| Due to its ecological coordination,economy and applicability,traditional ecological floating bed is widely used in the ecology restoration of urban river water.However,because the floating bed mainly relies on the purification effect of plants and microorganisms,there are many problems such as weak water purification capacity,limited treatment efficiency which is related to low temperature conditions in winte.Besides,it’s difficult for plants to survive in heavily polluted water bodie.That result in poor purification effect of deep water bodies,which is hard to achieve effective restorastion of polluted water bodies.To this end,based on the characteristics of stable,high-efficiency and easy maintenance of electrochemical precipitation technique,the electrolysis technology was coupled with the ecological floating bed,and the biomass charcoal was used as the filler to construct a new type of electrolysis-ecological floating bed(E-FB)to purify the heavily polluted water body.The mechanism and products of NH3-N,NO3--N and PO43--P in floating bed cleaning and the mechanism of algae inhibition were discussed.At the same time,the effects of electrochemical parameters and environmental factors such as anode,electrolysis time,current density and temperature on the removal efficiency of nitrogen and phosphorus nutrients were studied to obtain optimized process parameters.On the basis of electrolysis-ecological floating bed,aeration technology was further added to strengthen the removal of NH3N in heavily polluted water,and the effects of aeration and electrolysis coupling on the purification efficiency of nutrients in water and the effects on biochar fillers,floating bed plants and microbial communities were further studied.The main conclusions were as follows:Electrolytic-ecological floating bed introduces electrolysis reaction into traditional floating bed,Mg2+ was produced by electrolytic magnesium anode to provide magnesium source,then combined with OH-produced by electrolyzed water to form Mg(OH)2 flocculant.The floc adsorbed a large amount of phosphate,algae and impurities in the water then precipitated,which inhibited the growth of cyanobacteria and increased the transparency of the water.At the same time,Mg2+,NH4+and PO43reacted to form a small amount of magnesium ammonium phosphate precipitate or magnesium phosphate precipitate,which can achieve efficient removal of NH3-N and PO43--P.The nitrate removal rate in the electrolysis-ecological floating bed treatment group was significantly improved by the electrochemical reduction of the cathode and the action of hydrogenotrophic denitrifying bacteria near the cathode.The electrolysis-ecological floating bed has a great influence on the nitrogen and phosphorus purification efficiency due to the anode type,and the most efficient method is to use iron anode for phosphorus removal.However,due to the consumption of a large amount of dissolved oxygen in the oxidation process of Fe2+,the removal of NH3N was suppressed.The nitrogen and phosphorus purification efficiency of the titanium anode was also less efficient.In contrast,the use of magnesium anodes was cheap,efficient and less energy consumed.By increasing the current density and prolonging the electrolysis time,the phosphorus removal rate of E-FB could be greatly enhanced,but there was no significant influence on the purification efficiency of NH3-N.Therefore,the practical application should consider the purification efficiency and energy consumption to save operation.The test results under different temperature conditions showed that E-FB can maintain high purification efficiency of nitrogen and phosphorus in low temperature environment,and it is suitable for popular use to rivers in low temperature or cold regions.Aeration-electrolytic enhanced ecological floating bed(A-EFB)was used in continuous flow simulation for purification of river water.The results showed that the addition of aeration unit in the electro-ecological floating bed system can effectively enhance the removal of NH3-N and TN.However,,there wad no significant effect on the removal rate of phosphate(P>0.05).Under the conditions of current density=0.58 mA/cm2,aeration rate=8 L/min,carbon to water ratio=1:25,HRT=3 d,when the influent concentration of NH3-N was 10 mg/L,TN was 12 mg/L and PO43--P was 0.8 mg/L,the purification efficiency of A-EFB for NH3-N could reach about 90%,the removal rate of TN was kept at about 42%,and the removal rate of PO43--P was 45%.Compared with traditional floating bed(FB)and electro-ecological floating bed(E-FB),NH3-N removal rate respectively increased by 78%and 66%,TN removal rate increased by 18%and 10%,the phosphate removal rate was 38%higher than that of FB,and there was no significant difference from the E-FB phosphorus removal rate.The results of physiological and biochemical indexes of Iris pseudacorus L.showed that the electrolysis reaction would have a stress effect on the growth and development of the floating bed plant,resulting in decreased chlorophyll content,increased SOD activity and MDA content,in addition,yellowing and dryness of plant leaves.However,the use of aeration technology could effectively improve the water environment,the dissolved oxygen in A-EFB was kept at 8 mg/L,the pH was lowered to below 8.5,and the ORP has raised to 160 mV.Compared with plants in E-FB,the average leaf length increased by 16.63 cm,the fresh weight increased by 9.51 g,and the chlorophyll content increased by 1.1 mg/g.Aeration alleviated the toxic effects of electrolytic reactions and high concentrations of NH3-N on aquatic plants,thereby accelerated the growth of aquatic plants.16S rDNA sequencing results on the bacterial community structure of A-EFB,EFB and FB filler surface showed that there were high relative abundance of characteristic denitrifying bacteria in both E-FB and A-EFB.Affected by electrolysis,the richness and diversity of E-FB bacterial communities were reduced,but electrolysis will produce H2 as an electron donor,which promoted the growth of hydrogen autotrophic denitrifying bacteria.A large number of dominant denitrifying bacteria family(Xanthomonadaceae,Comamonadaceae and Rhodocyclaceae)and hydrogen autotrophic denitrifying bacteria genus(Hydrogenophaga,Dechloromonas,Flavobactrium,Azoarcus and Anaerorhabdus)were enriched on the surface of E-FB fillers.Hydrogenophaga was the first dominant community in E-FB(38.56%),9.71%in A-EFB,and less than 0.5%in FB.The surface of A-EFB matrix was enriched with a large number of Nitrospira and Nitrosomonas genus,which accelerated the nitrification process and strengthens the removal of NH3-N in water by A-EFB.Acinetobacter also has a high abundance in A-EFB,and some of them have been reported to have good denitrifying phosphorus removal.By using biochar as floating bed filler,the growth of the biofilm on the surface and the adsorption of nitrogen and phosphorus had no significant effect on the pore structure,and could effectively save energy consumption of the electrolysis reaction.The energy consumption for purification of NH3-N and TP was initially calculated to be at least 0.18 kWh/g for NH3-N and 0.20 kWh/g for TP.During the electrolysis,Mg2+and Al3+were used to modify the biomass char in situ,which enhanced the adsorption of nitrogen and phosphorus.A reducing microenvironment with anaerobic,high pH and slightly higher temperature was formed inside the electrolysis-ecological floating bed filler,which was beneficial to the denitrification process and thus improved the denitrification capacity. |
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