Compost quality: Physical characteristics, nutrient content, heavy metals and organic chemicals

Abstract

Bio‐ and yard waste composts show a high standard of quality. Due to their valuable characteristics it is possible to utilize them in plant production. Average heavy metal contents of bio‐ and yard waste composts is low. Nevertheless, the results presented reveal that nine biocomposts do not comply with the requirements necessary to obtain the “seal of approval for quality compost”;. A first check of the data suggests that soil contamination of geological, respectively pedological origin, is responsible for limit violation. Other limit violations are due to increased soil contaminant levels, caused by anthropogenic activities. Increased heavy metal contents in two more composts is likely due for above average degree of undesirable materials in the separately collected organic refuse. Dioxins can be found ubiquitously in the environment, consequently therefore in composting raw material and in the end product. According to current knowledge, levels of PCDD/F found in bio‐ and greencompost can be classified as low. It is recommended to urgently standard use the separate collection and processing methods of bio‐ and yard waste compost to minimize the introduction of organic trace contaminants. This is the most efficient way to reduce the introduction of contaminants. Furthermore, it is urgently demanded to eliminate all sources of dioxins and PCB, such as specific thermal processes (e.g. cable pyrolysis) and chlorinated chemicals (e.g. PCP), to prevent the further addition of these substances. Irrespective of the current contents of organic trace contaminants in compost, there is generally a considerable need for research in the field of contaminant transfer (soil‐plant; plant‐animal; animal‐human being) and in the field of contaminant metabolism, both in the soil and during the composting process. Further knowledge is also needed with regard to their formation and origin.