Effect And Mechanism Of The Stabilization Of Concentrated Excess Sludge By Vermi-filter Combined With Wetland Plant

As an end product after sewage treatment,excess sludge has a high content of water,harmful substances and unstable organic component,which are difficult to degrade.At the same time,excess sludge are rich in nitrogen,phosphorus,potassium and other nutrients required by plants and microorganisms.The treatment and resource utilization of excess sludge of urban and rural sewage treatment plants in China have always been an urgent problem,due to the duality features of excess sludge.As ecological friendly technology,vermi-filter and constructed wetland have been widely used in sewage and sludge treatment.But,they have the problems of low treatment efficiency and easy clogging.Taking into account the complementary features,vermi-filter combined with wetland plant?VFMs?are constructed for recycling of the excess sludge.The objectives of present study were to assess the performance and effect mechanism of VFMs for treating the concentrated sludge,prove the feasibility of its operation in small urban and rural sewage treatment plants.To provide new technical ideas for excess sludge resource treatment.The findings are as follows.The Acorus calamus and Epipremnum aureum were chosen as test plants,constructed vermi-filter combined with wetland plant to treat the concentrated excess sludge.The effect of no plants was used as a control group.Experiment for 60 days.The results showed that the VFMs could significantly improve the sludge organic matter interception and degradation efficiency.The total solid?TS?reduction rate and chemical oxygen demand?COD?removal rate of VFMs could reach to 61%?77%and 36%?84%,respectively.And the effluent soluble chemical oxygen demand?SCOD?of VFMs was reduced by 5.33%?56.45%compared with no plant group.In addition,the total phosphorus?TP?removal rate of VFMs reached to 40.70%?89.02%,and the nitrate nitrogen?NO₃^--N?concentration in VFMs increased by 19%?40%compared with no plant group.Three-dimension excitation emission matrix fluorescence spectroscopy?3D-EEM?revealed that the presence of plants can promote the removal efficiency of soluble microbial by-product like and aromatic proteins.Further research found that the degradation of sludge organic matter in VFMS mainly occurred in 0?10 cm surface vermicompost layer,due to the number of bacteria and fungi in each group was significantly higher than that in 10?15 cm middle ceramsite layer?P<0.05?.And the fungi population in VFMs of vermicompost layer was significantly increased by 51.9%?52.8%compared with no plant group?P<0.05?.High-throughput sequencing results showed that the dominant genus of bacteria and fungi in no plant group and VFM with Acorus calamus and Epipremnum aureum were different.Indicating that the presence of plants can change the microbial community composition.The presence of plants can increase the alpha diversity of bacterial populations,and significantly change the beta diversity and functional flora composition of VFMs.The A.Calamus can be used as the preferred plant in VFMs compred with E.aureum.In the mechanism investigation part,the earthworm mucus,earthworm feces and plant root exudates were separately extracted.The separate addition group and mixed addition group with different add ratio of earthworm plant root exudates were set up to perform an aerobic and anaerobic alternating degradation experiment of excess sludge.Revealing the earthworm and plant exudates effect of excess sludge degradation.Results showed that,earthworm and plant exudates could significantly promote TS reduction rate.The individual addition of earthworm mucus increased the total organic carbon?TOC?concentration by 13.03%?39.79%compared with the other groups.At the same time,the bacteria and fungi population in earthworm mucus individual added group significantly increased by 38.98%?98.63%compared with other groups?P<0.05?.Thereby promote the removal efficiency of soluble microbial by-products and aromatic protein substances.In addition,the individual addition of earthworm feces could promote the removal rate of TP.The TP removal rate of earthworm feces individual added group increased by 0.71%?5.46%compared with the other groups.The 3D-EEM results revealed that the addition of earthworm feces is beneficial to remove the fulvic acids from the extracellular polymeric substances?EPS?tightly bound layer of excess sludge.And the interactive of earthworm and plant exudates could effectively reduce the aromatic protein substances content of excess sludge EPS tightly bound layer.Compared with plant exudates,earthworm mucus and earthworm feces play an important role in the degradation of excess sludge organic matter.