Field Testing and Cost-benefit Analysis of Anoxic/Anaerobic Selectors

Anoxic and anaerobic selector zones used at the front end of wastewater treatment plants have been shown to improve the settleability of the activated sludge. These zones encourage the growth of bacteria that form denser and heavier flocs. The Broward County North Regional Wastewater Treatment Plant in Southeast Florida implemented anoxic zones at the front end of a 20-mgd module provided with fine bubble diffusers to demonstrate enhanced total nitrogen removal and sludge settleability improvements. The SVI values over the course of the study were consistently less than 100 mL/g; the average value was 75 mL/g, down from an average of 141 mL/g prior to the implementation of the selector zone. A State Point Analysis determined that this improvement in SVI would allow the plant to use the existing four clarifiers for future conditions rather than adding a fifth one, saving over 4,000,000 in new construction plus allowing O&M cost savings.