| In recent decades,the pollution of rivers has become more and more serious,which has gradually threatened our lives.The sediment is the largest “sink” of pollutants in rivers,at the same time being the largest “source”,which possesses huge harm.With the country’s emphasis on ecological environmental protection,the treatment of water pollution has been increasingly strengthened,which bring river environment improvement,but the large amount of pollutants in the sediment are still a huge hidden danger,and there are more and more treatment measures and methods to river sediments.Traditional methods of sediment pollution control,such as physical methods,chemical methods and bio-ecological methods,have certain applicability,but also possess high cost.Considering the increasingly prominent energy crisis,more energy-saving,effective and applicable treatment methods have aroused great focus in the treatment of river sediments today.Sediment microbial fuel cells(SMFC),a technology developed in the past decade,can effectively remove some pollutants from sediments by the effect of microorganisms and electrochemical systems,but there are still some difficulties in its application in natural water.The conditions for large-area applications are not mature enough.This paper mainly studied the influence of electrode pretreatment methods on sediment microbial fuel cells,and applied it to the treatment of chromium in the sediment,finally,the impact of tubificidae,a worm which widely exists in natural water,on the application of sediment microbial fuel cells in natural water was studied,so that we could continuously strengthen understanding and application of sediment microbial fuel cells to sediment pollution control.This paper first discussed the effects of different pretreatment methods on the startup time and electrochemical performance of sediment microbial fuel cells,and selected the appropriate electrode pretreatment method.Then,the SMFC were made using the electrodes processed by this method so that the removal effect and removal mechanism of chromium(VI)in the sediment by SMFC could be investigated.Finally,after the tubificidae was added to the SMFC anode,the influence of tubificidae on the water quality,sediment quality,electrochemical performance and anode microbial community of SMFC were studied.The main results are as follows:(1)Compared with untreated,CTAB treatment and pyrolysis treatment,the molten salt treatment and hydrochloric acid treatment have improved the surface properties of the electrode,and the molten salt treatment not only introduced N element into the electrode but also converted it to N-containing functional group,and the hydrochloric acid treatment increased the specific surface area and pore diameter of the electrode while introducing N element into the electrode material.The improvement of these surface properties made the start-up time of SMFC significantly shortened,which were made using the electrodes treated by molten salt treated and hydrochloric acid,what’s more,the maximum output power density of the SMFC whose cathode were treated by molten salt and hydrochloric acid were higher than that of the untreated SMFC with 25% and 11.1% improvement,which is very advantageous for the application of SMFC,but considering the little difference in SMFC performance caused by the two methods and hydrochloric acid treatment was simple and feasible,hydrochloric acid treatment was preferred as the electrode pretreatment method.(2)The SMFC were made using the electrodes treated by hydrochloric acid and placed in the sediment containing chromium(VI).After being operated for 60 days,it could be observed that the carbon brush which possesses larger specific surface area than carbon felt as a cathode could made the removal rate of chromium increased,and the external resistance of 1000 ohms was favorable for the removal of Cr relative to the external resistance of 100 ohms.When the cathode was made by carbon brush and the external resistance was 1000 ohms,the removal rate of chromium in the sediment was the highest,being 27.4%,while the cathode was made by carbon felt and the external resistance was 100 ohms,the removal rate of chromium in the sediment was only 10.5%,however which were greater than the removal rate of chromium in the sediment under natural conditions.According to the results of energy dispersive spectrometer analysis for SMFC anode and X-ray photoelectron spectroscopy analysis for SMFC cathode,it could be seen that the removal of chromium in the sediment mainly occurred on the cathode,the main mechanism of which was that chromium(VI)was reduced to chromium(III)on the cathode first,then to form chromium(III)precipitation to be removed.(3)The SMFC were made using the electrodes treated by hydrochloric acid.After the start-up of SMFC,tubificidae were added into the anode region.The devoured effect of tubificidae on organic matter in the sediment was beneficial for the removal of organic matter in the sediment,when coupled with SMFC,it could remove 28% of the organic matter in the sediment,which was higher than the removal rate of SMFC single effect and tubificidae single effect,which were 18% and 19%.However,the tubificidae also fed on the anode biofilm and inhibit some electrogenic bacteria such as Desulfobulbus,altered the structure of the anode microorganism,thereby reducing the electrochemical performance of the anode.At the same time,the biological disturbation effect of the tubificidae in the sediment would increase the concentration of ammonia nitrogen and COD in the overlying water,which deteriorated the overlying water quality,but the deterioration effect of the tubificidae on the overlying water can be offset by the purification effect of the SMFC.The cathode of SMFC was mainly utilized to purify the COD and ammonia nitrogen brought by the tubificidae,these pollutants could be used as nutrients for the cathode microorganisms,which was beneficial to the growth and reproduction of the cathode microorganisms and improved the electrochemical performance of cathode.In general,the overall electrochemical performance of SMFC was improved with the effect of tubificidae. |
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