Study On The Deep Purification Of Rural Domestic Sewage By Constructed Wetlands With Aromatic Plants

Constructed wetland technology has the characteristics of low operating cost,simple management and friendly environment.It has been widely used in the deep purification projects of rural domestic sewage,but there are still some problems in the actual operation.For instance,the low economic value of traditional large emergent plants resulted in the failure to mobilize the enthusiasm of villagers for management,and the poor resistance of some vegetables affected the yield.The unreasonable matrix configuration leads to the short operating life and other problems.Therefore,it is of great practical significance to carry out the screening of new constructed wetland plants with landscape benefits,economic benefits,and high efficiency in purification and resistance.Besides,it is of signification to research substrates with high efficiency in phosphorus removal and moderate phosphorus release.In this study,aerated concrete,volcanic rock,maifanite and gravel were used as substrates,and aromatic plants such as mint and vetiver were selected to construct three groups of aromatic plant constructed wetland system with single planting and mixed planting,so as to explore the efficacy of aromatic plant constructed wetland for deep purification of rural domestic sewage tailwater.The results are as follows:（1）There were some differences among the five aromatic plants in the nitrogen absorption characteristics of different forms,but they all showed preferential adsorption characteristics of NH₄⁺-N.Comparing I_maxand K_m,it could be seen that Vetiveria zizanioidse was suitable for the treatment of wastewater with NH₄⁺-N and NO₃^--N.Menthae Herba was suitable for a wide range concentration of NH₄⁺-N,while Perilla frutescens was applicable to treat a wide range concentration of NO₃^--N but not NH₄⁺-N.Artemisiae Argyi was more suitable for the treatment of wastewater with high NH₄⁺-N concentration.Conversely,Rosmarinus officinalis L.was more suitable for the treatment of wastewater with high NO₃^--N concentration but not NH₄⁺-N.（2）Under laboratory conditions,the saturated adsorption capacity of phosphorus for four substrates,including aerated concrete,volcanic rock,maifanite and gravel,ranged from 69.44 to 3333.33mg/kg.The adsorption capacity of aerated concrete was the largest among these four substrates,while the adsorption capacity of gravel was minimal.The isothermal desorption experiment showed that the desorption rate of volcanic rock was the highest（35.92%）,followed by maifanite（28.37%）and gravel（11.41%）,and the aerated concrete had almost no desorption of phosphorus（1.21%）.（3）When the hydraulic load is 0.183m³/m²/d,the three groups of constructed wetlands had the best pollutant removal efficiency for the tail water treatment of rural domestic sewage biological unit.In view of the problem of low TN removal rate in winter,increasing influent organic carbon source（increasing influent C/N）could significantly improve the removal rate of TN.Besides,the concentration of pollutants in the three groups of constructed wetlands decreased gradually with the increase of the flow,and the downriver pond was the main place for pollutant removal.（4）The long-term monitoring results showed that CW1 had the worst removal effect of pollutants and was most affected by temperature,while CW2 had the best treatment effect.The pollutant removal effect of CW3 was between CW1 and CW2.（5）The absorption and accumulation of nitrogen and phosphorus by plants in the three groups of constructed wetland systems ranged from 30.83 to 96.69 g/m²and 2.18to 11.47 g/m²,respectively.The descending order of nitrogen and phosphorus accumulation was as follows:CW2>CW3>CW1.The contribution rates of plant absorption to TN ranged from 5.99%to 15.25%,and the contribution rates of plant absorption to TP ranged from 3.53%to 15.23%.（6）The tested aromatic plants grew well in the constructed wetland system,with both ecological benefits and economic benefits.Rudely estimated economic benefits were as follows:the theoretical economic benefits of CW1 and CW2 were 36 yuan/m²and 119 yuan/m² respectively,and the theoretical economic benefits of CW3 could reach 108 yuan/m².