CHARACTERIZATION OF URBAN WASTES ACCORDING TO FERTILITY AND PHYTOTOXICITY PARAMETERS

Several urban wastes of different nature and level of organic matter s tability (municipal solid wastes, sewage sludges and composts) have be en characterized analysing fertility and phytotoxicity parameters. Sew age sludges showed the highest N and P values of all the wastes. The t otal K content of the wastes was low but almost all was available to p lants. Mature composts had the lowest organic carbon and humic substan ces values as a consequence of organic matter mineralization during th e composting process. The soluble C at pH 2/precipitated C ratio decre ased as the stability of the organic matter increased. In spite of the heterogeneity of the wastes analysed, the organic matter/total organi c C ratio was largely constant with a mean value of 2.05. In no case d id the heavy metal levels exceed the maximum allowed by the EU disposi tion for sewage sludges use in agriculture. The highest levels of phyt otoxic substances occurred in the fresh wastes. The germination rates and root length were highest with mature composts. Germination index a nd root length were negatively correlated with water soluble carbon (W SC) and WSC/N ratio. The principal component analysis showed that extr actable C, soluble C at pH 2 and water soluble C were the C fractions which most contributed to the total variability. (C) 1997 ISWA.