Effect Of Activated Phosphate Powder As Phosphorus Source On Nitrogen Removal From Secondary Effluent In Subsurface Flow Constructed Wetlands

With the increasingly serious eutrophication of water bodies,the discharge standards of nitrogen and phosphorus in urban sewage have been continuously improved,and the conventional sewage treatment technology can no longer meet the discharge standards of nitrogen and phosphorus in sewage.Constructed wetland as a economic and efficient ecological treatment technology has been in secondary sewage treatment plant is widely used in dealing with the depth of the nitrogen and phosphorus,in view of the conventional secondary processing have been added chemical phosphorus removal unit,most of the secondary sewage treatment plant appear"low phosphorus and high nitrogen"phenomenon,lead to artificial wetland phosphorus element in the already cannot satisfy the growth of plants and microbes.Most of the studies have focused on the supply of organic carbon in the denitrification and denitrification of constructed wetlands,while ignoring the important role of phosphorus source in the denitrification of constructed wetlands.Therefore,the active development of stable phosphorus source is of great significance to the promotion of the project to improve the nitrogen removal effect of constructed wetlands in the secondary effluent.This paper will be low grade phosphate rock powder after appropriate activation of lignite that are rich in humic acid as a slow release source of phosphorus,taking test apparatus are adopted to simulate the vertical,the undercurrent of artificial wetland,choose a reed as wetland plant,river sand as the main substrate,respectively,set with and without planting reeds wetland group in both groups,each group of four,two groups of wetland substrate in the activation of ground phosphate rock to add quantity and add consistent position.Inlet water quality was simulated for secondary effluent of urban sewage treatment plant with NO₃^--N as the main pollutant.The treatment effect of pollutants in each wetland system under different hydraulic retention time（HRT of1,3,5,7 d,respectively）indicated the stability of constructed wetland under different pollution loads.The operating period of constructed wetland is from July 7,2020 to September 20,2020.As the system is running for a short time,the influence of C/N and T on the test is not considered temporarily under the condition of ensuring sufficient carbon sources.During the operating period of the constructed wetland system,the effects of the wetland system with and without reed planting on pollutant treatment were compared and analyzed.At the end of the experiment,the growth conditions and chlorophyll fluorescence values of reed under different treatments in the reed planting artificial wetland group were analyzed,and the characteristics of substrate microorganisms in different wetland systems were further studied based on high-throughput sequencing technology.The main conclusions are as follows:（1）During operation,the results of pollutant removal by each wetland system showed that under different HRT,in the constructed wetland without reed-planting,adding activated phosphate powder had no significant removal effect on TN and NO₃^--N,although the removal effect of adding lignite system（LC1）was relatively good but not significant.In the wetland system without reed planting,the addition of activated phosphate powder not only had no significant effect on nitrogen removal,but significantly increased the TP concentration in the produced water（P<0.05）.However,the planted reed constructed wetland had significant effect on the removal of pollutants（P<0.05）,in which the activated phosphate powder group（PR-LC2）had the best removal effect on NO₃^--N when HRT was 5 days,and the average removal rate reached98.12%.When HRT was 5d and 7d,the removal effect of activated phosphate powder group（PR-LC2）on TN was the best and kept at about 95%.The average TP removal rate of PR-LC2 wetland system during the operation period was maintained at about90%without significant difference,and the effluent TP concentration was maintained at about 0.02mg/L.（2）The growth and chlorophyll fluorescence analysis showed that the plant height of PR-LC2 was significantly higher than that of the other three groups（P<0.05）,and the plant height of LC2 was the minimum.The fresh weight of PR2 and PR-LC2was higher than that of CK2 and LC2,and the fresh weight of PR-LC2 was significantly higher than that of PR2（P<0.05）.LC2 and PR-LC2 had the most developed roots,and the root dry weight of PR-LC2 was significantly higher than that of LC2（P<0.05）.In terms of chlorophyll fluorescence parameters,PR-LC2 Fv/Fm value was the highest.Y（Ⅱ）was not significantly different between PR2,LC2 and PR-LC2.The NPQ value of PR-LC2 was significantly higher than that of the other three groups（P<0.05）.（3）The results of high-throughput sequencing showed that proteobacteria was the most dominant phyla at the taxonomic level.The total relative abundance of CK1,PR1,LC1,PR-LC1 and CK2,PR2,LC2 and PR-LC2 were 40.98%,28.16%,42.15%,41.23 and 42.99%,64.70%,45.04%,45.13%,respectively.In the genus level,8 groups of artificial wetland,CK1,PR1,LC1,PR-LC1 and CK2,PR2,LC2,PR-LC2 matrix related to nitrogen and phosphorus species in total abundance were 18.40%,18.35%,22.91%,22.11%and 23.18%,25.41%,39.79%,37.74%,including soxhlet bacteria genera,pseudomonas and bacillus genus is the highest abundance of heterotrophic denitrifying bacteria genera,accounting for heterotrophic denitrifying bacteria genera and 65.2%～73.9%of total abundance,is one of the main artificial wetland denitrifying bacteria genera;Bacteria with aerobic denitrifying function were also detected,including Flavobacteria,Bacillus,Arthrobacter and Rhizobiaceae.The abundance of CK1,PR1,LC1,PR-LC1 and CK2,PR2,LC2 and PR-LC2 aerobic denitrifying bacteria were 0.37%,0.53%,1.02%,1.07%and 1.79%,1.41%,2.48%,2.74%in 8groups of constructed wetlands,respectively.Pseudomonas,Bacillus and Fusarium were also the main dephosphorization bacteria in constructed wetlands.The abundance of CK1,PR1,LC1,PR-LC1 and CK2,PR2,LC2 and PR-LC2 were 4.49%,7.97%,5.37%,8.75%and 3.10%,1.25%,1.09%,5.07%,respectively in 8 groups of constructed wetlands.