a water analysis shows iron at 3 mg/L AND hydrogen sulfide at 0.5 mg/L, which single-pass system design is most appropriate?

Answer: Oxidizing filter with continuous chemical oxidant feed followed by backwashing media

Both ferrous iron and hydrogen sulfide require oxidation before filtration; a chemical oxidant (such as chlorine) followed by backwashing catalytic or greensand media addresses both contaminants.

A system designer notes that the source water LSI (Langelier Saturation Index) is −2.0. What treatment concern does this indicate for system components?

Answer: Aggressive, corrosive water that may leach metals from piping and damage equipment

A strongly negative LSI indicates highly corrosive, undersaturated water that will dissolve calcium carbonate and aggressively attack metal piping and equipment.

For a commercial building, the designer specifies a 'lead-lag' configuration for two identical water softeners. What does this mean operationally?

Answer: The two softeners alternate between service and standby on a volume-triggered basis

In a lead-lag (alternating) configuration, one unit leads in service until its capacity is exhausted, then switches to standby (lag) while the other takes over.

A designer is calculating the salt efficiency of a softener regeneration. Using 6 lbs of salt to regenerate 20,000 grains of capacity, what is the salt efficiency?

Answer: 3,333 grains per pound

Salt efficiency = grains capacity ÷ lbs of salt = 20,000 ÷ 6 = 3,333 grains per pound.

In point-of-use RO system design, why is a post-filter (polishing carbon block) included after the storage tank?

Answer: To improve taste and remove any odors or contaminants absorbed from the storage tank bladder

The post-filter removes any tastes or odors that may accumulate in the storage tank and polishes the final water before delivery at the faucet.

A water treatment professional is sizing a whole-house system for a home with 3.5 bathrooms. Using the general rule of 1 bathroom = approximately 1 gpm peak demand, plus 1.5 gpm for kitchen and laundry, what service flow rate should the system be designed for?

Answer: 5 gpm

3.5 bathrooms × 1 gpm + 1.5 gpm (kitchen/laundry) = 5 gpm minimum service flow rate.