| Compared with biotechnology,constructed wetland has many advantages such as low operation costs,simple operation and easy management,and it has been widely used in rural domestic sewage treatment project.However,the traditional constructed wetland is always in a state of waterflooding,and the oxygen environment of the wetland bed is poor,which directly affects the effect of water purification.In addition,the traditional constructed wetland usually choose landscape plants for planting which the economic benefit is poor.It is difficult for the popularization of constructed wetland in the rural areas with agricultural production is regarded as the main source of income.Based on this situation,in this paper,constructed wetland,a portion of biological-ecological combinative technology which is described as"anaerobic-anoxic-water dropping aeration bio-contact oxidation-constructed wetland" proposed by Southeast University,was the main focus of the study.A novel economical plant tidal flow constructed wetland was designed,the tidal flow constructed wetland system is performed following the conditions of"inflow-reaction-outflow-idle".After investigating the effect of wet-dry ratio,hydraulic load,nitrogen composition,Carbon nitrogen ratio and the nitrogen and phosphorus removal charateristics of the rural domestic sewage water by the tidal flow constructed,we got the following conclusions:(1)In summer and autumn,the removal efficiency of NH4+-N,TN and TP was different under different wet dry ratio.When the tidal flow constructed wetland is reacting for 12h and idle for 8h,the removal efficiency for NH4+-N,TN and TP of the water spinach,leeks,edible amaranth,Lactuca sativa L,rice constructed wetland are both relatively high.Reaction time of 12h and the idle time of 8h is used as the operation wet-dry ratio;When the hydraulic load of the constructed wetland increased from 0.16m3/m2·d to 0.32m3/m2·d,the removal rate of NH4+-N and TP of the five kinds of constructed wetland decreased to different extend and the reoval loads all increased.The removal rate of TN all increased at first and then decreased,and reached the maximum when the hydraulic load was 0.24 m3/m2·d.In addition,The removal rates of NH4+-N and TN were positively correlated with c(NO3-)/c(TN)in five kinds of constructed wetlands,when the c(NO3-)/c(TN)increased from 0.4 to 0.61,the removal rates of NH4+-N and TN were both improved,the tidal flow constructed wetland can adapt to the fluctuation of nitrogen composition in the combined process,it has good removal effect of the TN of the combined process effluent.(2)In winter and spring,the plastic greenhouse was built,When the tidal flow constructed wetland is reacting for 12h and idle for 12h,the removal efficiency for NH4+-N,TN and TP of the senvy,watercress,spinage,cress and wheat constructed wetland are both relatively high.Reaction time of 12h and the idle time of 12h is used as the operation wet-dry ratio.When the hydraulic load of the constructed wetland increased from 0.16m3/m2·d to 0.32m3/m2·d,it is different from the summer and autumn,the removal efficiency for NH4+-N,TN and TP of the five kinds of constructed wetlands all decreased to different extend,and the reoval loads all increased;Carbon nitrogen ratio and nitrogen composition are two important factors affecting nitrogen removal efficiency of wetlands,when the C/N increased from 2.1to 4.1,the removal efficiency of the TN of the five kinds of wetland increased from 28.95%,33.77%,26.75%,37.28%,to 42.44%,50.42%,41.18%,52.1%and 38.24%,respectively.When the c(NO3-)/c(TN)increased from 0.54 to 0.69,the removal efficiency of the NH4+-N of the five kinds of wetlands increased at first and then decreased,the removal rate of TN increased first and then tended to be gentle.(3)As for the running effects of a year.The effluent TN concentration of a bunch of tidal flow constructed wetland systems,which included water spinach,leeks,Lactuca sativa L,rice constructed wetlands in summer and autumn,as well as the Wheat,watercress,spinach,mustard and cress constructed wetlands set in a greenhouse in Winter and spring,basically reached the A standard,the effluent TP basically reached the B standard with the average HLR of 0.24 m3/m2·d and the average influent concentrations of NH4+-N,TN and TP reaching 25.6mg/L?10.7 mg/L?1.94 mg/L,respectively.The optimization of substrate gradation and the addition of gypsum can be considered to rise the removal effciency.(4)Plants have different absorption characteristics of nitrogen and phosphorus nutrients.Compared the kinetic parameters Vmax and Km of nitrogen and phosphorus of the six kinds of plants which were selected from the constructed wetland,we got that cress can well adapt to the sewage with different concentration of nitrogen and phosphorus,watercress has good adaptability to the wastewater with different concentrations of phosphorus,ammonia nitrogen and high concentration of nitrate nitrogen,Mustard is more suitable for wastewater with high nitrogen and phosphorus concentration,leek and spinach are suitable for the wastewater with lower concentration of nitrogen and phosphorus,the absorption ability of amaranth to nitrogen and phosphorus was poor,it is not suitable for the selection of economic plants in tidal flow constructed wetlands;The yield of the water spinach,leeks,edible amaranth,Lactuca sativa L,rice,senvy,watercress,spinage,cress and wheat grown in the tidal flow constructed wetland can reach 6.01?1.95?2.24?0.73?2.99?3.50?1.86?3.67?0.68 kg/m2,respectively.And the benefits of the water spinach,cress and watercress can reach around RMB 4807,9347and 2449 per 667 m2,the economic is considerable.The results of the study demonstrate that,the application of economic plant tidal flow constructed wetland in the treatment of rural domestic sewage can not only remove nitrogen and phosphorus nutrients effectively,but also can achieve a great economic benefit.Therefore,it may have potential for reaching the unification of ecological benefit and economy benefit. |
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