Structural investigation of isolated aquatic fulvic and humic acids in seepage water of waste deposits by pyrolysis-gas chromatography/mass spectrometry

Fulvic and humic acids isolated from seepage waters of four municipal waste landfills and one hazardous waste landfill were analysed by Curie point pyrolysis-gas chromatography/mass spectrometry (Py---GC/MS). Furthermore, fulvic and humic acids were subjected to acid hydrolysis followed by alkaline hydrolysis. The hydrolysis products were analysed by gas chromatography/mass spectrometry (GC/MS) and the residues by Py---GC/MS. Results show that the pyrolysis products of the fulvic and humic acids at a pyrolysis temperature of 770°C are similar before and after acid/alkaline hydrolysis. The pyrolysis products are composed mainly of aromatic compounds like alkylbenzenes, alkylnaphthalenes and higher condensed aromatic substances; aliphatic constituents are detectable only in trace amounts. At a pyrolysis temperature of 510°C the pyroloysis products of the isolated fulvic and humic acids are dominated by benzoic acids, phenols and straight chain acids. The compound composition is similar to the one obtained from GC/MS analysis of the soluble hydrolysis products. Results indicate that the fulvic and humic substances from leachate water of waste deposits are built up of an aromatic nucleus, which is not completely decomposed upon pyrolysis at 510°C. The nucleus seems to be surrounded by hydrolysable structural units composed of aromatic acids and phenols linked via ester and ether bonds to the fulvic respectively humic acid core. Comparison with pyrolysis products obtained from soil humic substnaces indicates a higher degree of aromaticity and thermal stability of part of the macromolecular network. In addition results indicate that the structural composition of the fulvic and humic acids in leachate waters from waste deposits is independent from leachate quality.