| Water resources shortage and water pollution have become global issues that restrict the economic and social development of countries.Comprehensive prevention and control of water pollution has always been valued by the national government and environmental protection agencies.In terms of water pollution prevention and control,activated sludge technology has developed into the most widely used sewage biological treatment technology.However,there is still the problem of excessive nitrogen and phosphorus and gaseous pollution in the tail water.Constructed wetland(CW)is an ecological wastewater treatment technology composed of plants,substrates,and microorganisms which widely used in urban and rural sewage treatment,especially in improving the water quality of sewage treatment plant effluent has a good prospect for development because of its low energy consumption and easy management.Insufficient oxygen supply is identified as one of the major factors limiting organic pollutant and nitrogen(N)removal in CW.Based on above discussion,In this study,a novel aerated CW using waste gas from biological wastewater treatment was developed,and the pollutant removal mechanism and microbial community in the novel CW were analyzed.Subsequently,the coupling of partial nitrification(PN)and aerated CW system was designed,and analyzed the feasibility of using CW to reduce nitrous oxide(N2O)during PN process.The migration-conversion-degradation characteristics of pollutant during removal process were also investigated.N2O reduction mechanism of PN-CW system was determined by microbial analysis.The main research conclusions are as follows:1.This study designed a novel aerated vertical flow constructed wetland(VFCW)using waste gas from biological wastewater treatment systems to enhance overall wetland treatment performance and eliminate waste gas pollution during biological wastewater treatment processes.Compared with unaerated VFCW,the introduction of waste gas significantly improved NH4+-N and TN removal efficiencies by 128.48 ±3.13%and 59.09 ± 2.26%,respectively.Compared with the unaerated VFCW,aeration with waste gas improved the chlorophyll content 40.7±2.2%suggesting that aeration would remarkably improve plant growth.Furthermore,the waste gas ingredients,including H2S,NH3,greenhouse gas(N2O)and microbial aerosols,were remarkably reduced after passing through the VFCW.The removal efficiencies of H2S,NH3 and N2O were 77.78 ± 3.46%,52.17 ± 2.53%,and 87.40 ± 3.89%,respectively.In addition,the bacterial and fungal aerosols in waste gas were effectively removed with removal efficiencies of 42.72 ± 3.21%and 47.89 ± 2.82%,respectively.The results show that the oxygen enrichment of the waste gas enhances the water purification effect of the constructed wetland,and the risk of pollution of the exhaust gas is eliminated through the filtration and purification of the constructed wetland.VFCW can be regarded as a biological filter,and the tail gas can be purified through matrix absorption,water dissolution and microbial degradation.The effect of simultaneous purification of water and gas is achieved,which has significant technical advantages and application prospects.2.Aeration can change the removal and migration pathway of nitrogen and phosphorus in wetlands.The removal of nitrogen from traditional wetlands mainly depends on the adsorption and accumulation of substrate.The airflow within the exposed air wetland reduces the adsorption of the substrate,but the substrate nitrogen fixation in the tail gas wetland is not affected.Obviously weakened due to the accumulation of more microorganisms in the substate of waste wetlands.Phosphorus removal is mainly due to the adsorption and accumulation of substrate in wetlands,followed by plant absorption.The effects of nitrogen and phosphorus absorption in plants in aerated wetland systems are significantly higher than in non-aerated wetland systems because aeration enhances plant growth.In addition,The VFCW intermittently aerated with waste gas not only optimized the DO distribution but also improved microbial abundance and diversity due to the introduction of microbes from the SBR by aerating with waste gas.The abundance of nitrifying bacteria(AOB,NOB)and denitrifying bacteria in VFCW intermittently aerated with waste gas was 6.3 and 2.6 times that of control wetlands,respectively.Furthermore,intermittent aeration with waste gas markedly enhanced the abundance of total bacterial abundance in the sediment which was 3.6 times that of control wetlands.The VFCW intermittently aerated with waste gas and the SBR had the highest percentage of shared OTUs(19.70%).This result verified that the highest microbial abundance in VFCW intermittently aerated with waste gas was from the SBR through the introduction of waste gas.3.Sweet flag expressed different responses and levels of tolerance to nitrite stress.When exposed to 30 mg/L of nitrite,physiological protection systems in sweet flag were triggered to maintain normal plant growth.Especially,when nitrite concentration was at 40 mg/L,obvious physiological changes in sweet flag were observed,which displayed significant increase in the percentages of electrolyte leakage,malondialdehyde(MDA),antioxidant enzymes activity(T-SOD?POD and CAT)and proline,obvious decrease in the chlorophyll content and plant height suggesting sweet flag was badly damaged.Therefore,for CWs with sweet flag,30 mg/L is the recommended threshold value for nitrite.The NAR of reactor was increased from 43.38%to 52.88%by reducing the stirring time during the aerobic stage.The relative amounts of AOB and NOB in the reactor sludge were analyzed by FISH.The results showed that the AOB and NOB in the sludge accounted for the total number of bacteria 78.48%and 13.83%,respectively,indicating that AOB was gradually enriched,while NOB was slowly eluted in the reactor.Therefore,reducing the stirring time during the aerobic stage can effectively achieve a stable partial nitrification(PN)process.The coupling of PN and aerated CW system was constructed.It was found that the concentration of NO2--N from the PN effluent was reduced from 17.07±1.54 mg/L to 0.34±0.18 mg/L,indicating PN effluent can be deeply treated under the aeration wetland operation mode to eliminate the risk of high nitrite pollution.4.N2O during PN process was remarkably reduced after passing through the VFCW.The removal efficiency of N2O were 88.72±2.39%,indicating that the CW can be used as a purification measure for N2O in PN waste gas.N2O reduction mechanism of PN-CW system was studied by quantitative polymerase chain reaction(qPCR)technology and high-throughput sequencing,and found that the waste gas wetland could significantly change the microbial community structure.The abundance of bacteria related to nitrogen metabolism and total bacteria increased significantly,thus accelerating the conversion of nitrogen.Meanwhile,the density of nosZ gene copies increased significantly,thus the expression of nosZ gene was accelerated. |
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