| Water is a complete ecosystem,including suspended substances,dissolved substances,sediment and aquatic organisms,etc.Therefore,during the process of water restoration,attention should be paid not only to the improvement of water quality,but also to the improvement of sediment and water ecology.Sediments are an important component of aquatic environment.As repositories of the overlying water body(e.g.,oceans,lakes,rivers,or reservoirs),sediments are usually composed of organic and inorganic materials and shelter a complex microbial ecosystem that thrives on several different electron donors and acceptors.So remediation techniques,which can accelerate the restoration rate are gaining importance globally.These methods include physical,chemical and biological processes.Microorganisms in sediments mediate several processes in the biogeochemical cycles of carbon,nutrients,metals,and sulfur.Microbial electrochemical systems(MESs)has many advantages in water and sediment restoration,and is worthy of further development and promotion.However,MESs application in water sediment restoration has problems such as performance degradation after system amplification and system configuration to be optimized,which limit its promotion and application.In this paper,the Benthic Microbial Electrochemical System(BMES)and Plant Microbial Electrochemical System(PMES)of different sizes were constructed for the purpose of MESs application in water body and sediment restoration,and the anode structure was optimized and the biological cathode was constructed.The three-dimensional structural anode was used in the BMES system and the efficiency of its application in water sediment restoration was analyzed.Build a pilot scale BMES system and investigate the effect of water sediment restoration.A more energy efficient PMES system was constructed by coupling plant and biological cathode.Based on the optimization of anode and cathode and the experience of pilot run,BMES was enlarged and used in the field experiment of water body restoration.The three-dimensional anode structure was firstly constructed and compared with the planar anode structure to investigate the influence of different structures of the anode,laying depth and laying area on the operating efficiency of the BMES system.The TOC content was all lower than 10 mg/L of the different anode structures,meeting the surface water environmental quality standards,indicating that the constructed BMES reactor could well control the water quality of the upper water body.The 3D fluorescence scanning results based on water quality showed that too small anode area was not conducive to the control of the humus content in the water in the reactor,and the anode with three-dimensional structure was conducive to the control of the release of humus substances in sediments to the upper water body so as to reduce the humus content in the water body.The removal efficiency of TOC and TN in the solid structure anode reactor was 20%?30%,higher than that in other reactors.It is found that the BMES system constructed by "3D anode" has obvious advantages in water quality,pollutant removal efficiency in sediment and power generation efficiency of the system in the process of water restoration.The BMES system was further amplified,and a 195?370 L laboratory pilot volume BMES system was constructed based on the "3D anode" to investigate its repair effect on water sediments.A 195 L reactor was constructed and a control reactor was set up to compare the removal effect of pollutants in water and sediments.Results the removal efficiency of BMES system was 1.2?1.6 times higher than that of the control reactor.The results demonstrated that BMES performed good in organic-matter degradation and energy generation from sediment and could be considered for river sediments in situ restoration as a novel method.Community analysis from the soil and anode using 16 S r DNA gene sequencing showed that more electrogenic functional bacteria was accumulated in anode area when circuit connected than control open circuit system.A benthic microbial electrochemical system(BMES)of 370 L was built for the bioremediation of river sediment.Synthesis wastewater with glucose was added to simulate the natural condition of Ashi River as an intermittent pollutant-holding water body and accelerate the removal of accumulated bio-refractory organic contents in sediment,represented by the concentration changes of polycyclic aromatic hydrocarbons,as the co-metabolic substrate for bacteria.The effluent TOC in the water layer of BMES was stabled at 40±2 mg/L and further reduced to 19±5 mg/L after the addition of synthesis wastewater,while the removal of polycyclic aromatic hydrocarbons(Benzo(b)fluoranthene,Benzo(k)fluoranthene and Benzo(a)pyrene)in sediment samples reaches 74%.A maximum power density of 63±3 m W/m~2 was achieved by BMES,which decreased due to cathode degradation and substrate limitation.The plant bio-electrochemical system(PBES)was constructed for organic pollutant removal and power generation.The bio-cathode,composed of granular activated carbon(GAC),stainless wire mesh and a plant species(Triticum aestivum L.),can catalyze cathodic reactions without any requirement for aeration or power input.During the 60-day-long operation,the average voltage of 516 m V and maximum power density(Pmax)of 0.83 W/m~3 values were obtained in the PMES.The total nitrogen removal and total organic carbon removal in PMES were 85% and 97%,respectively.Microbial community analyses indicated that power generation and organic removal associated bacteria were the predominant species of the bio-cathode,also plant growth promoting rhizobacteria were found in PMES.The results suggested that the plant coupled with GAC cathode may enhance the organic-matter degradation and energy generation from wastewater and therefore,contribute to a new method for bio-cathode design and energy-efficiency.Scale-up and insitu restoration tests were carried out in the last chapter.BMES system applied to in situ restoration of water bodies,and complete the removal of simulated water pollutants through the construction of biocathode ecological floating islands.The biological cathode was coupled with the ecological floating island,and the BMES system was constructed and operated in an outdoor pool of 8 m~3.The removal rate of COD was 61.90%,the removal of NH+4-N,NO-3-N,TN and TP were 63.26%,4.92%,5.79% and 39.26% respectively.The water quality in the system reached the standard of surface ? water quality.The maximum power density was detected to be 4.1 m W/m~2,and the polarization curve showed that the electrode potential of the cathode changed more significantly,and the anode performance was more stable.In this paper,the anode of the three-dimensional structure was used in the BMES system and its advantages are analyzed.A more energy-efficient PMES system was constructed by coupling plant with biocathode,and the mechanism of improving the performance of plant root secretions to bioelectrochemical systems was found and analyzed.Finally,BMES was enlarged and used in natural water bodies to obtain a more satisfactory operating effect.In short,MESs as a green technology provides the possibility for water body restoration. |
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