Study On Light Packing Constructed Wetland-electrochemical Nitrogen And Phosphorus Removal System For Tail Water Of Wastewater Treatment Plant

With the completion and operation of a large number of urban sewage treatment plants in China,the amount of nitrogen and phosphorus carried by the tail water of sewage treatment plants is increasing day by day,which poses a serious threat to the water environment.In view of the carbon source bottleneck of deep nitrogen removal from tail water of sewage treatment plant,the technology of light packing constructed wetland-electrolytic deep nitrogen and phosphorus removal from sewage plant tail water was developed.The effects of cathode number,inoculation mode and flow direction on the construction of the light packing constructed wetland-electric phosphorus and nitrogen removal microbial system were studied systematically.The effects of residence time,current density and temperature on the efficiency of deep phosphorus and nitrogen removal of the system were investigated,and the key operating parameters of the system were obtained.The phosphorus removal path of the light packing constructed wetland-electrolysis system was studied by infrared spectroscopy,and the dominant functional bacteria and microbial action mechanism of the system were explored by using 16s r RNA Amplicon high-throughput sequencing technology.The main conclusions of the study are as follows:The number of cathodes,inoculation mode and flow direction had significant effects on the construction of the light packing constructed wetland-electrolytic nitrogen and phosphorus removal system.With the increase of the number of cathodes,the phosphorus and nitrogen removal efficiency of the system was improved,and the NO₃^--N removal rates of single cathode,double cathode and triple cathode system were72.54%,67.02%and 97.73%,respectively.The removal rates of TN were 57.25%,53.24%and 80.86%,respectively.the removal rates of PO₄^3--P were 78.13%,81.2%and85.52%,respectively.The phosphorus and nitrogen removal efficiency of the inoculated sludge system was higher than that of the inoculated sludge system.The removal rates of NO₃^--N,TN and PO₄^3--P of the inoculated sludge system and natural biofilm system were 97.73%and 60.29%,80.86%and 46.72%,85.52%and 66.80%,respectively.The downward flow reactor is beneficial to the construction of phosphorus and nitrogen removal system.The removal rates of NO₃^--N,TN and PO₄^3--P in the down flow reactor were 52.34%,53.1%and 25.27%higher than those in the up flow reactor.Residence time,current density and temperature had significant effects on nitrogen removal efficiency of the light packing constructed wetland-electrolysis system,but had no significant effect on phosphorus removal.With the increase of residence time,current density and temperature,the denitrification effect of the system was improved.The removal rates of NO₃^--N,TN and PO₄^3--P were 95.40%,88.20%and 96.94%,respectively when the temperature was 28℃,the residence time was 3 h and the current density was 0.05m A/cm².Systematic infrared spectroscopy showed that the main ways of phosphorus removal in the system were the precipitation of iron ion and PO₄^3--P,the adsorption of Fe（OH）₃colloid and Fe O（OH）,and the flocculation of iron-phosphorus polymerization.The results of 16s rRNA analysis in the light packing constructed wetland-electrochemical system showed that the function bacteria of anode were:unclassified Gallionellaceae（22.9%）and Dechloromonas（13.5%）.These two kinds of bacteria belong to Proteobacteria,which can remove NO₃^--N by Fe²⁺.The function bacteria of cathodic were:Anaerolineaceae（7.7%）,Thiobacillus（5.9%）,Clostridium＿sensu＿stricto＿1（5.0%）,Desulfuromonas（3.7%）,unclassified Desulfuromonadales（3.6%）Desulfomicrobium（2.8%）,Limnobacter（2.8%）.A large number of sulfate reducing bacteria（include:Desulfobulbus（0.3%）,Desulfomicrobium（2.8%）,Desulfovibrio（0.2%）,Desulfuromonas（3.7%）and unclassified Desulfuromonadales（1.0%））and sulfur autotrophic denitrifying bacteria（include:Thiobacillus（5.9%）and Limnobacter（2.8%））were enriched in the cathode,which indicated that the sulfur cycle played an important role in the removal of nitrogen in the system.