Screening of lignin-degrading fungi and bioaugmentation on the directional humification of garden waste composting

The effective lignin-degrading strains mesophilic Sordaria tomentoalba (MSDA1) and thermophilic Thermomyces lanuginosus (HDGA2) were screened and used for the directional humification of garden waste (GW) composting. The strains MSDA1 and HDGA2 demonstrated significant Laccase (Lac), Lignin peroxidase (LiP), and Manganese peroxidase (MnP) activities, of which MnP activity was the highest at 746.31 U/L and 901.48 U/L, respectively. The composting BA-1 group was inoculated with the fungi MSDA1, HDGA2, M1 (mesophilic cellulose-degrading strain Aspergillus oryzae), and ZJ3 (thermophilic cellulose-degrading strain Thermoascus aurantiacus) on day 0, while BA-2 group was inoculated with the fungi MSDA1 and M1 on day 0 and the fungi HDGA2 and ZJ3 on day 3, respectively. The attained humic acid (HA) was 122.2 g/kg and 131.81 g/kg in BA-1 and BA-2 groups, respectively, significantly higher than the control group (72.97 g/kg). The organic matter contents of BA-2 (51.28%) were higher than that of CK (30.55%) and BA-1 (22.04%), and HA/fulvic acid (FA) were 1.26 (CK), 2.04 (BA-1) and 3.10 (BA-2), respectively. The results revealed that bioaugmentation could promote the directional humification by providing more FA precursors with the addition of lignocellulosic degradation fungi. Ammonium nitrogen (NH4+−N) could be fixed by FA during the high-temperature period, promoting NH4+−N being assimilated into amino acids and then converted to HA. Bioaugmentation effectively increased the HA and N content of the compost. The sequential addition of mesophilic and thermophilic fungi improved the quality of the directional humification compost.