CHANGES IN HEAVY-METAL EXTRACTABILITY AND ORGANIC-MATTER FRACTIONS AFTER VERMICOMPOSTING OF SLUDGES FROM A PAPER-MILL INDUSTRY AND WASTE-WATER TREATMENT-PLANT

The aim of this study was to compare the quality of organic matter and the heavy metal composition in different mixtures of paper-mill sludg e and sewage sludge before and after a vermicomposting (Eisenia andrei ) process. A paper mill-sewage sludge mixture at a ratio of 1:6 (Wt/vo l) was the most effective in increasing the growth of earthworms. Para meters of humification showed that the organic matter in vermicomposti ng mixtures was not completely stabilized. Although total and DTPA-ext ractable metals increased after vermicomposting, the concentrations of these elements did not exceed the maximum limits permited in sludges for agricultural use.