Evaluation of a Magnetic Ion Exchange Resin for the Removal of Disinfeection By-Product Precursors: A Pilot Plant Study

The objective of this investigation was to evaluate the effectiveness of a magnetic ion exchange process (MIEX) for the removal of disinfection by-product (DBP) precursors (dissolved organic carbon (DOC) and bromide) from drinking water based on a continuous-flow pilot plant study. A 10-gpm MIEX pilot plant was designed and operated by Black and Veatch Consulting Engineers. The pilot plant was operated continuously for 4-5 weeks at four different sites across the United States. The sites were chosen to provide a range of different raw water qualities. Variables examined in the pilot plant study were resin dose, contact time, and regeneration frequency. Influent and effluent samples were taken from the pilot plant on a regular basis and analyzed for ultraviolet (UV) absorbance at 254 nm (UV254), DOC, bromide, and several other selected contaminants specific to the water being evaluated. Jar tests were also performed on several of the waters to determine the impact of MIEX pretreatment on subsequent coagulation. Samples of the raw water, MIEX-treated water, and coagulated water with and without MIEX pretreatment were also subjected to hydrophobic/hydrophilic fractionation, molecular size characterization, and chlorination under uniform formation conditions to determine the concentration and speciation of DBP, trihalomethane (THM) and haloacetic acid (HAA) precursors. The results indicated that MIEX removed a substantial amount of DOC and UV-absorbing materials, except in one of the waters that had a high total dissolved solids concentration. MIEX decreased overall THM and HAA formation upon subsequent chlorination. The MIEX-treated water had lower THM and HAA formation potentials than the raw water or the coagulated water that was not subjected to MIEX pretreatment. However, DBP speciation after MIEX treatment shifted from the fully chlorinated THM and HAA components to the more highly brominated compounds as a result of the limited removal of bromide relative to DOC. MIEX removed a higher fraction of the large molecular weight organic compounds than the smaller ones, but removed more of the smaller molecules than coagulation. MIEX also removed some of the hydrophobic, transphilic, and hydrophilic fractions of the DOC, but removed the hydrophobic material to a greater extent. It removed more of the transphilic and hydrophilic fractions of the DOC than coagulation. MIEX also removed bromide to some degree. Bromide removal was dependent on the presence of other anions in the raw water, e.g. bicarbonate, sulfate, and on the type of salt used in the regenerant brine.Master of Science in Environmental Engineerin