Effect of barley straw and coniferous bark on humification process during sewage sludge composting.

This study investigated how different amendments (barley straw, coniferous bark) influence organic matter (OM) removal kinetics and humification during sewage sludge composting. With bark, high temperatures, intensive OM degradation and humification were achieved later than with straw. The rate of OM degradation was lower with bark than with straw (15.18 g/kg OM·d vs 24.07 g/kg OM·d) and the time needed for intensive HS formation was longer with bark (140 days vs 60 days). The kinetic constants for humic substances (HS) and humic acids (HA) formation were lower with bark than with straw (kHS 0.025 d-1 vs 0.047 d-1, kHA 0.022 d-1 vs 0.044 d-1). With bark, however, the increase in HS concentration during composting (Cmax,HS) was higher (178 mg C/g OM vs 84 mg C/g OM), and the fulvic fraction predominated in HS (80%), whereas with straw, humic acids predominated (82% of HS).