Kinetics of organic matter removal and humification progress during sewage sludge composting

•Sewage sludge composting was conducted in aerated bioreactor.•OM degradation and HS and HA formation proceeded according 1. order kinetics.•Kinetic constant of OM degradation was 0.196d−1.•Kinetic constants of HS and HA formation were 0.044d−1 and 0.045d−1.•Humification occurred most intensively during the first 3months of composting. This study investigated the kinetics of organic matter (OM) removal and humification during composting of sewage sludge and lignocellulosic waste (wood chips, wheat straw, leaves) in an aerated bioreactor. Both OM degradation and humification (humic substances, HS, and humic acids, HA formation) proceeded according to 1. order kinetics. The rate constant of OM degradation was 0.196d−1, and the rate of OM degradation was 39.4mg/gOMd. The kinetic constants of HS and HA formation were 0.044d−1 and 0.045d−1, whereas the rates of HS and HA formation were 3.46mgC/gOMd and 3.24mgC/gOMd, respectively. The concentration profiles of HS and HA indicated that humification occurred most intensively during the first 3months of composting. The high content of HS (182mgC/gOM) in the final product indicated that the compost could be used in soil remediation as a source of HS for treating soils highly contaminated with heavy metals.