Study On The Selection And Effect Of Sewage Sludge Used As Ecological Restoration Matrix In Mine Wasteland

With the development of urbanization,municipal sewage treatment plants produce a large amount of sewage sludge,which is not properly disposed because of its harmfulness.Sewage sludge is rich in nutrients which plants need and it is a good organic fertilizer and soil conditioner,so that it can be used as good matrix for ecological restoration of abandoned lands of mines after disposed.At the same time,sewage sludge can be disposed properly,it is treated to achieve the sustainable utilization of the goal,which has good environment,ecological,social,and economic aspects of comprehensive benefit.China is a country with large mineral resources.The unreasonable exploitation of mines in the early stage has polluted the atmosphere,water and soil environment to different degrees,and can eventually endanger human health through the food chain.How to use mine ecological restoration after harmless treatment of sewage sludge is an urgent topic.Therefore,this paper firstly analyzes the coal gangue produced by an open-pit mining coal mine in Xingren city,Guizhou province,and studies its possible environmental hazards.Secondly,fly ash,lime and soil were used to improve the sewage sludge,and the improved sewage sludge was used as the ecological restoration matrix.The excellent matrix was screened through indoor pot simulation experiment.Eventually,by studying on the leachate,matrix and perennial ryegrass,physical and chemical properties analysis,to explore the effect of improved after the sewage sludge is used to mine ecological restoration.At the same time,makes the sewage sludge disposed properly,to achieve the goal of sustainable resource utilization with waste management.The main results of the study are as follows:(1)Coal gangue contains lots of pyrite,and its p H ranges from 2.09 to 4.99.The average Fe in coal gangue is 25.75g/kg,which results the mine pit water in the mining area is reddish brown and its p H is low.The average contents of As and Cd in coal gangue are 97.24mg/kg and 0.52mg/kg respectively,both of which are higher than the screened value of soil pollution risk of agricultural land.Although the content of organic matter in coal gangue is up to 21.4%?28.7%,plants cannot grow in the mining area due to its poor physical structure and large amount of heavy metal elements.(2)Heavy metal elements in the fly ash and lime can effective passivation sewage sludge,make it not easy leached out and passivation effect which mix lime with sewage sludge is better than that mix with fly ash,sewage sludge can rapidly improve the soil nutrient content,and the amount of the sewage sludge can contribute to the germination and growth of perennial ryegrass,but lots of sewage sludge is not conducive to the growth of plants.When sewage sludge,fly ash and soil were mixed in different proportions,the average germination rate of ryegrass was the highest,the average germination rate was more than 80%,and the growth rate was the best.Sewage sludge: fly ash =1:1,sewage sludge: fly ash =2:1,sewage sludge: fly ash: soil =1:1:1,sewage sludge: fly ash: soil =1:1:2,four matrixes were selected for the experiments of ecological restoration.(3)The selected matrix was used to cover the upper layer of coal gangue for the experiment of ecological restoration.The results show that when the matrix was sewage sludge: fly ash = 1:1 and sewage sludge: fly ash = 2:1,leachate p H increased significantly,EC was reduced,heavy metal elements such as Fe,Mn,Cu,Pb,Zn,Cd,Ni,As,Cd were reduced significantly.There was no migration of heavy metal elements in coal gangue into matrix.The heavy metal enrichment rate of ryegrass was not high.And when the covering matrix is urban sludge: fly ash = 2:1,the repairing effect is the best.To sum up,matrix is sewage sludge: fly ash = 2:1 which was used to covered on top of coal gangue to repair coal gangue show that: it could effectively avoid the acid mine drainage(AMD),and heavy metal elements in coal gangue and matrix has no migration phenomenon.They can be used as good matrixes for ecological restoration of abandoned lands of mines,and make plants growing in mines,which will not cause secondary pollution.