Study On Purification Efficiency Of Electrolysis-Ecological Floating Bed(EC-EFB) For Eutrophic Water

Ecological floating bed（EFB）can not only continuously restore polluted water bodies,but also provide some ornamental value.However,the traditional ecological floating bed（T-EFB）has an unstable performance on nitrogen and phosphorus removal.In this study,the T-EFB and electrolysis-ecological floating bed（EC-EFB）were constructed,and the effects of current density,daily electrolysis time and high concentration of sulfamethoxazole（SMX）stress on the decontamination performance of T-EFB and EC-EFB were investigated.By study the physiological response of floating bed plants and the changes of biofilm components and microbial community structure on the surface of filler,the purification mechanism of EC-EFB was preliminarily explained.This study provides a new idea for the improvement of T-EFB,and also provides a certain theoretical basis for further application of EC-EFB.The main conclusions of this study are as follows:（1）Using volcanic rock or zeolite as the filler medium of EFB could improve the removal performance of nitrogen and organic matters,but little functioning in the removal of phosphorus.Meanwhile,zeolite is a better filler medium for EFB than volcanic rock.During the start-up stage,the content of polysaccharides and proteins in extracellular polymer substance（EPS）of T-EFB and EC-EFB were firstly increased and then decreased,and gradually stabilized.The polysaccharides content of biofilm in EC-EFB was significantly higher than that of T-EFB.Meanwhile,the amounts of microorganisms on the filler surface increased with the electricity acclimation process,and a certain electrolytic effect could significantly increase the number of microorganisms,but too high current density（2.02 m A/cm²）would inhibit the growth of microbes,resulting a decline of the microorganisms amounts on filler surface.（2）Compared with T-EFB,EC-EFB had a better nitrogen removal performance,and the increase of current density could significantly enhance the removal capacity of nitrogen pollutants of EC-EFB.However,increasing the electrolysis time would decrease the amounts of microorganisms,which was not conducive to nitrogen removal.EC-EFB could improve the phosphorus removal through electro-adsorption process,thus solving the problem of unstable phosphorus removal efficiency of T-EFB.Furthermore,results showed that the SMX stress had a great effect on the NO₃^--N removal in both T-EFB and EC-EFB,but could enhance the removal efficiency of TP and COD in EC-EFB.（3）The stress of high concentration of pollutants on plants can be alleviated under suitable electrolysis conditions,the content of malonaldehyde（MDA）and the activity of superoxide dismutase（SOD）in plant leaves were both reduced.The MDA content and SOD activity in EC-EFB were 6.08 nmol/g and 22.6 U/g when the electrolysis condition was 0.51 m A/cm²,24 h,which were significantly lower than those in T-EFB（38.64nmol/g and 26.13 U/g）.Meanwhile,electrolysis also significantly improved plant activity,the soluble protein content of plant leaves increased from 3.3 mg/g to 5.7 mg/g,but the chlorophyll content was decreased from 0.82 mg/g to 0.66 mg/g.（4）Electrolysis increased the water temperature by about 0.1～1.65℃,and also could help to the rapid recovery of dissolved oxygen（DO）in water,thus provides a suitable environment for the growth of bacteria in EC-EFB.In addition,electrolysis could greatly increase the load amounts of microorganisms on the surface of zeolite in EC-EFB.The results also showed that electrolysis significantly changed the microbial community structure,increased microbial richness,and promoted the proliferation of nitrogen functional bacteria such as Hydrogenophaga,Thermomonas,Deinococcus and Zoogloea.Furthermore,electrolysis could also promote the secretion of EPS by improving microbial activity,thus improving the nitrogen removal.Correlation analysis between microbial community structure and environmental factors showed that electrolysis could increase the abundance of Proteobacteria,Chloroflexi and Firmicutes,which was conducive to the nitrogen removal.（5）EC-EFB could remove pollutants by（electric）adsorption of fillers,utilization of plant roots,metabolism of microorganisms,and electrochemical oxidation/reduction process.NH₄⁺-N could adsorb quickly by the floating bed filler,and gradually oxidized to high-valence nitrogen such as nitrate nitrogen,which were finally removed by microbial denitrification,electrochemical reduction and direct absorption of plant roots.The electro-adsorption may the main process for the phosphorous removal in EC-EFB,which could prevent the phosphorous desorption from the fillers into water.Most of the organic matters were firstly adsorbed by the fillers and then participated in the denitrification process as electron donor,thus eventually being removed.