[Show abstract][Hide abstract]ABSTRACT: Humic acids (HAs) that extracted from leachates from semi-aerobic and anaerobic landfills test field at different stabilization times were characterized by elemental composition, Fourier transform infrared spectroscopy (FTIR), and Carbon-13 Cross-Polarization Magic-Angle-Spinning Nuclear Magnetic Resonance (13C CP/MAS NMR). The higher sulfur (S) content of HA in the anaerobic landfill leachate after a short stabilization time showed that the S released from the organic matter degradation was more easily stabilized under anaerobic conditions, which indicate that HA from anaerobic landfill leachate was more chemically reactive and played a more important role in mobilizing heavy metal, especially mercury, at early landfill stabilization times. However, the S content of HA from the semi-aerobic landfill increased over time, suggesting that more S was stabilized in HA as the landfill stabilization time was extended. The analytical results for the FTIR and NMR showed that the HA from the anaerobic landfill contained more aromatic groups, while HA from the semi-aerobic landfill had more oxygen-containing groups. The aromatic components of the HA from both the anaerobic and semi-aerobic landfills increased over time, suggesting that the maturity and humification degree of HA increased during the stabilization process.
[Show abstract][Hide abstract]ABSTRACT: Fluorescence excitation-emission matrix spectroscopy (EEMs) combined with fluorescence regional integration (FRI) analysis was used to investigate the composition and transformation of humic acid (HA) and fulvic acid (FA) from landfill. The EEMs of HAs at different landfill ages were characterized by two typical fluorescence chromophores with Ex/Em pairs at Ex=420-470 nm/Em=490-530 nm and Ex=345-375 nm/Em=450-465 nm. EEMs of FA were featured by other two distinctly different fluorophores with Ex/Em pairs at Ex=315-335 nm/Em=420-440 nm and Ex=255-275 nm/Em=425-455 nm. The results show that HA extracted from the refuse disposed in the year of 1989 was formed by connecting small-condensed aromatic structures with protein-like chains. Compared with HA extracted from the refuse disposed in the year of 1992, HA extracted from the refuse of 1996 had a higher fluorescence intensity and lower r(()(B)(,)(A)()) (the ratio of the fluorescence intensities of peak B and peak A) value. It contained low molar mass components, low aromatic condensation degree, and more easily oxidized substituents. This indicates that the landfill time strongly affects the EEMs characteristics of HA, and that the humification degree of HA increases with the landfill time. A red shift to a longer wavelength region and an increase of fluorescence intensity were observed when the concentration of HA was increased, suggesting that concentration had a great influence on the fluorescence characteristics of HAs. pH (2-12) also had significant effects on the fluorescence intensity, although it exerted no effect on the peak position of fluorescence of HA and FA. The results of FRI show that increasing concentration lead to more interactions among various structure components and that small molecular weight units tend to aggregate or be masked into more complicated and larger structures. The pH influence on the fluorescence intensity of HA seems mainly through molecular configuration, while the fluorescence intensity change with pH may be due to various substituents of FA.
No preview · Article · Nov 2011 · Waste Management
[Show abstract][Hide abstract]ABSTRACT: Mercury (Hg) distribution and migration in different landfill stabilization processes were evaluated in this study. Wide ranges of Hg concentrations were observed because of the heterogeneity and variability of landfill refuse. In addition, temporally variable conditions, including pH, organic matter, and vegetation cover, which influence Hg migration in landfills, may also affect the temporal distribution of Hg in landfill refuse. The main fraction of Hg, elemental Hg, decreased with time, while the stable fractions of Hg increased. The fulvic acid (FA) extracted from the landfill leachate had much lower overall Hg-complexation stability constants, which suggests that organic S groups might have been rapidly saturated by small amounts of Hg while leaving oxygen functional groups, such as carboxylic functional or phenolic groups, acting as the primary binding sites for Hg.
No preview · Article · Apr 2011 · Journal of Environmental Monitoring