| In this study, the anaerobic digestion of swine wastewater was the treatment object. Bidens frondosa and Rumex dentatus, two special plants, were cultivated in the subsurface flow constructed wetland. Their roles on the wastewater purification effect were studied. We improved the internal structure of subsurface flow constructed wetland and installed4units of the wetland. Gravel and gray bricks were filled as principal media in the wetland. Purification effect and influence factors of different units for swine wastewater were comprehensively studied. Microbial diversity, nitrification and denitrification intensity, migration and removal efficiency of contaminants were analyzed along the wetland. The principal conclusions were concluded as follows:1. Both of Bidens frondosa and Rumex dentatus had good resistance to contaminants and strong ability of anti-shock loading. During the period of growth, Bidens frondosa could grow in the range of50～200mg·L-1NH4+-N, and the fastest rate of the growth occurred at about200mg·L-1NH4+-N. At ca.100mg·L-1of NH4+-N, Bidens frondosa had relative long growing period, stable removal efficiency and the highest accumulated N and P. Rumex dentatus could also grow in the range of50～200mg·L-1NH4+-N. However, the fastest growth rate, stable removal rate and the highest accumulated N and P carried out when the concentration of NH4+-N was at ca.150mg·L-1.2. At the stage of vigorous growth for Bidens frondosa and Rumex dentatus plant pot system, the average Total Nitrogen (TN) removal efficiency for the treated swine wastewater were87%and71%and the average Total Phosphorus (TP) removal efficiency arrived over75%for both systems. Compared with non-plant system for wastewater treatment, the estimated contributions of Bidens frondosa on TN and TP removal efficiency in swine wastewater were20%and11%, respectively. The estimated contributions of Rumex dentatus on TN and TP removal efficiency were up to17%and12%, respectively. 3. After80days’start-up for the subsurface flow constructed wetland system, the cultivated plants wetlands system entered a stable period about10days in advance than controlled wetlands (non-plant system). A positive linear relationship (r2>0.90) existed between the temperature and removal efficiency of COD, NH4+-N, TN and TP of waste water in wetland units.4. When HRT of system was4days and CODCr, NH4+-N, TN, TP concentrations in the influent were520,110,120,10mg·L-1, COD and TP in the treated swine wastewater was eliminated and removal efficiency arrived over60%,70%, respectively. The estimated contribution of plant for COD and TP removal efficiency were at around10%and3%. The impact of temperature was important for N removal by plants. The contribution of plant for ammonia and TN removal was up to13%and6%. Compared with the general subsurface flow constructed wetland, this system for the COD and TP removal efficiency increased about3to5%due to its improved internal structure and also has some positive impact on the ammonia and TN removal.5. The population of microorganism in the plant wetland was gradually decreased along the wetland. The population of microorganism at the front of wetland was1to2orders of magnitude more than the population at the end of the wetland. After stable operation of system, the population of microorganisms could fluctuate with seasonal alternation.6. A trend was observed that nitrification intensity decreased gradually from upper layer to lower layer, nitrification occurred mainly in the front of the wetland, and gradually decreased along the wetland. Spatial variation of denitrification intensity is not obvious. A trend was observed that denitrification intensity decreased slightly and maintained at relative high degree along the wetland. Nitrification intensity was around30mg·kg-1·d-1, but the denitrification intensity arrived at over240mg·kg-1·d-1. Therefore, the rate of denitrification is much higher than that of nitrification.7. A trend was concluded that the concentrations of COD and TP in plant wetlands were decreased gradually along the process, and the elimination of COD and TP mainly concentrated in the front of the wetland. The changes of COD and TP concentration were relative sable in the end of the wetland. When HRT is changed, the variation of COD and TP removal is mainly concentrated in the front of the wetland. The concentration of NH4+-N and TN gradually decreased along the plant wetlands. Thanks to the change of internal structure of the wetland, the influent contacted with the plant roots fully and efficiently and thus kept a higher pollutant removal compared with general wetland. The removal of various pollutants mainly concentrated in the front of controlled wetland and the changes for the concentration and spatial distribution of pollutants were not obvious along the wetland.8. The experiment showed that the combination of the inlet modes at the front and at the middle of the wetland could improve the TN removal, but the impact of TP, COD and NH4+-N removal were not obvious. |
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