Study On Transfer Station Leachate Treatment By Different Substrates Constructed Wetland

With the development of urbanization in China,the generation and accumulation of municipal solid waste(MSW)in China are increasing day by day.Municipal solid waste transfer station is responsible for the compression and transfer of municipal solid waste,and is the key hub of municipal solid waste management in China.Due to the high proportion of food waste and high water content in domestic waste in China,a large number of harmful liquids are easily produced in the process of waste compression and transportation,which cause serious harm to the surrounding environment and even human health.Therefore,proper treatment of landfill leachate from transfer station is an important guarantee for the construction of green city.As an efficient,environment-friendly and economical wastewater treatment technology,constructed wetland technology has made some progress in the treatment of landfill leachate in recent years.Compared with landfill leachate,the leachate from transfer station has higher biodegradability and more potential for biodegradation.However,there is no research on the treatment of landfill leachate by constructed wetland.Therefore,this study will focus on evaluating the treatment effect of vertical flow constructed wetlands with different substrate types on landfill leachate,and monitoring COD,ammonia nitrogen,total nitrogen and other indicators in the inflow and outflow water of wetlands with different substrate composition.By changing the effluent flow height,hydraulic load and reflux ratio of the wetland,the operation effect of the wetland was investigated,and the economic feasibility of the application of the constructed wetland in the waste transfer station project in China was analyzed.The main results are as follows1)By comparing the effects of different effluent water levels on the treatment of landfill leachate by constructed wetland,it was found that the removal efficiency of COD and total phosphorus was basically not affected by increasing the effluent water of0 cm and 50 cm from the bottom;although the ammonia nitrogen removal rate decreased by 5.8%,the denitrification capacity of the system was significantly improved,and the total nitrogen removal rate increased by 20.36%.2)The results showed that with the increase of influent load,the treatment capacity of COD,ammonia nitrogen and total nitrogen of the three groups of wetlands showed a downward trend,with the load of 50L/m~2·d,100L/m~2·d and 150L/m~2·d The removal rates of COD,ammonia nitrogen and total nitrogen of the three groups of wetlands reached more than 90%,and the load increased to 100 L/m~2·d.the average treatment rates of COD,ammonia nitrogen,total nitrogen and total nitrogen of the three groups of wetlands decreased by 4.5%,1.6%and 2.5%compared with the load of 50L/m~2·d.When the load reached 150L/m~2·d,the average treatment rates of COD,ammonia nitrogen and total nitrogen of the three groups of wetlands decreased by 13.51%,11.66%and 10.93%compared with the load of 100L/m~2·d.When the load increased from 50L/m~2·d to 100L/m~2·d,the wetland showed a good ability to resist the impact load,and the treatment effect of the wetland was not seriously affected.When the load increased to 150L/m~2·d,the constructed wetland system showed intolerance to high pollution load,and the treatment effect decreased significantly.The constructed wetland with a load of 100L/m~2·d can not only ensure the treatment effect of the system,but also improve the utilization rate of the wetland,which can be regarded as the best operation load of the system3)Three kinds of constructed wetlands with different substrates(1:5,1:3,1:2)were tested under the loading of 150L/m~2·d.The results showed that the treatment effect of the system was the best when the reflux ratio was 1:3.When the reflux ratio was 1:3,the removal rates of COD,ammonia nitrogen and total nitrogen reached 87.94%,91.60%and 80.77%.Compared with the wetland without reflux system,the removal rates of COD,ammonia nitrogen and total nitrogen increased by 11.42%,14.94%and6.41%.When the reflux ratio is 1:3 and 1:2,the treatment effect can meet the class B discharge requirements of"water quality standard for sewage discharged into urban sewers"(GB/T 31962-2015).4)There was no significant difference between manganese mine wetland and activated carbon wetland,but they were better than mixed substrate wetland.Compared with activated carbon,the particle size of manganese ore is larger,and the possibility of blockage is smaller;and the price of manganese ore is only 1/2 of activated carbon,which has higher economic benefits.Based on the characteristics of three kinds of substrates,manganese ore is the most suitable substrate for constructed wetland.5)The constructed wetland has a good effect on the treatment of the leachate from the transfer station,and has high economic benefits.Under the scale of daily treatment capacity of 10 tons,the construction cost of constructed wetland is about 106500 yuan,and the later operation cost is about 3.15 yuan/ton.Compared with the technology of the same type of treatment effect,such as advanced oxidation and membrane separation technology,the constructed wetland has great advantages in the investment in the early stage of construction and the operation and maintenance cost in the later stage,which can be applied and popularized in engineering.