Tracking the composition and dominant components of the microbial community via polymerase chain reaction–denaturing gradient gel electrophoresis and fluorescence in situ hybridization during vermiconversion for liquid-state excess sludge stabilization

To quantitatively explore the microbial community modified by earthworms, a vermifilter (VF, with earthworms) and a conventional biofilter (BF, without earthworms) were continuously operated to stabilize excess sludge. The results demonstrated a positive role imposed by earthworms on compositions and dominant components of microbial community in the VF. For one thing, the phyla Actinobacteria and Acidobacteria were only detected in the VF, which might explain for the higher Shannon index of bacteria in the VF (H = 2.58) than that in the BF (H = 1.99). For another, the total proportion of dominant bacteria in the VF increased by 23% compared to the BF. Moreover, quantification analysis explicitly noted that the dominant bacteria in VF were β-proteobacteria (27 ± 2%) and γ-proteobacteria (24 ± 1%) while that in BF was Bacteroidetes (21 ± 1%). In conclusion, stimulated by earthworms, a unique microbial community developed in the VF, thus improving the stabilization of excess sludge.