SEPARATELY COLLECTED ORGANIC HOUSEHOLD WASTES - CHEMICAL-COMPOSITION AND COMPOSTING CHARACTERISTICS

The purpose of this investigation was to characterize composts derived from sorted and separately collected organic household wastes, and to investigate the chemical changes taking place during their composting. In two compost piles, one consisting of pure organic household wastes and the other of a mixture of organic household and park wastes (50/50 vol.%), pH values increased from ca. 5 to 8.3 and ash contents from around 30% to 61% after 6 months of composting. Fatty acids were detected in both compost piles up to 5 months, highest concentrations were measured after one month, 8.9 and 2.95% in dry matter. Sodium contents in organic household composts were relatively high, amounting to 0.4-0.6% in dry matter. The highest mean temperatures in the composts were 68 and 74 degrees C. Temperature declined after 3 months to reach the same level as the ambient air after 6 months. Heavy metal contents in the composts investigated were much lower than in composts made from unsorted household wastes. Apart from lead, which exceeded 100 mg kg(-1), concentrations were lower than the recommended maximum values as outlined by the Swedish Environmental Protection Agency (SNV, 1990). Composts produced in home gardens partially consisting of organic household wastes, which were used as a standard of reference, had still lower heavy metal contents. This may be explained by the 3% foreign components and unwanted impurities, which were still found in the separately collected organic household wastes. Total gaseous N losses during composting amounted to 51.6% for the organic household wastes and 26.2% for the mixture of organic household and park wastes, which was of the same magnitude as in animal manures.