EVALUATION OF URBAN SOLID WASTE AND SEWAGE SLUDGE COMPOSTS AS COMPONENTS OF GROWING MEDIA

Some types of compost can be used as plant growing media to fully or partially replace traditional materials such as peat. Its use as a growing medium is probably the most demanding for compost because successful development of the crop relies heavily on some physical, chemical and biological properties of the substrate. Although only high-quality compost should therefore be used for this purpose, materials of a lower quality may also be useful if mixed in appropriate proportions with others. Thoroughly characterizing a material allows its potential as a substrate to be assessed and any constraints on its use identified. In this work, two different composts obtained from the organic fractions of urban solid waste and another two from sewage sludge were evaluated as peat substitutes. The four composts exhibited poor water retention, high electrical conductivity, and also high levels of soluble ammonium, sodium and potassium. In addition, they were inadequately stable or mature (particularly those from sewage sludge). Therefore, if any of these materials is to be used as a plant substrate component, its proportion in the growing medium should never exceed 25%.