Strategies for Using Tank Aeration for Stage 2 DBP Compliance

Authors:

  • David S. Briley PE, Allison Reinert, and Erik Rosenfeldt PhD, PE - Hazen and Sawyer
  • Tiffanie Hawley - Cape Fear Public Utility Authority

Tank Aeration is gaining interest as lower cost alternative for Stage 2 DBP Rule compliance as compared to other compliance strategies. This method utilizes gas transfer principals to physically strip volatile THMs from finished drinking water and achieve reductions of 25 – 45 percent. Research as well as practical applications have shown that aeration can be effective even for the brominated THM species. This is of critical importance for water systems facing shifts to brominated species, and a resulting increase in mass concentrations of TTHMs, due to the presence of bromide into the water supply.

But, tank aeration is certainly not a panacea. One critical consideration for implementation of aeration is where to locate aeration treatment; at the water treatment plant or in tanks in the distribution system. Aeration at the water treatment plant provides for TTHM reductions throughout the distribution system. However, the size of the aeration system is larger, which affects capital and operating costs. Tank aeration systems in the distribution system can be more cost-effective since the systems are treating a smaller flow. However, aeration in a distribution system tank does not necessarily correspond with significant THM reductions at all Stage 2 monitoring locations. By carefully considering system hydraulics aided by a calibrated distribution system model, along with firm understanding of THM formation kinetics and the benefits and limitations of in-tank aeration for THM stripping, a methodology for evaluating the true impact of these technologies as Stage 2 DBP Rule compliance strategies has been developed.

This paper will present case studies evaluating THM removal for systems experiencing high levels of predominantly brominated THMs. The approach included:

1. Development of an in-tank aeration performance model to assess design variables such as THM speciation, formation kinetics, inlet THM levels, nozzle size, pumping rates, and water flow

2. Review of historical THM data to establish reduction goals.

3. Assessment of THM formation kinetics in the distribution system.

4. Evaluation of tank influence areas using a calibrated distribution system hydraulic model.

Ultimately, the work has resulted in development of effective strategies for Stage 2 DBPR compliance, inclusive of and reliant upon the inclusion of in-tank aeration processes.

For more information, please contact the author at dbriley@hazenandsawyer.com.

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