Chemical and biological properties of composts produced from organic waste

The aim of the investigations was to determine the effect of composting municipal waste with various added substances (starch, edible oil or urea) on the content of selected forms of zinc, cadmium, copper and lead, the quality of organic matter and counts of some groups of physiological microorganisms. The above properties of compost may provide the basis for assessment of the composting process efficiency. The research object was biomass prepared from plant and other biodegradable waste generated in the area of Krakow. The biomass for composting was prepared from the following organic waste: deciduous tree chips, chicory coffee production waste, grass and tobacco waste. There were two stages of the composting process: I – lasting for 14 days, to obtain “heated” compost, and II – lasting for 210 days, when starch, edible oil or urea was added to the composted biomass. The total content of Zn, Cd, Cu and Pb determined in the analyzed composts does not pose a threat to the purity of the soil environment. The content of water-soluble forms of trace elements and forms bound to organic matter was affected by the loss of organic matter, chemical properties of a given element and the addition of supplement, mainly urea, to the composted biomass. Analysis of the fractional composition of humic compounds revealed higher values of the Cha:Cfa ratio in the composts with added edible oil or urea than in the other composts, which may indicate a much more advanced decomposition process of the material subjected to composting. Among the analyzed microorganisms, bacteria were most numerous in the composts. The introduction of urea to the composted biomass reduced microbial activity. Adding starch or oil stimulated microbial development and may have stimulated the composting process.