AWWA ACE58294

Carbon literature is rich in methods on carbon synthesis and surface modification to preparematerials with desired physicochemical properties for a particular type of application. Ourunderstanding about dissolved organic matter (DOM) and its adsorption by granular activated carbon (GAC) have greatly improved within the pasttwo decades. Therefore, the main objective of this research was to develop tailored activatedcarbons for enhanced and selective removal of DOM from natural waters. Based on the largesize of the DOM, it is hypothesized that the proper type of adsorbents for this applicationshould have a sufficient amount of mesoporosity (i.e., a larger fraction of pore volume andsurface area should be in the pores >2nm). At the same time, DOM is a heterogenous mixtureof polar molecules with negatively charged and acidic functionalities in natural waters. Due totheir hydrophilic nature, solvent-motivated adsorption (i.e., hydrophobicity effect) is notexpected to play a major role in the removal of DOM molecules by GAC from water.Therefore, it is further hypothesized that for enhanced and effective DOM removal, the carbonsurface should have basic properties, carry an overall positive charge, carry specificfunctionalities, or an optimum combination of all these characteristics.It is possible to control carbon porosity by either selecting starting materials with differentporosities or enlarging micropores of a sorbent using different treatment schemes. Bothapproaches were used in this study. Three GACs (microporous F400, mesoporous WVBMESOand WVB-MACRO) were selected as sorbents. Obtained results of virgin andmodified F400 carbons are presented and discussed in this paper. A similar study ofmesoporous carbons is in progress.Each carbon surface was modified using three main approaches: heat treatment under He orH2 atmosphere; NH3 treatment at low and high temperatures with or without pre-oxidationwith HNO3; and, iron impregnation. Heat and ammonia treatments enhance the basicity ofcarbon surface. In addition, ammonia treatment at different temperatures introduces variousnitrogen-containing functionalities to the carbon surface, which may interact with DOMcomponents. Oxidation followed by ammonia treatment enlarges carbon pores whileincreasing the value of surface basicity and the number of nitrogen-containing functionalities.Iron cations, or even zero-valent iron, dispersed on the carbon surface can significantlyenhance affinity of DOM components toward the carbon surface. Recent results obtainedduring the development of enhanced coagulation guidelines indicated that it is possible toremove more DOC using iron coagulants, compared with aluminum coagulants (Randtke, etal., 1999; Edwards, 1997). Data indicated also that some fractions of non-removable DOM byalum could be removed by iron chloride. Therefore, it is expected that DOM uptake by GACsbe increased by promoting: electrostatic attractions between cationic iron species andanionic DOM molecules; and/or favorable complex formation between the iron and DOMspecies.Since various treatment routes have been used to prepare different sorbents, the modifiedcarbons were named with abbreviation codes describing the treatment procedures employed: He: heat treatment at 900C for 2hr under helium flow; H: heat treatment at 900C for 2hrunder hydrogen flow; 16NO: oxidation by using boiling concentrated nitric acid for 1hr;8N2H: treatment with ammonia at 800C for 2hr; 4N1H: treatment with ammonia at400C for 1hr; and, Fe3E and FeS: iron impregnation by ion exchange and incipientwetness methods, respectively. For example F400-He-16NO is the F400 carbon that was heattreated under helium and then oxidized with concentrated nitric acid. Virgin and modifiedcarbons were characterized by surface area and pore size distribution analysis, pHPZC,elemental analysis, water vapor adsoption, acid/base uptake, and iron analysis of digestedsamples.DOM samples we

Product Details

Edition:

Vol. - No.

Published:

06/15/2003

Number of Pages:

8

File Size:

1 file , 300 KB