The role of surface acidity and pore size distribution in the adsorption of 2-methylisoborneol via powdered activated carbon

Abstract

Powdered activated carbon (PAC) is a common answer to water utilities’ taste and odor problems. However, these utilities are often uncertain as the characteristics of PAC are critical for optimum taste and odor abatement. In order to separate the effects, if any, that pore structure and surface chemistry have on the adsorption of the odorant 2-methylisoborneol (MIB), two sets of carbons were created: five physically activated (PA)-PACs, with different pore size distributions and similar surface chemistries, and four chemically treated (CT)-PACs with similar pore structures and different surface chemistries. Nitrogen adsorption, reverse mass titrations, and Boehm titrations were used to characterize the physical and chemical attributes of the carbons. Batch tests utilized 14C-MIB and contact times resembling those found at water utilities. The pore size distributions and the percent removal of MIB for the PA-PACs indicated that a range of micro- and meso-pores (12–100 Å) were necessary regardless of natural organic matter (NOM) concentration. The performance of the CT-PACs indicated that surface chemistry did affect MIB removal, but differently depending on the concentration of NOM. In DI water, surface acidity had a strong inverse relationship with MIB removal, but increasing NOM levels lowered the impact of the acidic functional groups. In fact, in a Florida raw water, surface chemistry demonstrated no effects on adsorption as all CT-PACs performed equally.