The results based on 15N implied that earthworm feeding made a less contribution to the enhanced VSS reduction than earthworm–microorganism interaction, and the latter strategy was 3.81 times of the former (Table 3). The data supplied an complementary explanation why the previous studies about vermicompost or vermifilter highlighted the improvement of earthworm to microbial activity, but paid little attention to the contribution of
earthworm feeding to organic matter degradation. The previous study reported that the microbes are responsible
for the biochemical degradation of organic matter, whereas earthworms drive this process by conditioning the substrate and altering its biological activity in vermicomposting process [39].