MATURITY AND STABILITY PARAMETERS OF COMPOSTS PREPARED WITH A WIDE-RANGE OF ORGANIC WASTES

Seven different composts were prepared in a pilot plant by the Rutgers static-pile system using a wide range of wastes: sewage sludge, poult ry manure, pig slurry, olive-mill wastewater city refuse and the ligno cellulosic wastes cotton waste, maize straw and sweet sorghum bagasse. Their chemical and biological properties were studied at four stages of the composting process: in the initial mixture, at the thermophilic phase, at the end of the active phase and after two months of maturat ion. The following maturity indices were established: C/N < 12, C-W < 1.7%, C-W/N-org < 0.55, NH4/NO3 < 0.16, and NH4-N < 0.04%, with a germ ination index greater than 50%. In addition, some carbon mineralizatio n parameters could also be used as maturity indices: mineralized-C in 70 days (C-m) < 30%, rapidly mineralizable-C (C-R) < 7.2% and a slow m ineralization rate (C-s x K-s) < 0.35% day(-1). Maturation indices bas ed on humification of the organic matter and the cation exchange capac ity of different composts could not be found, since the values for mat ure compost depended on the wastes from which the composts were made. (C) 1998 Elsevier Science Ltd.