| With the construction of national ecological civilization and the enhancement of environmental protection consciousness,People have higher and higher requirements for the water environment.Advanced treatment of wastewater treatment plant(WWTP)effluent plays an important role in improving water environmental quality.As a typical ecological technology,constructed wetlands have many advantages such as ecology,environmental protection,low cost,energy saving and so on.It has broad application prospects in the advanced treatment of WWTP effluent.In the constructed wetland system,microorganisms are an important part of the constructed wetland,which undertake the degradation of most pollutants.Aerobic denitrifier is one of them,which can overcome the limitations of traditional anoxic denitrification process and can be used in denitrification under aerobic conditions.Bioaugmentation with aerobic denitrifier in denitrification of WWTP effluent has a wide application potential.In this study,pilot-scale Circuitous-flow constructed wetland was used as research object,and three operation modes of conventional Circuitous-flow constructed wetland,Circuitous-flow constructed wetland+Vertical-flow constructed wetland,High-speed circuitous-flow constructed wetland+penetrative constructed wetland were formed through reconstruction.The simulated stone revetment hardening channel was used as the control pool.In the summer and autumn,the removal of COD,NH4+-N,NO3--N,TN and TP from the effluent of a wastewater treatment plant in Suzhou was studied under the condition of 66h hydraulic retention time.At the same time,an aerobic denitrifier was screened and isolated from the wastewater of an aeration reaction tank of a WWTP in Suzhou,and the identification,growth characteristics and optimum conditions of the strain were studied.Finally,the screened aerobic denitrifier were expanded and cultured,they were added to the constructed wetland according to the dosage of 0.1mg/L of microbial inoculum.The removal effects of three batches of constructed wetland—non-inoculated batch(P1),inoculated batch(P2)and colonization batch(P3)—on conventional pollutants COD,NH4+-N,NO3--N,TN and TP in effluent,especially the denitrification effect,were studied,and the changes of microorganisms added to wetland water and substrate in the three batches were detected.The main research conclusions are as follows:(1)Advanced treatment of wastewater treatment plant(WWTP)effluent by Circuitous-flow constructed wetland of the three operation modes.In summer,the COD decreased to 5.63?9.66 mg/L,the removal rate reached 79.4?93.9%,and the COD values of the three wetlands reached Class ? surface water after 66 h of operation.TN decreased to 3.11?3.69 mg/L,the removal rate reached 28.92?31.07%;NO3--N decreased to 2.21?2.98 mg/L,the removal rate reached 29.9?43.6%.In autumn,After the hydraulic retention time was extended to 66 h,the COD decreased to 10.30-17.07 mg/L,and the removal rate reached 58.67-74.81%.The COD value reached Class ??? surface water;TN decreased to 3.06-3.55 mg/L,and the removal rate reached 19.44?28.25%;NO3--N decreased to 2.58?2.94 mg/L,and the removal rate reached 18.9?27.6%.In summer and autumn,the removal efficiency of COD,NO3--N and TN in effluent was significantly higher than that of the control group which simulated stone revetment hardening channel.Under the condition that the concentration of conventional pollutants in the influent was not much different,the removal ability of wetlands in high temperature seasons was better than that in low temperature seasons.The WWTP had well removed NH4+-N and TP from the wastewater.The concentration of NH4+-N and TP in the effluent of the WWTP was extremely low in summer and autumn,with NH4+-N values ranging from 0.058?0.343 mg/L and TP values ranging from 0.0184?0.083 mg/L,near Class ? and Class ?surface water.Due to the extremely low concentration of NH4+-N and TP,it was difficult to evaluate the advantages and disadvantages performance of Circuitous-flow constructed wetland and control pool in the removal efficiency of NH4+-N and TP.(2)The removal of COD by three types of constructed wetlands in the same season was not different,After operation 66 h,it could reach the COD Class ? surface water in summer,and reached the COD Class ??? surface water in autumn.There were some differences in the removal of total nitrogen and nitrate nitrogen.The removal effect was in the order of High-speed circuitous-flow constructed wetland+penetrative constructed wetland>conventional Circuitous-flow constructed wetland>Circuitous-flow constructed wetland+Vertical-flow constructed wetland.The operation mode of High-speed circuitous-flow constructed wetland+penetrative constructed wetland had the best removal effect on total nitrogen and nitrate nitrogen,which was related to the filtering effect of wetland wall on water.(3)A strain of aerobic denitrifier H21 was screened from wastewater in aeration reaction tank of a WWTP in Suzhou.Based on 16S rDNA sequence analysis and colony morphology observation,H21 was identified as Achromobacter sp.Peripheral nitrate reductase subunit gene(napA)was amplified from H21.The single factor experiment showed that the optimal temperature for aerobic denitrification of H21 was 30?,the optimal C/N ratio was 10,the optimal rotation speed was 100 rpm,and the optimal initial pH was 7?8.Under the optimal conditions,H21 could remove 75.9%of nitrate nitrogen and 73.3%of TN,and had high denitrification performance.(4)Aerobic denitrifier Achromobacter sp.H21 was used to enhance denitrification on WWTP effluent.The experiment included three batches:non-inoculated batch(P1),inoculated batch(P2)and colonization batch(P3).Three batches of constructed wetland had a COD removal rate of P1 62.4%,P2 61.8%,and P3 67.5%,a TN removal rate of P1 32.9%,P2 43.2%,and P3 36.0%,and a NO3--N removal rate of P1 31.4%.,P2 45.2%and P3 38.6%.The removal ability of TN and NO3--N was P2>P3>P1,which indicated that the addition of aerobic denitrifier H21 had a certain effect on the removal of TN and nitrate in constructed wetlands.Through high-throughput sequencing,it could be concluded that the microbial community in water had the highest abundance,but its diversity was the lowest after adding microorganism.There was no such regularity in the substrate.In terms of relative abundance,the relative abundance of Achromobacter sp.in water was the largest after the P2 batch was added microorganism,the relative abundance value decreased after the end of P2(about 50%),and the relative abundance value after the end of P3 was higher than that at the end of P2.The relative abundance of Achromobacter sp.in the substrate was higher at the beginning of P2,and decreased sequentially at the end of P2 and P3,but maintained at a certain value,which indicated that aerobic denitrifier Achromobacter sp.H21 had a certain impact resistance in water and the substrate in denitrification of WWTP effluent. |
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