Characterization of humic substances present in landfill leachates with different landfill ages and its implications

Abstract

Humic and fulvic acids extracted from landfill leachates were characterized using elemental analysis and various spectroscopic methods. Molecular size distribution of the humic substances (HS) was also determined using batch ultrafiltration technique and permeation coefficient model. The element analysis and spectral features obtained from UV/visible, IR, and 1H and 13C NMR showed that the aromatic character in the leachate HS was relatively lower than that of commercial humic acid (Aldrich Co.), and higher in the HS of older landfill leachate. Fluorescence spectra indicated that humic acids had a relatively higher content of condensed aromatic compounds than the fulvic acids obtained from the same sources, and the spectrum of commercial humic acid showed that aromatic compounds may be present in a much more condensed and complex form. Molecular size distribution data revealed that the leachate humic acids contained a higher percentage of smaller molecules of <10,000 D, compared with that of the commercial humic acid (45∼49% vs. 33%), and molecular size of the leachate HS had a tendency to increase as landfill age increased. These results indicate that the HS from landfill leachates were in an early stage of humification, and the degree of humification increased as the landfilling age increased, which implies important information on various related researches, such as interactions of HA with pollutants in terrestrial environments, and optimization of leachate treatment processes with respect to landfill age.