Optimization And Application Of Bioelectrochemical Systems For In-Situ Remediation Of Polluted River Sediments

River is an important part of the earth’s ecosystem.With the rapid development of urban industrialization in China,a large number of industrial wastewater and domestic sewage discharged into urban rivers.The accumulation of a large amount of pollutants in the sediment of the river has become an important reason for the continuous pollution of the overlying water body,which poses a great threat to the living environment and health of the residents.Effective and practical remediation technology is an important way to accelerate the decontamination of polluted rivers.Bioelectrochemical system is a new type of environmental energy technology,which can produce electric energy in the process of accelerating the degradation of pollutants.By means of electrochemical workstation,gas/mass spectrometry,confocal microscope and high throughput sequencing,the bioelectrochemical characteristics of two important bioelectrochemical systems,sediment microbial fuel cell(SMFC)and Sediment microbiological electrochemistry snorkel(SMES)were compared,and the key factors affecting electricity production and sediment remediation performance were analyzed and optimized.On the basis of this,a pilot experiment(SMFC),which integrates in situ enhanced remediation and energy reuse,was constructed in a polluted river in the Pearl River Delta.The main research contents and conclusions are as follows:1.SMFC is more suitable than SMES for in situ remediation of contaminated sediments.Compared with SMES,SMFC can not only generate a power output of 10.7mW/m~2,but also increase the efficiency of degradation of persistent organic pollutant(SMFC)by 28.23%.Further analysis shows that the biofilm formed on the anode surface of SMFC has strong electrochemical activity and respiration(oxygen consumption)rate,while the electrochemical activeity of SMES biofilm is weak,and the electric voltage is only 20%-30%of that of SMFC.These results indicate that although both SMFC and SMES are bioelectrochemical systems,the enrichment of functional microorganisms and their biodegradation efficiency of PAHs are significantly different.SMFC is more suitable for further optimization and application as sediment remediation techniques.2.Sun light exposure has inhibitory effect on the PAHs degradation and electricity production of SMFC.Light exposure inhibited the power generation and output of SMFC at the start-up stage,but had no significant effect at the later stage.Accordingly,the overall degradation efficiency of SMFC was higher than that of SMES under light protection,but the specific enhanced degradation effect of benzo fluoranthene and benzopyrene in irradiated SMFC was probably due to the enrichment of special functional bacteria by anodic potential.Laser confocal microscope analysis showed that the biofilm of cathode was denser and the biomass was larger under illumination.The activity staining showed that most of the active functional microorganisms were distributed in the surface layer of the biofilm,but the inner layer was low in activity.The electrical properties of photo-cathode biofilms were stable under different illumination conditions,while the voltage of normal cathode biofilms decreased slightly linght-exposure condition.The results showed that the degradation and electrical properties of SMFC will be slightly inhibited by sunlight irradiation,and it should be paid attention to avoid sunlight in practical application.3.It is found that the number of electron-collecting wires can enhance the SMFC performance.The electrical performance of SMFC can be improved by increasing the number of wires of cathode or anode,and the improvment is more remarkable when the number of conductors increases at cathode.The lower the concentration of sulfides and reductive iron in the sediment near the conductors,the stronger the microbial function.The cathode biomass and the electrochemical activity of biofilm were also negatively correlated with the distance of lead.These results indicate that the reduced respiratory activity of the electrode causes the SMFC electrode to be unable to make full use of electrons,and a simple increase in the number of collector conductors may be an effective way to break through the performance of SMFC.4.On the basis of the optimization of laboratory test equipment,the SMFC in-situ test was carried out in a polluted river of fishery aquaculture wastewater in Pearl River Delta.The water temperature ranges from 6-25°C,SMFC output voltage in the range of0.84-0.95 V,and the maximum power density is 0.017 W/m~2.In situ pilot-scale study shows that SMFC can be used as an integrated equipment for sediment remediation and power generation in the Pearl River Delta region.The innovative and scientific significance of this study is reflected in the following three aspects:1)The enhanced remediation performance of SMFC and SMES to polluted sediments is compared for the first time.2)For the first time,the effects of light on the performance of SMFC were evaluated for the selection of more efficient and applicable bioremediation technologies.3)There was a gradient distribution of physicochemical characteristics in the biofilms on the surface of SMFC anode or cathode along with the distance to the wire,which may be the key factor to inhibit the improvement of SMFC scale-up.It is also proposed that increasing the number of collector conductors can greatly improve the performance of SMFC,which is expected to be an important progress in promoting the application of SMFC in the field of remediation of contaminated sediments and bioelectric energy recovery.