Towards Defining Maturity of Composed Municipal Solid Waste: Transformation of the Organic Matter to Humic Substances
(GIF)

The humification process of organic mater in compost was investigated by characterization of different aqueous extracts. The samples were analyzed by several chemical/physical, chromatographical, spectroscopical and biological tests. The amount of the DOC, extracted with water, is decreasing exponentially to around 400 mg/L DOC after 187 days of composting. This shows that after a short time the organic substances soluble in water are decreasing with composting time. The composition of the organic substances is changing during humification by producing organic substances showing higher spectral absorption activity. It is obvious that the Zn concentration is not changing during time of composting. However, Cu, Cr and Pb are increasing with time in the dissolved extracts. In general the gelchromatograms gained by DOC and UV-detection show the same shape. In case of the aqueous water extracts between 50 to 60 % of the DOC is attributed to a high molecular weight fraction. The nominal molecular weight, as gained after calibration by polysaccharides and polyethylens, is decreasing with time of composting. During composting the relative amount of the hydrophilic and hydrophobic fraction is not changing so much. The total amount of bounded amino acids is about 7 - 9 % of the DOC. The highest concentration of amino acids (carbon of the amino acids) is around 20 µg/mg DOC (aspartic acid, glutamic acid, cysteine and arginine). It is obvious that aspartic and glutamic acid are decreasing with composting time. The hydrolyzable polysaccharides are changing during time of composting.