Which combination describes a low-cost PAC feed method suitable for secondary treatment?

Which combination describes a low-cost PAC feed method suitable for secondary treatment?

• A. Helix-type feeder, primary
• B. Helix-type feeder, secondary
• C. Slurry feed system, primary
• D. Slurry feed system, secondary

Answer: (B)

Dosing PAC at the secondary treatment stage with a dry PAC feed using a helix-type feeder provides a simple, cost-effective approach. The helix-type feeder is a screw-type device that delivers a precise, continuous amount of dry PAC into the mixing or rapid-mix area of secondary treatment, giving consistent distribution and adsorption without the need to dilute PAC into a slurry. Using dry PAC avoids the extra steps and equipment required to prepare and pump a PAC slurry, such as slurry tanks, mixers, and additional pumping energy, which lowers both capital and operating costs. This method integrates well with the secondary treatment process, where adsorption of dissolved organics occurs in the early mixing stage, improving overall effluent quality. In contrast, slurry feed systems require preparing and handling a PAC slurry, adding complexity, equipment, and cost, and concentrating PAC dosing at the primary stage is less effective for targeted removal during secondary treatment.

Dosing PAC at the secondary treatment stage with a dry PAC feed using a helix-type feeder provides a simple, cost-effective approach. The helix-type feeder is a screw-type device that delivers a precise, continuous amount of dry PAC into the mixing or rapid-mix area of secondary treatment, giving consistent distribution and adsorption without the need to dilute PAC into a slurry. Using dry PAC avoids the extra steps and equipment required to prepare and pump a PAC slurry, such as slurry tanks, mixers, and additional pumping energy, which lowers both capital and operating costs. This method integrates well with the secondary treatment process, where adsorption of dissolved organics occurs in the early mixing stage, improving overall effluent quality. In contrast, slurry feed systems require preparing and handling a PAC slurry, adding complexity, equipment, and cost, and concentrating PAC dosing at the primary stage is less effective for targeted removal during secondary treatment.