| Swine wastewater contains high concentrations of organic matter typically.In some areas the discharge of swine wastewater accounts for more than industrial and domestic sewage,meanwhile it is one of the important source of agricultural non-point Source pollution in China.The rational disposal and utilization of resource potential of swine wastwater that has been the research difficulties and hot spots at home and abroad.In this research the constructed wetland?CW?-microbial fuel cell?MFC?system was built,which coupled the microbial fuel cell?MFC?characteristics of pollutant degradation and synchronous electricity generation and the structural advantage of constructed wetland.A novel integrated vertical flow constructed wetland?IVCW?-microbial fuel cell?MFC?was designed and structured firstly,that based on the traditional vertical flow constructed wetland?VFCW?-microbial fuel cell?MFC?and combined the advantage of the single flow direction in the structure.The swine wastwaster as the target substrate was fed to IVCW-MFC for the long-term continuous operation,the effectiveness of wastwater treatment and synchronous electricity generation performance of IVCW-MFC were enforced successfully.At the same time the main degradation pathway of target substrate and the influence mechanism and synergy of electricity generation performance were researched under the external conditions of the resistance to load shock,diurnal rhythm and the external resistance.The analyses of the structural characteristic,the operational factor and the bioelectrochemical performance were researched in the system long-term continuous operation process.The selection of different macrophytes and the response of root exudates to system performance were researched.The degradation and electricity generation mechanism of the swine wastwater in the coupled system was revealed.The main results of this study are as follows.?1?Running the VFCW-MFC and IVCW-MFC under the open-?VFCW-MFC-O?and close-circuit?VFCW-MFC-C?model respectively the best removal efficiency of pollutants were obtained when HRT was 2d.In VFCW-MFC-O the removal efficiency of COD and TN were 91.21%and 31.97%which were better than VFCW-MFC-C.And in VFCW-MFC-O the removal efficiency of NH4+-N was42.93%and better than the VFCW-MFC-C.But in IVCW-MFC all the removal efficiency of pollutants of IVCW-MFC-C were better than IVCW-MFC-O.The removal efficiency of COD,NH4+-N and TN were 98.75%,95.75%and 84.45%respectively.In the electricity generation performance the voltage output and the max power density of IVCW-MFC-C were better than VFCW-MFC-C.In IVCW-MFC-C the average voltage output in later was 542±43mV,the max power density was0.292W/m3,and the internal resistance was 495?.?2?Using the swine wastwaster as the target substrate fed to IVCW-MFC for the long-term continuous operation,the efficient degradation of pollutants and synchronous electricity generation IVCW-MFC were enforced successfully.In IVCW-MFC-C the removal efficiency of COD,NH4+-N,NO3--N and TP were79.65%,77.50%,75.13%and 55.07%respectively,which holed the better pollutant removal capacity than in IVCW-MFC-O.The main reasons were the electricity generation promoting the metabolism of microorganisms thus promoting the degradation of pollutants of IVCW-MFC-C.In IVCW-MFC-C long-term continuous operation process the range of voltage output varies from 598mV to 713m V,the max power density was 0.456 w/m3.During the operation period,a total of 7137 C of electric charge were produced,with an average of 6.74 C/d·L.in this study the output voltage and the max power density among these showed greater advantages than the studies of the similar structure CW.In IVCW-MFC-C the output voltage showed regular changes based on diurnal rhythm,and the output voltage during daytime was higher than nighttime.In IVCW-MFC-C the output voltage increased with the increasing of external resistance,and the removal efficiency of COD and NH4+-N declined slightly with the increasing of external resistance.?3?In IVCW-MFC the characteristics of microbial community structure was analyzed by a high-throughput sequencing analysis.The intrinsic relationship among degradation efficiency of pollutants,environmental temperature and microbial community structure was revealed.In IVCW-MFC-C the richness and evenness in the anode surface biofilm were higher than in IVCW-MFC-O.In the anode surface biofilm the relative abundance of Geobacter and Desulfuromonas were 17.87%and1.59%.In IVCW-MFC-C in the biofilm of anode,cathode and root the relative abundance of Proteobacteria were 43.01%,57.66%and 81.03%respectively,and of the relative abundance of Firmicutes were 25.02%,8.86%and 5.23%respectively.These two phyla occupied an absolute advantage in IVCW-MFC-C.The characteristics of microbial community structure was analyzed in IVCW-MFC-C long-term steadily operation process with the seasonal change.It was found that in IVCW-MFC-C the microorganisms successed with the seasonal change,and the dominant colonial structure was also quite different.In summer?higher temperature?the Shannon diversity index in the biofilm of anode and cathode was higher than in winter?lower temperature?.The richness and evenness of anode-the important reaction area of EAB?electrochemically active bacteria?in the electricity generation process,were higher in cathode.Proteobacteria occupied an advantage in both the seasons.In IVCW-MFC-C the EAB of different electricity generation characteristics with higher richness were detected contained Geobacter,Aeromonas and Clostridium in anode biofilm,and Pseudomonas in are-bio-cathode.But for the efficient degradation of pollutants in IVCW-MFC-C,Trichococcus,Thiobacillus,Hydrogenophaga,Exiguobacterium,Nitrospira,Citrobacter and Hyphomicrobium were detected.The relative abundance of Thiobacillus was higher in anode biofilm.The relative abundance of Hydrogenophaga was higher in root biofilm.The relative abundance of Exiguobacterium,Nitrospira,Citrobacter and Hyphomicrobium were higher in the cathode environment with enough O2,and realized their own enrichment by degradation pollutants.?4?In the study of the plants existence or not and the different plants in IVCW-MFC would bring the different performances.In the unplanted,Canna indica,Acorus calamus,and Ipomoea aquatica systems,the COD removal rates were 80.20%,88.07%,84.70%,and 82.20%,respectively,and the NH4+-N removal rates were49.96%,75.02%,70.25%,and 68.47%,respectively.The decontamination capability of the Canna indica system was better than those of the other systems.Plants played an important role in the pollutants removal,especially for the NH4+-N removal.Beside the existence of plants in IVCW-MFC-C could promote the efficiency of electricity generation.It was found that the different plants caused the different electricity generation performances.With the Ipomoea aquatica the electricity generation performance was promoted obviously,the output voltage was upto752±26mV,the max power density was 0.4964W/m3 and the internal resistance was417.5?.Because of the root oxygen secretion and root exudates from different plants roots,it would bring different effects to the pollutant removal and synchronous electricity generation.In the unplanted,Canna indica,Acorus calamus,and Ipomoea aquatica system the different root oxygen secretion impacted the DO concentration along the water flow,at a same sample the Canna indica team hold the highest DO.In the root secretory experiment had found that the species and quantity of root exudates and extracts from different plants were different,and it Influenced on the microbial flora structure.The amount and the rate of release were consistency of different matter in the root exudates and extracts,TP<TN<Polysaccharide<Amino acids<DOC.Comamonas,which has rarely been analysed in CW–MFC systems,was found to have a certain advantage in the anodes in this study.Cloacibacillus,which was detected in the anode,was found to be the core bacterium in a marsh gas tank and appeared in an anaerobic environment and under high COD concentration... |
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