Research And Application On Stabilization Of MSWI Fly Ash By Mechanochemical And Its Utilization In Preparation Of Biofilm Fillers

Incineration is currently the world’s most common method of municipal waste treatment,which can reduce about 75%of the weight and 95%of the volume of domestic waste,driven by the dual wheels of national policy support and actual demand,the scale of domestic waste incineration harmless treatment in China is rapidly increasing.However,a large amount of MSWI fly ash produced in the process of municipal waste incineration is a serious environmental hazard due to its rich content of heavy metals(such as Pb,Cd,Cr,Cu,and Zn),dioxins,soluble chlorine salts,etc.,and is classified as hazardous waste by countries around the world.Currently,fly ash is usually disposed of by landfill after stabilization,but it takes up a lot of land resources and has the potential of secondary pollution,so a safe resource technology is a way to completely solve the fly ash pollution problem.In response to the lack of research on the application of fly ash,this project has carried out the research and application of water extraction and mechanical chemical method of ball milling fly ash to achieve harmlessly,and then mixing with other solid waste sintering to prepare biofilm filler,the main research content and conclusions are as follows:(1)Experimental studies on the water extraction,ball milling,and toxic leaching of fly ash were carried out.The results show that water extraction can remove most of the chloride salts from fly ash,and the optimum water extraction conditions are:solid to liquid ratio of 1:5,and the number of water extraction times is two.The leaching concentrations of heavy metals in the ball mill ash increased to different degrees at the early stage of ball milling(0-2h);with the increase of ball milling time,the leaching concentrations of heavy metals in the fly ash gradually decreased;after 24h of ball milling,the leaching concentrations of five heavy metals in the fly ash were lower than the level of TCLP(USEPA).The heavy metals in the fly ash were effectively stabilized;at the early stage of ball milling(0-2h),the concentration of heavy metals Pb in the ball milling liquor increased more obviously;with the continuous extension of the ball milling time,the concentration of heavy metals in the ball milling liquor became smaller and smaller.From the analysis of the percentage of liquid-solid distribution in the ball milling system,with the increase of ball milling time,the percentage of heavy metal distribution in the liquid gradually decreases,and the heavy metal is gradually transferred to the solid,which fully indicates that ball milling has a good stabilization effect on the heavy metal in fly ash.(2)An experimental study was carried out on the preparation of biofilm fillers(MFA fillers)by sintering ball mill fly ash with other solid wastes(waste glass,witch hazel powder,and peanut shell powder).The pore characteristics,apparent porosity,water absorption,and flexural strength of the MFA fillers prepared at different sintering temperatures were investigated,as well as the biofilm hang-up when the MFA fillers were assembled and applied to SBBR reactors.The results show that the optimum sintering temperature of MFA filler is between 800°C and 850°C.The pore size of MFA filler is uniformly distributed,ranging from 2μm to 20μm,and the water absorption reaches a maximum of 32.15%and the apparent porosity reaches a maximum of 54.68%.The bending strength is 12.34MPa,which meets the national requirement of 12MPa.(3)An experimental study on the biofilm culture of MFA filler was carried out.The results showed that the biofilm grew well on the MFA filler,with a maturation period of about 18 days,the biofilm amount reaching up to 12.1 g/L,and the average growth rate of the biofilm reaching 672.22 mg/(L·d).The water quality index of the SBBR process equipped with MFA filler tended to be stable,and the removal rates of COD and ammonia nitrogen reached 88.65%and 69.3%respectively.(4)An experimental study on the effect of an SBBR reactor equipped with MFA filler on the removal of COD,ammonia nitrogen,and total nitrogen from wastewater under different COD loadings and different C/N ratios was carried out.The results showed that the operating efficiency of the SBBR reactor equipped with MFA filler was less influenced by the COD load and more influenced by the C/N ratio.The optimum COD load was 40g/(m~2·d)when the highest COD removal rate was 93.54%and the highest ammonia nitrogen removal rate was 98.52%.The optimum C/N interval was 3-6,where the maximum COD removal was 91.24%and the full ammonia nitrogen removal was 78.4%.Overall,the effluent discharged after treatment by the SBBR reactor can meet the Class I B standard in the Comprehensive Sewage Discharge Standard(GB18918-2002).