REMOVAL OF DISSOLVED ORGANIC CARBON AND BROMIDE BY A HYBRID ANION EXCHANGE-ULTRAFILTRATION SYSTEM

摘要

Dissolved organic carbon (DOC) and bromide (Br) are principal precursors in the formation of halogenated disinfection by-products resulting from chlorination of drinking water. Their effective removal from water represents, thus, one of the main challenges faced by drinking water treatment plants worldwide. The objective of this study was to evaluate the performance of a hybrid system based on the patented magnetic ion-exchange resin (MIEX~R combined with ultrafiltration (UF) in the removal of DOC and Br from water. The DOC removal was further investigated according to the molecular size distribution by high-performance size-exclusion chromatography (HPSEC) to identify which organic fractions were preferentially removed by the MIEX/UF process.The pilot-scale hybrid MIEX/UF system was composed of a stirred tank where feed water was contacted in a fluidized bed mode with the MIEX resin followed by a UF module operating in an inside-out cross-flow filtration mode. Both concentrate and permeate streams from the UF unit were recirculated into the feed tank. Two different doses of MIEX (1 mL/L and 3 mL/L) were applied and compared. Samples of feed water, UF permeate and tank solution were regularly collected to assess the system performance in terms of removal of DOC and Br-.Results demonstrated that the hybrid MIEX/UF system was able to remove TOC from water. The removal depended upon the MIEX dose applied. At a MIEX dose of 3 mL/L, the TOC removal was persistent over the 18-hr experiment at 48%. However, at a MIEX dose of 1 mL/L the removal ceased after 14 hr indicating likely saturation of MIEX towards TOC. With regard to Br-, the observed initial removals were lower (25% and 40% at MIEX dose of 1 mL/L and 3 mL/L, respectively), and they decreased to zero over the experiment indicating saturation of MIEX toward Br- at both doses. Fractionation of DOC by HPSEC indicated that the highest molecular weight fraction was mainly removed by size-exclusion by the UF membrane, while lower molecular weight fractions seemed to be better removed by ion-exchange on the MIEX resin.