Performance and stratified microbial community of vermi-filter affected by Acorus calamus and Epipremnum aureum during recycling of concentrated excess sludge

Vermi-filter combined with wetland plant (VFP) is an eco-friendly and sustainable approach for recycling of excess sludge by joint action of earthworms, wetland plants and microorganisms. However, the effects of wetland plants on sludge decomposition and involved microorganisms are remain unclear. This study investigated the effects of wetland plants on the treatment performance of VFP for concentrated excess sludge and microbial community distribution inside the VFP. The wetland plants' species of Acorus calamus and Epipremnum aureum were separately planted on the surface layer of vermi-reactors by earthworms Eisenia fetida. Results showed that the growth rate of E. fetida in VFPs significantly (P < 0.001) increased by 75%, compared to VF. In addition, the removal rates of total solids and chemical oxygen demand in VFPs could reach 61%-79% and 36%-68%, respectively, displaying a better performance of sludge reduction than in the VF. The surface layer of VFPs was a hotspot for degradation of organic matter, where bacteria played an important role in bio-decomposition rather than eukaryotes. Moreover, wetland plants could significantly (P < 0.001) enrich the eukaryotic population, rather than bacterial population. Compared to the VF, the wetland plants could promote the diversities of bacterial community in VFPs, showing specific functioned genus in different layers. In contrast, A. calamus could be a better candidate than E. aureum in the VFP. This study suggests that the inoculation of wetland plants can improve the performance for treating concentrated excess sludge by changing the biomass of earthworms and the structure of microbial community within the VFP. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The combination of wetland plants and vermi-filter can improve the treatment performance of excess sludge by enhancing the growth of earthworms and influencing the diversity of microbial community. Wetland plants play a crucial role in organic matter degradation and promoting biodiversity in the VFP system.