Composts derived from mechanically segregated MSW have several properties which may be of potential benefit for soil improvement and restoration or in growing media, as well as a pre-treatment prior to landfill. These are:
· a limited (and slowly available) content of plant nutrients, such as nitrogen, phosphorous, potassium, calcium, magnesium and trace elements
· stabilised organic matter
· a liming effect
· biological activity.
Not all of these benefits are suitable for all applications, see the Critical Review Section, End-uses.
However, composts derived from mechanically segregated MSW also may have several properties which might be deleterious for these applications, and which may cause wider environmental impacts from the compost application. These might include:
· excessive trace element contents
· excessive content of toxic organic compounds
· lack of stability or maturity
· impacts from migration of nitrogen and enrichment of phosphorous or nitrogen immobilisation
· deleterious organisms
· excessive content of “inerts”
This chapter reviews the following compost properties and the significance to compost applications and the wider environment:
· physical properties
· major chemical properties
· trace elements
· organic pollutants
· microbial and pathogen issues
· maturity and stability.
Note moisture contents of finished, matured refined MSW-derived composts tends to be 40 to 60% on a fresh weight basis, bulk density 500 kg.m-3.