Determination of maturity indices for city refuse composts

A composting experiment was carried out to study which are the best parameters to use as indicators of the degree of compost maturity, and to determine ‘humification’ indices for practical use. The following parameters were selected: cation exchange capacity (CEC), carbon/organic nitrogen ratio in water extract ( C N w ), C N ratio in solid phase ( C N s ), total organic carbon ( C t ), oxidizable carbon ( C o ), alkaline-extractable carbon ( C ex ), humic and fulvic-like carbon ( C ha , C fa ) humification ratio ( HR = C ex C o ×100 ), humification index ( H 1= C ha C o ×100 ), percent humic acid ( P ha = C ha C ex ×100 ) and C ha C fa ratio. The regression analysis shows that the carbon (total and oxidizable), C N s , C N w , CEC , Hl, P ha and C ha C fa ratio are correlated with a level of significance higher than 99.5%. From the integration of the deduced values, applying the obtained equations sequentially, the optimal values of these parameters to assure an acceptable degree of maturity of the compost are: C N s < 12, C N w < 6, CEC > 67 mEq per 100 g (on an ash-free basis), C ha C fa > 1.6, Hl > 13% and P ha > 62%.