Research On The Performances,Mechanisms And Application Of Mes Coupled With Ecological Bed For Restoration Of Water Bodies

It is essential to remediate the polluted urban river,which not only affected human body’s senses,but also endangers the aquatic creatures and human’s health.Compared with traditional physical and chemical technologies,bio-ecological remediation technology has the advantages of low cost and sustainability,but its development and application are also limited due to long treatment time,large area occupancy and difficult plant harvesting.Microbial electrochemical system as an emerging technology can provide new solutions to these problems through electronic compensation.In this paper,the microbial electrochemical system coupled with ecological bed was proposed.The enhanced pollutants removal efficiency and mechanism of the coupling system were discussed,Moreover,the amplification and engineering application were completed to provide a new paradigm for ecological remediation urban water.This paper focused on the ecological remediation of contaminated surface water.A novel MES coupled with ecological submerged bed（ECOSB-MES）was developed.The enhanced performance of fiber materials（basalt fiber and carbon fiber）in ECOSB reactor was compared.Combined with material characterization,pollutants removal effect and microbial analysis,it was concluded that carbon fiber had a larger specific surface area,better hydrophilicity and higher surface charge,so that the microbial biomass on its surface and the content of polysaccharides and proteins in the extracellular polymer were more,which enhanced the removal of pollutants.Then the MES was coupled with the ECOSB added carbon fiber,and three systems consisted of the coupled system（ECOSB-MES）,the ecological submerged bed（ECOSB）and the ecological submerged bed coupled with open-circuit MES（ECOSB-OMES）were constructed.The rate coefficient k of NO₃^––N degradation in ECOSB-MES was 1.6 and 1.8 times higher than that in ECOSB-OMES and ECOSB.The results of chlorophyll,protein and superoxide dismutase（SOD）in ECOSB-MES were 27.3%,44.3%and 12.9%higher than those in ECOSB.It was indicated that MES could increase the diversity and total number of microorganisms.It was showed that electroactive bacteria on anode like Desulfobulbus could promote the aerobic oxidation process of organic matter and release electrons to compensate cathode,meanwhile,cathode could enrich more species of functional bacteria like Rhodobacter,Pirellula,Hyphomicrobium,Thauera,which had a synergistic effect on oxygen reduction,nitrogen removal and plant growth.The synergistic effect of functional bacteria could enhance the removal of pollutants.On the basis of lab-scale ECOSB-MES configuration,the amplification experiment was carried out to compare and analyze the effectiveness of the scale-up ECOSB-MES in treating actual water under different states（open circuit,closed circuit and no plant state）.The intensive removal mechanism of pollutants under closed circuit state was also revealed.The scale-up ECOSB-MES was operated for 96 days from June to September.The maximum COD,TN and TP removal loads in closed circuit were 34.0 g/（m²·d）,2.2 g/（m²·d）and0.16 g/（m²·d）,respectively,which was 2.7,2.4 and 2 times higher than that of open circuit.Correlation analysis results showed that both plants and MES affected the removal of organic matter in water,and plants and MES were the key factors for phosphorus and nitrogen removal,respectively.Low temperature could inhibit denitrification and phosphorus removal processes in coupled system.The anode could oxidize humic-like organics in the water and release electrons to compensate the biocathode for oxygen and nitrate reduction.Functional bacteria such as electroactive bacteria,denitrifier bacteria,decarbonizing bacteria and phosphor-accumulating bacteria（such as Arthrobacter,Geobacter,Nitrospira,Arenimonas,Thiobacillus,Rhodobacter and Hyphomicrobium）were enriched in the scale-up coupling system.They could enhance the removal of pollutants through synergistic action.Based on the ECOSB-MES,a microbial electrochemical system coupled with ecological floating bed（ECOFB-MES）with the advantages of better practicability and landscape effect was developed for the simultaneous remediation of polluted surface water and sediment.By comparing the operation effects of ecological floating bed（ECOFB）,open-circuit MES coupled with ecological floating bed（ECOFB-OMES）and close-circuit MES coupled with ecological floating bed（ECOFB-MES）,the strengthening efficiency of the coupled system was investigated,and the interaction mechanism of plant,microorganism and MES was clarified.The maximum removal loads of COD,TN and TP in the coupled system were 48.2g/（m²·d）,3.4g/（m²·d）and 0.24g/（m²·d）,which were 1.4,8.5 and 1.5 times higher than those of the ECOFB.Nitrogen and phosphorus uptake by emergent plants in coupled system accounted for 6.0%and 14.0%,respectively.MES could improve the total number of microbial species and community diversity in the same system.The electroactive bacteria on the anode could promote the aerobic oxidation of organic matter and release electrons to compensate to the cathode for the reduction of oxygen,which created a lower dissolved oxygen environment to promote the denitrification process,so as to realize the synchronous removal of pollutants in the sediment and water.Chemoheterotrophic bacteria,aerobic denitrifying bacteria,phosphorus accumulating bacteria,rhizobia and other functional bacteria in coupled system could enhance the pollutants removal,reduce the stress effect of pollutants on plants,promote plant growth and generate bioelectricity through synergistic interaction.Based on the above theoretical and technical research basis,a ECOFB-MES engineering application was constructed in Guangxi Zhuang Autonomous Region,China for the in-situ remediation of an 8040 m² black and smelly artificial lake.The enhancement efficiency and mechanism of ECOFB-MES for simultaneous restoration of sediment and water body were verified under the application scale.During the one-year operation period,the concentrations of COD,NH₄⁺–N,NO₃^––N and TP could reach above the surface Class IV standards.The removal loads of COD,TN and TP in closed-circuit state were72.47 g/（m²·d）,4.26 g/（m²·d）and 0.39 g/（m²·d）respectively,which were 3.6,15.3 and 2.8 times higher than those in open-circuit state.The average TC removal rate of the sediment near the anode was 36.7%,which was 2.4 times higher than that of the sediment far from anode（15.5%）.The mean current of MESs increased from 0.6±0.1 m A to 32.0±2.9 m A with the gradual decrease of external resistance.The MES enhanced the total number of species and the bacteria diversity of polyester fibers and roots in the same coupled system.The dominant functional bacteria such as Pseudomonas,Gemmobacter,Aeromonas and Arthrobacter beneficial for oxygen reduction and nitrogen removal were found on biocathode,and this indicated that biocathode of present system could reduce nitrate mainly through heterotrophic nitrification and aerobic denitrification.This paper completed the laboratory research,system amplification and engineering application,which provided a new paradigm for the application of microbial electrochemical system coupled ecological bed in the field of in-situ remediation of urban water bodies.