| With the rapid development of economy,the expansion of industry and agriculture,and the growing population,a large amount of industrial wastewater and domestic sewage discharged into rivers and lakes,resulting in organic,nitrogen,phosphorus and heavy metal pollution.Sediment and overlying water in rivers and lakes continue exhanging material and energy.Under certain conditions,contaminants in sediments can release into overlying water by desorption and diffusion.Therefore,in order to eliminate water pollution by the roots,sediment treatment must be carried out,but traditional sediment remediation technologies have certain limitations.According to the present situation of water pollution and the transformation of pollutants combining with the microbial electrochemical technology,SMFC(sediment microbial fuel cell),which can be used for enhanced remediation of water body was constructed.The effects of different factors were studied and the optimal structure and operating conditions were determined.On the basis of optimal structure and operating conditions,different SMFC reactors were compared with the natural degradation to study the enhaced effect and electrical performance.The results showed that SMFC could promote the degradation of organic matter and PCBs in sediments.After an operation period of 60 d,the maximum removal rates of TOC and DOC in sediments were 48.45±1.52% and 62.23±1.70%,respectively.The maximum removal rate of PCBs at the initial concentration of 57.2±1.5mg/kg was 14.66±0.61%,which was about 2.3 times that of open circuit condition.The removal of organic matter and PCBs in sediments made the concentrations of pollutants in overlying water obviously lower than that of open circuit condition.The maximum voltages from the SMFC for organic matter and PCBs removal were 0.768 and 0.581 V,and the maximum power densities were 98.99 and 60.79W/m2,respectively.The remediation of water body polluted by heavy metals showed that SMFC while promoting the degradation of organic matter in the sediment can make Cr,Cu and Cd transform to a more stable form,which is the residue form,and the cathode under anoxic conditions can effect ively promote the removal of Cr(VI)and Cu(II)in overlying water.After 60 d operation,Cr(VI)and Cu(II)removal rates in overlying water were 88.5±3.5% and 82.1±3.2%,the maximum voltage and power density were 0.517 V and 54.21 m W/m2.The study of SMFC enhancing nitrogen removal showed that SMFC had a significant effect on the removal of nitrate nitrogen in overlying water and sediment interstitial water.When the initial concentration of ammonia nitrogen was 30mg/L,the concentration was reduced to less than 5mg/L after 30 d operation,and the concentration of TOC in sediment and overlying water can be removed with the maximum voltage of 0.539 V and the maximum power density of 66.34 m W/m2.The study of sediment property changes showed,SMFC can promote the biological polymer,fulvic acid and humic acid degradation,and change the p H and conductivity,lower the UV254 of sediment dissolved organic matter,and increase the humification degree of sediment organic matter.It was found that ferric oxide and nonionic surfactant(Twain-80)could enhance the removal of pollutants in sediments.The combined effect of Fe(III)and SMFC can make the removal rates of TOC and DOC in sediment to be 2.64 and 1.82 times of open circuit condition,and the concentration of Fe(III)oxide decreased with the reaction time.Twain-80,as nonionic surfactants can make the hydrophobic organic contaminants in sediment to be dissolved.When the mass ratio of Twain-80 and PCBs was 50,the concentration of PCBs in sediment interstitial water was nearly 10 times of the blank.The removal rate of combined application was 58.67±2.02%,which was about 2 times of SMFC and 6 times of natural degradation.Microbiological mechanism of pollution remediation and electricity generation by SMFC showed the rich microbial communities in both of the sediment and the anode biofilm.The electrode as the electron acceptor made a relative high abundance of electricigen.The production of electricity and the degradation of organic matter occurred simultaneously,and the TOC removal rate of the sediments with different organic matter contents were positively correlated with the power output.Different functional groups of microorganisms were related to the degradation and transformation of the corresponding pollutants.Samples of Clostridium,Bacteroides,Pseudomonas and Shewanella fermentation of bacteria and Geobacter electricigen can participate in the completely degradation of organic matter.The relative abundance of Clostridium,Longilinea and Bradyrhizobium in samples involved in PCBs degradation increased.In the pathway of transformation of heavy metals,the produced electron by the degradation of organic matter were transferred to cathode,Cr(VI)and Cu(II)as the final electron acceptors can reduce their concentrations in the overlying water,and the mass balance of heavy metals in SMFC proved the various ways of their transformation.In the process of nitrogen removal by SMFC,the aerobic nitrifying bacteria in the overlying water oxidized NH3 to NO3-and then diffused into the sediments,and the relative abundance of Pseudomonas and Bacillus(denitrifying bacteria)in sediment were significantly increased.Using NO3-as the final electron acceptor,N2 was produced by reduction reaction,the denitrifying bacteria take advantage of the electrons produced by organic matter degradation to achieve the simultaneous removal of organic matter and nitrogen removal.The selective effect of environmental conditions on microbial community structure was obvious.The comparative analysis shows that SMFC is a kind of microbial electrochemical remediation technology for engineering application with simple structure,easy operation,no secondary pollution,high efficiency of pollutant removal and power generation.SMFC can be enhanced by certain methods to improve the processing efficiency,which is an economical,efficient and environmental friendly technology for surface water pollution remediation. |
PDF Full Text Request