| The pollution caused by heavy metals,nitrogen and phosphorus has aroused wide concern,which have become one of the main environmental problems threatening ecological security and social development.Compared with traditional technologies,microbial electrochemical system(MES)has attracted extensive attention in water treatment due to its superiority in the simultaneous pollutants removal and energy recovery.With the aid of electric field between the anode and cathode of MES,charged ions in water can be driven to migrate directionally,achieving pollutants removal and recovery in a cost-effective way utilizing the chemical energy in the sewage,which provides a new route of MES in water treatment.This study aims to develop a novel MES utilizing the transport of elelctrons released by the oxidation of organics as driving force to deploy the directional migration of heavy metal,nitrogen and phosphorus ions in water,achieving high-efficient removal with low energy consumption.In this study,the system performance under different operation conditions were investigated,and the pollutants removal mechnisms were analyzed,in order to provide a theoretical support for the application of MES in the removal of inorganic pollutants with low concentration in water.The proposed microbial electrochemical heavy metal removal system enabled directional migration of Cu(?)and Cd(?)out from contaminated water driven by the electric field between the anode and cathode,and achieve final removal in the form as elementary state by cathodic electrodeposition or hydroxide precipitation in the cathode chamber.Firstly,a microbial electrochemical heavy metal electrodeposition system(MEMES)was developed,which obtained a maximum current density of 1.42±0.01A/m2 and a cathode potential of-0.70 V with an applied voltage of 0.8 V.The concentration of Cu(?)and Cd(?)decreased to less than 0.01 mg/L at 6 h and the removal efficiencies reached 98.8±1.0%and 98.2±1.1%for Cu(?)and Cd(?).It was proved by electrochemical analysis that the deposited products at the cathode promoted the electrochemical catalytic activity and lessened the internal resistance by 91%.The main product of Cu(?)was element Cu and a small amount of Cu2O,and the reduced product of Cd(?)was element Cd.Moreover,the microbial electrochemical heavy metal precipitation system(MEMPS)achieved the removal of Cu(?)and Cd(?)in the form as hydroxide precipitation taking advantage of the cathodic caustic without external energy input.The system achieved a maximum current density of 1.43±0.03 A/m2 at 20?,and removal efficiencies of Cu(?)and Cd(?)reached 98.6%.A 20-cycle operation demonstrates the long-term stability of the system,as the removals remained above 97.5%and the internal resistance was almost same.It was proved that Cu(?)and Cd(?)were removed in the form of Cu(OH)2 and Cd(OH)2 through the morphology characterization and element analysis of used cathode.A novel microalgae-microbial electrochemical system(MMES)was developed by the integration of Chlorella vulgaris into the cathode chamber,which employed the self-generated electric field to drive the directional migration of nitrogen and phosphorus ions,and achieve final removal by the synergistic effect of bacteria and Chlorella vulgaris.The photosynthesis of Chlorella released abundant dissolved oxygen and enahnced the current density output(2.0 A/m2),42.9%higher than that of the air-aerated control system.The removal efficiencies of NH4+-N,NO3–-N,and TP were 91.8±2.6%,90.6±2.1%,and94.4±1.2%,respectively.The capacity of MMES system for treatment of higher nutrients concentrations was further confirmed,as the system presented high nutrients removals(>86%)with increased initial nutrients concentrations.The analysis of microbial communities unraveled that abundant Geoalkalibacter and Thauera in the andic samples,which were electrochemical active and denitrify bacteria.The predominant bacteria in the cathodic samples were Thauera,Paracoccus,Azoarcus,and Labrenzia,which were related to nitrification and denitrification.Baed on the mass balance,88.4%of nitrate was removed by anodic denitrification process,and the removals of ammonia and phosphorus mainly relied on the assimilation by microalgae(69.3%and 76.0%,respectively).The microalgae-microbial electrochemical system(MMES)was used to achieve simultaneous removal of heavy metals,nitrogen and phosphorus ions in water.Oxygen was released by Chlorella vulgaris inoculated in the cathode chamber and used as electron acceptor,which significantly enahcned the output current density to 13.9±0.3 A/m3,33.7%higher than 10.4±0.2 A/m3 of air-aerated control system.The removal efficiencies for Cu(?),Cd(?),NH4+-N,NO3–-N,and TP were 99.0±0.2%,99.0±0.3%,89.8±1.3%,85.0±0.6%and 87.2±1.1%,respectively.The high concentration of dissolved oxygen and migrated heavy metals in the cathode resulted in abiotic stress on Chlorella vulgaris,thus reactive oxygen species(ROS)levels increased by 3.4 times.Moreover,the activities of main antioxidant enzymes increased to maintain cell activity.After operation,the surface of Chlorella vulgaris attached some precipitations,of which the main components were Cu(OH)2?Cd(OH)2.The FITR spectra showed that the C-O and?C-H bond were shifted.These results indicated that the removal process of heavy metals included cathodic hydroxide precipitation and adsorption by Chlorella vulgaris,and the removal of nutrients was mainly finished by bacteria(mainly nitrogen conversion related bacteria)and Chlorella vulgaris. |
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