| The eutrophication were caused by the high concentration of nitrogen in the water.When the concentration of nitrate in the groundwater or drinking water exceeded the standard,it posed a threat to human health.The biological denitrification has been widely used because of its high efficiency,low cost and low secondary pollution.The novel biological denitrification,especially the discovery of heterotrophic nitrification-aerobic denitrification bacteria,has made the simultaneous nitrification and denitrification come true,which leaded it to becoming a research hotspot in the field of nitrogen removal.However,the C/N ratio in these treatment processes was relatively high,generally above 8.While much wastewater,especially groundwater or drinking water,always contained only a small amount of carbon source.Therefore,it is an urgency to find an effective method for treating wastewater with low C/N ratio.The development of bioelectrochemical system(BES)has made it become simple for treating the the wastewater with low C/N ratio due to the electrons could be obtained from the cathodic electrodes via external circuit,and it compensated for the disadvantages of the lack of carbon source in biological denitrification.Considering that organic matter in BES is a provider of energy and ammonia nitrogen can be used as a potential electron donor,organic wastewater containing ammonia nitrogen was used as the anodic electrolyte,and the heterotrophic nitrifying microorganisms were used as anodic inoculants in this work.The treatment of wastewater with low C/N ratio was operated in the cathode by the advantages of cathodic electrochemical reduction in BES,and because of the diffusion and migration of ammonia nitrogen from anode to cathode,heterotrophic denitrifying bacteria capable of simultaneous nitrification was selected as the inoculant bacteria.In this study,a bacterial consortium,named as MAS,was enriched from the activated sludge in coking plant and it was used as the anodic inoculum.The heterotrophic denitrification strain Acinetobacter sp.Y1 isolated by our laboratory was used as the cathodic inoculum.The biocathode BESs were constructed to study the performance of denitrification and electricity generation under different low C/N ratios and investigated the condition control and influencing factors at low cathodic C/N ratio.It not only provided the treatment of organic wastewater containing ammonia nitrogen,but also provided theoretical basis for denitrification of wastewater with low C/N ratio.The biocathode MFC was used as the research object to study the denitrification in cathode and the electricity generation performance under different cathodic C/N ratios.The experimental results showed that when the cathodic C/N ratios were 8 and 2,the nitrate degradation rate were 98.77% and 83.21%,respectively,which improved about 31% and 63% than the culture conditions in the erlenmeyer flasks.It indicated that the denitrification efficiency was increased through bio-electrochemical coupling in cathode.At the same time,it was the first time for heterotrophic nitrification-aerobic denitrifier Y1 to be used in MFC,and it proved that the strain Y1 could obtain electrons from the carbon brush electrode and the treatment of wastewater with low C/N ratio by electrochemical denitrification in MFC became a reality.The biocathode M3 C was used as the research object to research the denitrification in under different cathodic control potentials at the low cathodic C/N ratio of 2.The results were as follows:(1)There was a wide range of control potentials,and the denitrification coule be promoted during the range from-0.1 to +0.1 V(vs.SCE);(2)The optimal cathodic control potential was-0.1 V(vs.SCE),and the maximum degradation ratio and removal rate of nitrate were 98.28% and 49.70 mg/L/d in cathode,respectively.Compared with the control group where the cathode did not control the potential,the removal rate has increased by 3.7 times.The accumulation of nitrite nitrogen in cathode reached the maximum on the first day and then rapidly decreased to almost 0.The biocathode MFC was used as the research object to investigate factors that affected the degradation characteristics and electricity generation performance of MFC systems at the low cathodic C/N ratio of 2.The results were as follows:(1)Scanning electron micrographs and degradation results showed that the different methods of bacterial domestication have a greater impact on the startup of the MFC systems.(2)The optimal external resistance was 1000 ?.The maximum removal efficiency and rate of nitrate nitrogen were 83.61% and 83.96 mg/L/d within one day respectively.The maximum removal percentages of COD in anode and total ammonia nitrogen in MFC system were 92.43% and 76.68% respectively.(3)The best substrates for cathode and anode were sodium citrate and sodium acetate respectively and the total internal resistance was minimum.The maximum removal efficiency and rate of nitrate nitrogen were 99% and 87.71 mg/L/d respectively.The maximum removal percentages of COD in anode and the total ammonia nitrogen in MFC system were 96.51% and 88.21% respectively.(4)Conductive materials experiments showed that it was beneficial to improve the degradation efficiency and electricity generation performance by filling the cathodic and the anodic chambers with conductive materials.The highest removal ratio and rate of nitrate nitrogen were 99.99% and 99.36 mg/L/d respectively.The maximum removal percentages of COD in anode and total ammonia nitrogen in MFC system were 97.0% and 95.81% respectively.Moreover,the effect of filling the conductive material in anode was better than that of the filling in cathode. |
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