Study On Nitrogen And Phosphorus Removal Characteristics Of Constructed Wetlands With Economic Flowers Treating Rural Wastewater

The constructed wetland is favored in domestic and foreign rural sewage treatment projects because of its low investment and operation cost and simple management in achieving the function of nitrogen and phosphorus removal.In traditional constructed wetlands,large-scale aquatic plants,such as reeds,calamus,and cattails,are effctive in removal,but their economic value and ornamental value are limited.Vegetable-type constructed wetlands can bring economic benefits but have food safety problems.Research and selection of wetland plants with ecological,landscape,and economic benefits have important implications in ecological engineering.Scindapsus aureus,Spathippyllium floribundum and other economical flowers were selected to construct a combination system of plant filter bed-underflow wetland to explore the adaptability of economical flowers to the aquatic environment and their ability to absorb nitrogen and phosphorus in domestic sewage.Conclusions are as follows:(1)The absorption kinetics of nitrogen in eight economical flowers,such as Scindapsus aureus and Spathippyllium floribundum,showed that there were significant differences in the dynamic characteristics of nitrate nitrogen and ammonia nitrogen absorption among different flowers:four kinds of flowers:Scindapsus aureus,Spathippyllium floribundum,Bambusa multiplex and Pachira macrocarpa have greater affinity or absorption rate of nitrate and ammonia nitrogen and are selected as pilot plants;while Monascus,Gardenia,Anthurium and Chrysanthemum are not recommended as wetland plants because of their low affinity or absorption rate.The static adsorption experiment of nitrogen and phosphorus by matrix showed that large gravel,small gravel,and ceramsite had a certain adsorption effect on nitrogen and phosphorus.The adsorption of nitrogen and phosphorus by ceramsite was the highest,followed by the combination of large gravel,small gravel and ceramsite.Configuration;Considering the economy of the gravel and the characteristics suitable for plant growth,the combination configuration was selected as the wetland filler for the pilot experiment.(2)This study investigated the effect of six combinations on the removal of nitrogen and phosphorus as a function of seasons.Under conditions of hydraulic loading of 0.133 m~3/(m~2·d),the removal rate of ammonia nitrogen in the combined system ranged from 32.23%to 60.81%,and the effluent reached the standard level B in June and December.Scindapsus-Bambusa,Scindapsus–Scindapsus,Scindapsus–Spathippyllium and Spathippyllium-Bambusa reaches the standard level A in July-September.The removal rate of TN was between 16.8%and 49.17%.The concentration of effluent was between 10.76 mg/L and 19.85 mg/L.The effluent in summer and autumn all reached standard A,and the effluent water quality in winter and spring reached standard B.The effluent concentration of TP was mainly affected by the concentration of influent water.From June to October,the average removal rate of TP was 68.99%,and the effluent reached standard B.Among them,Scindapsus-Bambusa,Scindapsus-Scindapsu reached the standard A in July and September.From November to March,the average removal rate of TP was 49.86%.Compared to the removal of nitrogen,the effects of plants and microorganisms are limited.(3)The effect of hydraulic loading on the removal efficiency of N and P is significant.From 0.4 to0.08 m~3/(m~2·d),the removal rate of N and P in the combined system is obviously improved,the recommended hydraulic load is 0.133 m~3/(m~2·d).In general,the removal rates of ammonia nitrogen,TN,and TP increase as the water depth increases.The inter-species differences in plants showed more pronounced removal rates of ammonia nitrogen and TN,while the TP removal rates did not differ significantly between species.The optimal depth of water in the wetlands of the Scindapsus and Bambus is 0.45m but for Spathippyllium and Pachira is 0.4m.Ammonia nitrogen,TN and TP all decreased along the course.In the filter bed,the max removal of ammonia nitrogen and TN occurred at the front end,and the TP was uniformly reduced.In the wetland,the removal rate of ammonia nitrogen and TP was highest at 1/3,and the removal rate of TN drops obviously at the rear 1/3.In the vertical direction,the concentration of ammonia nitrogen and TP are clearly stratified;however,the difference in TN concentration is not significant in the vertical direction.(4)The four plants grew well in filter beds and wetlands in summer and autumn,and they were very ornamental.However,the growth conditions in winter and spring were poor.The plant biomass arerelatedtowaterpurificationeffects.Thecomparisonresultis:Bambusa>Scindapsus>Pachira>Spathippyllium.The contribution rate of TN removal by the combined systems ranged from 8.9%to 20.8%.The highest contribution to the removal rate was the Scindapsus–Scindapsu.The contribution rate of TP removal ranged from 14.2%to 31.5%,and the highest contribution to the removal rate was the Scindapsus-Bambusa.Take the example of planting Scindapsus in summer and autumn,planting Spathippyllium in winter and spring,and roughly estimate the economic benefits.Excluding wetland infrastructure and maintenance costs and plant seedling costs,the yield per mu was 48,333 yuan.The economical flowers have a good adaptability to the aquatic environment and good absorption of N and P in domestic sewage,which can be used as a selection of artificial wetlands,bringing considerable landscape and economic value to the sewage treatment.The selected plants have poor cold tolerance,which can enhance the effect of the ecological system in winter,or select cold-tolerant varieties.