Advanced Technologies for Attaining and Maintaining DBP Compliance
- Allison Reinert, EIT, Scott Alpert, PE PhD, Mark Bishop, PE, Ben Stanford, PhD - Hazen and Sawyer
With more stringent disinfectant/disinfection byproduct (D/DBP) rules, and a potential Stage 3 DBP Rule on the horizon with the 6-year review of the D/DBP rules in 2016, utilities are evaluating advanced techniques to optimize their current treatment processes as well as look towards future treatment improvements. Granular activated carbon (GAC) adsorption is an advanced treatment option that has been proven effective for removal of DBP precursor organic matter, though proper monitoring and change out triggers are required to operate the system cost-effectively while attaining water quality goals. Additionally more emphasis has recently been placed on water quality monitoring to assess the DBP formation potential, allowing utilities to focus on the treatment strategies most effective at reducing DBP formation. As such, the principal objective of this presentation is to discuss several different pilots using GAC adsorption, fluorescence water quality monitoring, and online speciated THM analysis as options to optimize treatment to attain and maintain DBP compliance. The water treatment plants (WTPs) involved in these pilots span the state of North Carolina and provide insight into various water quality challenges for compliance.
In the first study, online THM monitoring (hourly sampling) at the point of entry was conducted for four months with concurrent water quality sampling, which captured a wide range of source water qualities. Three-dimensional excitation-emission fluorescence (EEM) sampling of the combined filter effluent was also conducted for one month. Coupling the online THM measurements with the EEM analysis, resulted in a predictive THM model with an R2 value of 0.96 for chloroform and 0.86 for bromoform prediction. Additional models were also created for each of the other speciated THMs and TTHM prediction which illustrated the influence of the bromide concentration in the source water.
Additionally, a second study was completed using GAC treatment was coupled with fluorescence analysis. This particular GAC pilot evaluated several different optimization strategies for DBP compliance, including preforming DBPs with raw water chlorination for subsequent adsorption removal, various empty bed contact times, and various source water conditions. Fluorescence measurements taken periodically throughout the study and coupled with DBP analysis were able to provide insight into how pre-chlorination changes the reactive organic matter through the columns as well as the DBPs that would reach the distribution system.
The discussion of these pilots provides utilities with insight into how best to pilot and potentially study their WTP to optimize treatment for DBP compliance in challenging source water conditions. Piloting of various treatments as well as analysis technologies has allowed the utilities involved in these studies to make informed decisions on how to better optimize treatment and on which instruments might be beneficial to include in regular analysis for better meeting and exceeding their water quality goals.
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