The Research On Application And Scaling-Up Of Sediment Microbial Fuel Cells For Freshwater Lake Treatment And Remediation

With the accelerating urbanization process in China,the economic prosperity and development have also brought a series of environmental problems.The eutrophication treatment and remediation of freshwater lakes is one of the key research topics in recent years.As an important"internal source"of pollutants in the surface water environment,sediments maintain a continuous exchange of both materials and energy with the overlying water,and the releases of nutrients such as nitrogen and phosphorus are the main limiting factors for lake eutrophication.In this context,Sediment Microbial Fuel Cells（SMFC）,as a novel green water treatment technology,can use organic matter in sediment as substrates to produce electricity while remove nitrogen and suppress phosphorus in the overlying water at the sediment-water interface and inhibit methane production.This study takes a eutrophic freshwater lake as the research subject and uses SMFC for its treatment and remediation.The objective is to verify the engineering feasibility of the technology applied to in-situ treatment of lakes,investigate its performance of electricity production under different configurations and scales,examine its inhibitory effect on the release of pollutants such as nitrogen,phosphorus and methane,analyze its effect on the microbial community in sediment,and predict its risk of releasing secondary pollution in the process of lake treatment and remediation.The main research contents and results are as follow:（1）The dual-chamber SMFC reactors using freshwater lake sediment as the anode substrates had the capability of long-term operation and stable power production.The open circuit potential of the system could be basically stabilized at about 635 m V,and the maximum output power could reach 7.51×10^-3 m W.The SMFC system had a good effect of nitrogen removal and phosphate suppression.The removal and suppression rates of ammonia nitrogen and phosphate in the anodic overlying water could reach71.3%and 65.4%,respectively.The methanogenic activity of sediment could be inhibited by SMFC under closed circuit operation.The methane concentration of the reactor in open circuit operation could be up to 300 times of that in closed circuit operation,but the effect of external resistance on its methanogenic inhibition effect was not significant.The biofilm attached to the anode of the reactor after long-term operation was mainly dominated by Proteobacteria and Desulfobacterota.Methanogenic bacteria of the Halobacterota phylum was the dominant archaea,and their abundance was lower in the closed-circuit group.A potential difference of about100 to 200 m V could exist between the top and bottom electrodes of the isolated multi-layer anodes under open-circuit operation when the deep span in the sediment was large.（2）The single-chamber SMFC pilot system had good and stable outdoor operation performance when the cathode was not frozen.The maximum open circuit potential and maximum output power could reach 941.3 m V and 0.556 m W,respectively.The output voltage decreased with decreasing cathode area.Folded cathodes could promote higher output voltage,and a twice-folded cathode increased the system output power by approximately 5.7 times.The system internal resistance of the outdoor SMFC unit was slightly higher in winter than in summer.After long-term outdoor experiments,the stainless-steel electrodes showed good corrosion resistance and could be suitable for practical applications.The single-chamber SMFC inhibited the release of ammonia nitrogen,phosphate and total organic carbon in the overlying water by 31.1%,73.6%and 21.9%,respectively,compared to the blank group.The methane concentration of the open-circuit group could be 8.5 times higher than that of the closed-circuit group.（3）The system performance was significantly affected by seasonal changes and dissolved oxygen concentration in the water column.With the increase of dissolved oxygen at the sediment-water interface of the anode and the decrease in the water layer of the cathode causing the decrease of output voltage.The effect of SMFC on the concentration of nitrogen and phosphorus in the surface water of the lake was not significant,but it caused a small increase in nitrate nitrogen and a decrease in ammonia nitrogen concentration in the overlying water above the sediment-water interface.The SMFC inhibited ammonia nitrogen and phosphate above the sediment by 55.1%and46.8%,respectively,during the stable phase of summer operation.The distribution of bacterial communities in the sediment near the anode at the bottom of the lake was not significantly different except for Caldisericum.For archaea,the methanogenic bacteria Methanosaeta and Methanoregula of the Halobacterota phylum showed dominance at all sites,while their relative abundance at the blank sites（22.11%and 20.29%）was higher than that at the SMFC sites（15%-18%）.（4）The substrate turnover rate of SMFCs applied to freshwater lakes was directly proportional to the scale and output power,with 0.0014,0.0830 and 1.9463 mmol/d acetate equivalent for laboratory,pilot and lake-scale SMFC,respectively,when using the same sediment and electrode materials.When eutrophic freshwater lakes are targeted,attention should be paid to limiting its substrate turnover rate to prevent secondary pollution release from excessive and rapid decomposition of sediment organic matter while ensuring sufficient performance output of the SMFC device.Under the assumption that the SMFC anode acts at a depth of 5 cm,SMFC can effectively suppress nitrogen and phosphorus release from the sediment to overlying water with an output power density of no more than 1 m W/m~2.