Effect of earthworms on the performance and microbial communities of excess sludge treatment process in vermifilter

Previous studies have shown that the stabilization of excess sludge by vermifiltration can be improved significantly through the use of earthworms. To investigate the effect of earthworms on enhancing sludge stabilization during the vermifiltration process, a vermifilter (VF) with earthworms and a conventional biofilter (BF) without earthworms were compared. The sludge reduction capability of the VF was ∼85% higher than that of the BF. Specifically, elemental analysis indicated that earthworms enhanced the stabilization of organic matter. Furthermore, earthworm predation strongly regulated microbial biomass while improving microbial activity. Denaturing gradient gel electrophoresis (DGGE) analysis showed that the most abundant microbes in the VF biofilms and earthworm casts were Flavobacterium, Myroides, Sphingobacterium, and Myxococcales, all of which are known to be highly effective at degrading organic matter. These results indicate that earthworms can improve the stabilization of excess sludge during vermifiltration, and reveal the processes by which this is achieved.

► The vermifilter (VF) had higher sludge reduction ability than a biofilter (BF).
► Elemental analysis showed that earthworms enhanced the stabilization of excess sludge.
► Dehydrogenase activity in VF biofilms was much higher than that in the BF.
► Specific microbes in earthworm cast enhanced the degradation of organic matter.