Development of engineered natural organic sorbents for environmental applications. 2. Sorption characteristics and capacities with respect to phenanthrene.

The effects of superheated water processing on enhancement of phenanthrene sorption by various source materials of natural organic matter (NOM) were systematically examined. Sorption capacities and subsequent phenanthrene retention characteristics of all organic materials tested were markedly increased by superheated water processing. Temperature effects on enhancement of the sorption behaviors of the test materials were greater than those of processing time, moisture content, and the presence of mineral catalysts. Greatest enhancement was observed for processing at 250 degrees C for 5 h with a moisture content of 50%. Strong correlations of sorption capacities and isotherm nonlinearities with processing temperature, and with the atomic ratios of oxygen to carbon (O/C), aromaticity, and hydrophobicity of the processed materials were observed. The sorption/desorption hysteresis indices of the processed materials also increased linearly with processing temperatures and O/C ratios. This is consistent with our observations of increased condensation and aromatization of NOM during superheated water processing presented in the first paper of this series. The relationships described provide direct experimental evidence that the sorption-desorption properties of NOM geosorbents are closely related to their degree of aromatization and condensation, and the work suggests strong potential for production of efficient and cost-effective engineered natural organic sorbents for environmental applications.