| Anthropogenic Greenhouse Gas（GHGs）emission control is one of crucial missions human need to face.Is there any risk of GHGs emission increasing during wastewater treatment and other processes?How to reduce GHGs emission from pollution control processes?Such problems of pollution swapping raised concern of environmentalists.In recent years,as an ecological treatment facility,Constructed Wetlands（CWs）widely applied in non-point source pollution control,water environment quality improvement and also wastewater treatment areas.In consideration of diversified environmental conditions and correlative physical,chemical,biological and ecological processes,it is significant and representative to choose CWs as research objective to analyse GHGs emission process and control strategies.Therefore,this research choose the most common CWs type,free water surface flow（FWS）,to proceed gas sample collecting,testing and data analysis.Three main kinds of GHGs including CH4 ,CO2 and N2O emission models are established based on testing results to clarify the releasing characteristics,and also the GHGs emission control strategies research.The primary research conclusions are as follows:（1）A pilot scale CWs including FWS series receiving polluted river water was chosen to proceed GHGs sampling and detection research work for one year.Three main kinds of GHGs samples from different seasons were collected.The results showed that the emission flux range of CH4 ,CO2 and N2O were-0.12～4.06,-101.13～2370.93and-0.08～0.11 mg m-2h-1respectively,and corresponding average fluxes were 0.65,330.54,and 0.02 mg m-2h-1respectively.The seasonal divergence of CH4 and CO2 fluxes were obviously.CH4 flux were high at summer and autumn and CO2 flux were high at spring and summer.Both of CH4 and CO2 flux were quite low at winter.（2）The GHGs emission models for CWs-FWS were established based on GHGs model of soil science,and parameter setting was reset according to the features of carbon and nitrogen concentrated,and strong reductive environment of CWs-FWS.The CH4 emission model simulated the main methane generation and consumption processes including methanogens degrading BOD,slowly decomposable organic materials and rhizodeposition processes,and also methanotroph consuming CH4 process.CO2 emission model based on the combined action of autotrophic respiration from wetland plants and heterotrophic respiration from microorganisms.N2O model simulated the N2O and N2generation from biological denitrification process.Therefore,micro-ecological environment,Net Primary Productivity（NPP）,nitrate concentration of wetland sediments,and environmental conditions were significant influence factors for GHGs emission.（3）The CH4 ,CO2 and N2O emission models were calibrated and verified through monitored flux from the pilot scale CWs-FWS.The results showed the simulated and tested conclusion have preferable congruency,but the congruency were different among seasons.The congruency were high in winter and spring for CH4 emission when flux were low;The highest congruency is CO2 model which indicate the plant autotrophic respiration as the dominate role for CO2 model was feasible;N2O emission was quite relevant with the degree of carbon scarcity（C:N of wetland inflow）.Organic substance was not limited factor for denitrification process when C:N was high.Then N2O can act as alternative electron acceptor when NO3-was in short supply,result in abundant of N2O were reduce to N2 and lower final N2O flux.The GHGs emission model for CWs-FWS could simulate satisfactory the releasing process for each gas.However,further improvements were necessary for GHGs model of CWs-FWS such a complex ecological system.（4）In order to control GHGs emission,the GHGs effect mitigation strategies were implemented according to model calculation and testing results.Wetland plant growth had significant influence on CWs whether on absorbing and releasing GHGs,or effects on microbial action.Therefore,plants administration especially plants regular harvesting was the primary strategy for GHGs effect control.On the other hand,microorganism population and functions affected pollution removal efficiency directly,and affected GHGs especially CH4 and N2O fluxes at the same time.Hence,the C:N of wetland inflow was one of vital strategies for GHGs emission control.The results of this research indicated the three kinds of GHGs releasing process was not only correlated with carbon and nitrogen cycle in ecological system of CWs-FWS,and also with pollutant composition of wetland inflow.Besides,the latter item will effect the former one to a great extent.Hence,synergistic control of wetland ecological environment and inflow conditions will improve the ecological function for CWs. |
