Removal of dissolved natural organic matter and control of disinfection by-products by modified activated carbons.

摘要

The main objective of this study was to conduct a systematic investigation for developing a fundamental understanding of how activated carbons should be tailored for enhanced removal of dissolved natural organic matter (DOM) from natural waters and the impact on disinfection by-product (DBP) control at typical drinking water treatment conditions.; Various combinations of liquid and gas phase treatment pathways were employed to modify the commercial granular activated carbons and to examine the adsorption of DOM from natural waters. Iron-impregnated and ammonia-treated pre-oxidized activated carbons showed significantly higher DOM uptakes than the virgin GAC. The enhanced DOM uptake by iron-impregnated carbon was attributed to the presence of iron species on the carbon surface. The higher uptake of ammonia treated carbon was due to the enlarged carbon pores and basic surface created during the treatment. No specific selectivity in the removal of different DOM components was observed as a result of carbon modification. The isotherm results of two activated carbon fibers and size exclusion chromatography results showed that only carbon pores larger than 1nm were accessible to DOM molecules.; Enlargement of carbon pores by steam treatment and its impact on DOM removal and DBP control were further investigated. Rapid small scale column tests showed that steam-treated carbons had significantly longer filter bed operation time for DBP control than the precursor. However, the extent of DOM removal and DBP control was water specific and increased with decreasing pH. UV254 absorbing DOM molecules mainly contributed to the DBP formation in water treatment. The results showed that activated carbons with large surface areas and pore volume in pores > 1nm and basic pHPZC values are expected to exhibit high degree of DOM removal and to be more effective for DBP control. It also appears that such GACs will provide better DBP control in high than low SUVA254 waters.; Various iron impregnation methods were investigated to study the iron effect on the DOM removal. The results indicated that various factors including iron dispersion and the form of iron species affect the DOM removal by iron-impregnated carbons. GACs prepared by ion-exchange methods exhibited higher DOM removal than their precursor in isotherm experiments. However, no clear effects of iron impregnation were observed in RSSCT experiments as compared to the precursor GAC. This was attributed to different adsorption pattern between isotherm and column experiments.; This study also demonstrated that it is essential to conduct a RSSCT combined with DBP measurements, despite its longer and more costly experimental nature compared to batch isotherm, in order to evaluate the effectiveness and feasibility of a GAC for DBP control in drinking water treatment.