Study On Remediation And Response Mechanism Of Alfalfa On Landfill Leachate Contaminated Soil

In recent years,the total production of waste is increasing year by year,and the sanitary landfill is still the main treatment at present.Due to the multiple factors combination of water contained waste,microbial metabolism,surface runoff and so on,the waste will produce high concentration and complicated leachate in the landfill unavoidably.If the landfill management mechanism or anti-seepage system were deficient or incomplete,the leachate would be soaked into the nearby soil layer,and posed a great threat to the surrounding environmental system and human health.As the landfill leachate contaminated soil,a laboratory pot experiment was carried out to investigate the remediation effect of landfill leachate contaminated soil by using alfalfa(Medicago sativa L.),control groups were set with no planting.Measured soil leachate pH,conductivity,COD,ammonia nitrogen and air-dried soil invertase,urease,catalase activity,total nitrogen and total phosphorus regularly to examine the remediation effect in the different landfill leachate concentration contaminated soil(0ml/kg,40ml/kg,80ml/kg,120ml/kg).Thus,the alfalfa photosynthesis rate(P_n),the maximal photochemical efficiency(Fv/Fm)and the content of plant component(C,N and S)were monitored to reflect the dynamic changing trends of alfalfa tolerance and response mechanism under the condition of different pollution.Finally,the relationships between the indexes were explored through mechanism analysis.The main results were acquired as follows:(1)Through the study of soil leaching,the landfill leachate contaminated soil pH increased in some extent with the planting of alfalfa,and stabilized in the later period,it showed the acid and alkalinity buffering capacity of soil environment was improved effectively.Alfalfa also present a good salinity tolerance,it can survive in the soil with high salt concentration,and has the function of reducing soil conductivity,but the high salt content can also inhibit its growth.The ammonia nitrogen and COD removal rate of tested soil could up to 88.9%and 78.1%under the alfalfa planting,respectively.And different soil remediation effect present in different processing conditions,the ammonia nitrogen pollution remediation effect is obvious relatively.(2)Under the different conditions,we found the activity of sucrase,catalase and urease in soils were promoted to varying degrees in the experimental group,the soil sucrase activity order were listed as 80ml/kg>120ml/kg>40ml/kg>0ml/kg,the catalase activity order was 80ml/kg>40ml/kg>0ml/kg>120ml/kg,and urease order was 120ml/kg>80ml/kg>40ml/kg>0ml/kg,the activity of sucrase was the most significant,while urease activity was smaller relatively.The soil total nitrogen content in the experimental group was significantly reduced when compared with the control group,and the highest removal rate was up to 85.08%,but the total phosphorus reduction rate was relatively smaller.(3)Under different leachate treatment conditions,the moderate concentration of leachate played a key role in increasing net photosynthetic rate and the maximal photochemical efficiency of alfalfa,but the high concentration of leachate had a serious inhibitory effect on the growth of alfalfa,and this inhibitory effect will be weaken with the incubation.The plant carbon,nitrogen and sulfur content present a different degree of change under the conditions of different leachate concentration,the plant nitrogen content increased 23.9%in 120 ml/kg leachate concentration cultivation conditions when compared with no landfill leachate experimental group.The results showed that alfalfa had a good tolerance and remediation effect on high nitrogen content of contaminated soil.(4)According to the correlation analysis,the soil leachate pH present the different degree of correlation between sucrase,urease and catalase activity,the value of correlation coefficient was 0.515,0.607,0.533,respectively.The soil physical and chemical properties,soil nutrient,the spatial structure of soil enzymes all are affected by the change of pH directly.In the experimental groups,the soil nitrogen content was mainly from leachate,and the correlation coefficient of ammonia nitrogen and total nitrogen in soil was 0.72,which was significantly correlated.Due to the self-regulation ability of alfalfa,and the nitrogen content in the soil was balanced,so the correlation bentween ammonia nitrogen,total nitrogen and plant nitrogen content was not obvious.