A bench-scale study evaluated the impact of introducing desalinated seawater into the San Diego County Water Authority’s system so it would not adversely impact water quality.

By Ufuk G. Erdal, Ph.D., P.E., CH2M HILL Global Technology Leader; Jim Lozier, P.E., CH2M HILL Technology Fellow; and Tim Suydam, San Diego County Water Authority

Ufuk Erdal and Jim Lozier, along with co-author Tim Suydam of the San Diego County Water Authority will present their paper “Chloramine Stability And DBP Formation In Distribution System Carrying Blended Stream Of Desalinated And Treated Surface Waters” on Tuesday, June 11 at 2:30 p.m., during the American Water Works Association’s Annual Conference and Exposition (ACE 13), in Denver, Colorado.  Learn more about CH2M HILL’s ACE 13 2013 participation and technical sessions.

The San Diego County Water Authority (Water Authority) is planning to accept desalinated seawater (DSW) from a proposed 50 mgd seawater desalination plant in Carlsbad, California, at some point in the future. Water Authority intends to blend disinfected DSW with Twin Oaks Valley Water Treatment Plant (TOVWTP) treated surface water (TSW) in the TOVWTP’s Clearwells. In the short term, DSW may also be blended with treated water from the Metropolitan Water District (MWD) in one of the Water Authority’s distribution pipelines. While DSW will provide an important new source of drinking water for San Diego County residents, several factors must be considered to ensure that the introduction of DSW into the Water Authority’s system will not adversely impact water quality.

Our presentation provides an overview of a comprehensive bench-scale study that CH2M HILL conducted to evaluate the impact of DSW bromide level on chloramines decay and disinfection stability, quantify the amount of chlorine boosting necessary to maintain a target chloramine level after blending, determine boosting location(s) to minimize operating cost and evaluate disinfection byproduct formation potential for blended streams of DSW and TSWs. We will describe the testing methodology and outcomes of the study.

As stated above, a key consideration for the blending of DSW and TSW is the potential for the higher bromide levels in DSW to cause a loss in chloramine residual.  Interactions between bromide and chloramines are complex, and dependent on numerous case-specific factors including: initial bromide concentration, pH, alkalinity, and TOC levels, primary disinfection conditions for DSW, DSW conveyance time and relative contribution of DSW to blended water, disinfection protocol and methods for chemical addition (i.e., pre-formed versus sequential or conventional chloramination). Although considerable research has been performed to determine the impacts of several of these factors on disinfectant residual stability, the degree of differences in the published (and unpublished) literature did not provide a clear path for adoption of a reliable full-scale blending strategy without the need for empirical information. Therefore, we conducted a comprehensive bench-scale study in order to:

  • Evaluate the impact of DSW quality, and in particular bromide level, on chloramine decay
  • Quantify an acceptable level of bromide in DSW (from the Carlsbad desalination facility) to minimize chloramine decay when DSW and TSW are blended
  • Where chloramine decay occurs, quantify the amount of chlorine boosting necessary to maintain a target chloramine level
  • Determine optimum chloramine boosting location(s) to minimize operating cost

In addition, the Water Authority was also interested determining in the impact of blending on disinfection byproduct formation and nitrification during distribution. Therefore, the study also evaluated:

  • Disinfection byproduct formation potential for blended streams of DSW and TSWs
  • Nitrification potential during distribution

The information covered in our presentation is particularly valuable for agencies and consultants who are considering use of seawater desalination as a means to supplement current water supplies, and plan to introduce desalinated seawater into their existing distribution system.

Dr. Erdal is a Global Technology Leader for CH2M HILL, specializing in evaluating and assessing performance of treatment unit processes for wastewater and reuse, process optimization, design and costing of wastewater, water reuse, biosolids and residual disposal, advanced water treatment facilities, desalination, water stabilization and chemical feed and storage systems. He is also a leading expert for evaluating fate and transformation of compounds of emerging concerns thru conventional and advanced treatment processes.

Mr. Lozier is one of only five Technology Fellows within the CH2M HILL Water Business Group’s global technology organization and works on a worldwide basis on the application of desalination technologies for the production of drinking and high quality industrial water from seawater, brackish water and wastewater sources, including concentrate. Mr. Lozier specializes in the study, design, and operation of desalination systems utilizing reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and electrodialysis as well as mechanically driven distillation processes.