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Simulation Of Treating The Acid Mine Water In Situ By The PRB Based On Visual MODFLOW

Posted on:2016-04-20Degree:MasterType:Thesis
Country:ChinaCandidate:Q WangFull Text:PDF
GTID:2191330464971679Subject:Industry Technology and Engineering
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A wide attention has been concerned on the problem of Acid mine water pollution, which harmful to the environment for the low value of the pH,containing heavy metal ions, high concentration of sulfate and other pollutants.If not treated, discharging into the environment directly, on the one hand it will pollute the surface water, lead to death of the surface water plankton, algae, fish and other creatures, desrtoy the stability of the ecological system in the area, On the other hand, if it permeated into underground aquifers, pollutants diffusion range will be widely, the impacting on the environment will delay on a long time. Some scholars propose to use permeable reactive barrier immobilization of sulfate reducing bacteria to treat the pollution in situ. Preliminary experimental study shows, the effect of the proposed method in this study very well. But it is still need to conduct further studies on the mechanism of degradation of the permeable reactive barrier. So it established the numerical model of the permeable reactive barrier on the study, including the water movement model and the solute transport model, simulating the degradation of high concentration sulfate using the permeable reactive barrier. This research mainly experimental and simulation results are as follows:(1)This study selected a medium filling permeable reactive barrier, which is uniformly mixed with four kinds of material. These are 5mm diameter ceramsite and cob (according to 1:1 ratio), amount of sludge and sulfate reducing bacteria.From the test of the column system filling the medium, effective porosity is 0.305, the coefficient of permeability is 1.12mm/s, and longitudinal dispersivity αL=0.01m,adsorption distribution coefficient Kd=8.89×10-4L/g.(2)Constructed the permeable reactive barrier sink to treat the man-made acid mine water, which selecting the mixing materials. The sink used a peristaltic pump inlet and overflowed outlet. The hydraulic retention time was set to 24h. The inlet concentration of sulfate was set to 3000mg/L.When the fluid flowed into the filling medium, the value of pH rised to neutral rapidly, suitable for the sulfate reducing bacteria growth. As the corn cob rotten to provide carbon source for sulfate reducing bacteria in the sink, the values of the conductivity of solution remained stable in the 5500-6000us/cm. According to the values of 4,5,6 and 7 sampling points of sulfate concentration, it obtained by calculation that the a first-order reaction rate λ1 and λ2 of the sulfate reducing bacteria by the linear fitting, and λ1=0.03(1/d),λ2=0.003(1/d).(3)Using the fluent software to researching the the permeable reactive barrier sink. It can be found that fluid has vortex phenomenon when it through the porous medium material.The macroscopic average flow rate of porous medium has little difference with the actual flow rate. The boundary flow were less than the central flow due to the viscous resistance effect of the porous materials in the sink, and there were dead zone at the lower end of the overflow outlet. The velocity of the flow in the ceramic medium were fast,which can reach 3-4 times than the sinlet flow rate.(4)Through the core equation of Visual Modflow software, it obtained the water flow equation and solute transport equation of the permeable reactive barrier immobilization of sulfate reducing bacteria by modifing.Compared the area where have no PRB system to the area where have the system, the former will result the pollution area spread to a large range,and need long time to reach steady state (scope of contamination and concentration does not increase nor decrease). The latter will lead to the pollutants absorbing and biodegradating by the filled medium with the emissions of pollutants, and improve the downstream environment to achieve in-situ treatment effect。The software simulation showed the concentration attenuation trend were rapid, not spread to the surrounding geological environment.(5)Based on the analysis of sensitivity factors on the water movement equation and the solute transport equation,the method of sensitivity analysis is introduced.This paper takes four parameters as the research object.The four parameters are osmotic coefficient K,adsorption distribution coefficient Kd,the first-order reaction rate of stationary phase λ2 and the first-order reaction rate of mobile phase λ1.Sensitivity analysis of these four parameters,it can be deduced that λ1 has the least effect on the model of the permeable reactive barrier treating the acid mine water.The effect of λ2,K and Kd are more than that of λ1.And λ2 is rarely related to the other three parameters.When the other basic parameters unchanged,10% amplification of this four parameters are 63.77mg/L, 94.66mg/L and 97.09mg/L,20% amplification of this four parameters are 61.11mg/L,88.23mg/L and 90.77mg/L.Amplitude fluctuation of total sensitivity are 63.45mg/L and 60.54mg/L,when the paramenters increase of 10% to 20%.
Keywords/Search Tags:sulfate reducing bacteria, numerical simulation, Fluent, Visual Modflow, solute transport, sensitivity analysis
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