Humification index (HI) as evaluation of the stabilization degree during composting

Abstract

The stabilization of a pile of ground urban refuse was monitored during five months. Carbon dioxide evolution, temperature, moisture level, organic matter, and pH were measured regularly. The humification index (HI) of organic matter extracted by 0.1 M Na₄P₂O₇ plus 0.1 M NaOH was found to decrease linearly with time during the thermophilic phase from about 1.4 to 0.4. Turning of the pile caused a drop in the HI values, but the index increased again every time the temperature of the static pile reached 65°C. The value of the humification index in water extracts (HIw) reached a maximum after 4 d in the superficial layers and after 11 d at a depth of 30 cm. HIw values were found to decrease hyperbolically with time during the thermophilic phase.