A COMPREHENSIVE BENCH SCALE STUDY TO EVALUATE CHLORAMINE STABILITY AND DBP FORMATION IN DISTRIBUTION SYSTEM CARRYING BLENDED STREAM OF DESALINATED AND TREATED SURFACE WATERS

摘要

The San Diego County Water Authority (Water Authority) is planning to accept desalinated seawater (DSW) from Poseidon's 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. A comprehensive bench-scale study was 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. This paper presents testing methodology and outcomes of the study. The information presented in this paper will provide a great value 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.