Compost refining techniques include adaptations of the separation and size reduction techniques already described in the Critical Review Sections: Pre-Processing Methods - Separation Technologies and Pre-Processing Methods - Size Reduction. In addition, operations may include the production of fine pellets (around 5 mm diameter) from composts, and/or bagging of the compost (Newport 1990). A number of developmental techniques have also been evaluated, for example the use of electric fields or chelating agents for the removal of trace elements from composts.
For the most part the “product” is the organic rich fraction. However, dense fractions with low organic content (for example rich in glass and ceramics) may be of use in landfill as daily cover or in drainage layers.
This chapter considers:
· separation processes applied in refining
· fine milling and pelleting
· mixing and bagging
· other techniques (largely experimental).