| Phosphorus is one of the core elements of life activities,and it is also an element which is easy to cause eutrophication.Constructed wetlands can romoval the phosphorus by the adsorption and precipitation of the substrate,the absorption and transformation of plants,and the assimilation of microorganisms,and it has been widely used in recent years.At present,the research on phosphorus migration and transformation in constructed wetland mainly focused on inorganic phosphorus and organic phosphate s,in which phosphorus is at+5 valence state.However,recent studies have found that the role of phosphine(PH3)in the phosphorus cycle of wetland can not be ignored.The research on PH3 in constructed wetlands is of great significance to improve the biochemical cycle of phosphorus in constructed wetlands and promote the long-term stable operation of constructed wetlandsField monitoring and lab simulation methods were used in this study.Based on the field investigation of two actual wetlands,the release flux of gaseous PH3 was obtained,the vertical distribution of PH3 in wetland substrate was explored,and the correlation between PH3 and environmental factors was analyzed.The main conclusions were as follows(1)A method for analysis and detection of phosphine in constructed wetland was established.A trace PH3 detection system based on secondary cold trap preconcentration and gas chromatography equipted flame thermal ion detector(FTD)was built,and the stable test of gaseous PH3 was realized.The detection limit of this phosphine analysis system was about 1×10-13(v/v),and the relative standard deviation(RSD)was 4.8%.The digestion device of matrix bound phosphine(MBP)was designed,and the sample weight,digestion temperature,digestion time and other conditions were optimized.The extraction and anglysis method of dissolved PH3 in wetland was put forward,and the stable analysis of PH3 in water,gas and solid phase of constructed wetland was realized.(2)Clarified the distribution characteristics and influencing factors of phosphorus in actual wetlands.It was found that MBP content of river wetland was 57.85 ng/kg,which was significantly higher than that of coastal wetland(29.08 ng/kg).The PH3 in the wetland substrate mainly showed a trend of high in the middle layer,low in the surface layer and bottom layer.The person correlation analysis showed that Resin-P was the main factor affected the production of PH3,salinity was not significant.The microbial community structure of the wetland was analyzed,and it was found that the production of PH3 had a significant positive correlation with Thiobacillus and Achalaplasma which suggested that phosphine may be produced in the process of sulfate reduction.(3)The production characteristics of phosphine of constructed wetland system and its effect on phosphorus removal was explored.After the four groups of subsurface flow constructed wetland system stably,the concentration of dissolved PH3 in the effluent was in the range of 2.68～4.77 μg·L-1,and the MBP content was in the range of 4.02~118.65 ng/kg.The release flux of gaseous PH3 was observed in the later stage of a typical cycle,and the release flux was in the range of 127.96～220.50 pg-m-2.h-1.The removal of phosphorus in constructed wetland system mainly depended on the adsorption and precipitation of substrate The contribution of gaseous PH3 release to phosphorus removal was very small.The dissolved PH3 accounted for 0.09～0.20%of phosphorus removal pathways.This part of PH3 was discharged from the wetland system with effluent,and then dissipated into the atmosphere or transformed into other forms of phosphorus.(4)The mechanism of phosphine production in constructed wetland was analyzed.The formation of PH3 in constructed wetland system was due to phosphate reduction by microorganisms under anaerobic conditions.Lactic acid did not directly participate in the reduction of phosphate,but indirectly promoted the production of NADH,thus assisted microorganisms in phosphate reduction to produce PH3. |
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