Study On The Remediation Of Benzene-based Groundwater Pollution By In Situ Reaction Zone

As an important freshwater resource, groundwater is closely related to humanlife. But in recent years, impertinency exploitage and utilization of groundwater,pollutant emissions and unexpected pollution spill, brought serious pollution togroundwater. While organic-benzene, including benzene, toluene, ethylbenzene,xylene(BTEX) and nitrobenzene, are important raw materials in the oil industry,they are common groundwater pollutants as well, which in oil and its derivativestransporting, could lead to benzene organic pollution by leaks and leakage in usage,production and other sectors. Benzene-based pollutants exist a Non-aqueous PhaseLiquid (NAPL) in Underground environment.BTEX belongs to light Non-aqueousPhase Liquid (LNAPL), nitrobenzene belongs to dense Non-aqueous Phase Liquid(DNAPL), they are more toxic pollutants strong, they can cause "cancer, teratogenicand the mutation" effect.Both BTEX and nitrobenzene are highly toxic pollutants andgreat threats to human health once entered into the groundwater. Therefore, thecontrol and remediation of organic-benzene pollutants in groundwater draws a lotmore widespread attention.There are indeed various groundwater treatment techniques, including out-processing method, in-situ oxidation, air sparging, bioremediation and passivetreatment walls. These techniques have their own advantages, but there are certainshortcomings: adaptability of contaminated sites, high cost of remediation andinterference on the environment. The in-situ reaction zone remediation (IRZ) is anewly developed in-situ remediation techniques. This technique can minimizeexposure of pollutants and environmental disturbance, and in respect of its effectiveremediation, fewer investment and easy construction, this technique has a lotpromising applications.On the basis of a large number of domestic and foreign literatures, we apply theIRZ technique on the remediation of underground organic-benzene pollutants, takenthe relatively scabrous BTEX and nitrobenzene as the target pollutants. In this study,we investigated a series of experiments on BTEX contaminated groundwater to examine oxidizing-remediation effect of Fenton's reagent; various factors were alsoanalyzed to determine the best treatment conditions; we investigate the influence ofgroundwater flow, subsurface lithology and other factors on in-situ reaction zonetechnique with an actual apply in remediating underground aquifer contaminated byBTEX. In addition, we did a series of experiments to examine the reduction effect ofnitrobenzene pollution by starch-modified nano-ferrite slurry, analyzed influencingfactors and comparative analysis to determine the best treatment conditions; exploredgroundwater flow, subsurface lithology and other influential factors in remediatingnitrobenzene pollutants, and explored the in-situ microbial reaction with nitrobenzenereduction products of aniline removal efficiency; use both in-situ chemical andmicrobial reaction zone techniques to remediate nitrobenzene contamination inunderground aquifer.The subject innovation is reflected in:(1) apply in-situ reaction zone technique to the remediation of groundwaterorganic-benzene pollutants, which formed effective in-situ reaction zone by injectingactive reagent into the pollution halo through injection well. The influence of hydrogeological factors on IRZ technique was also studied, coming up with a set of specificprocess parameters for technical reference for the restoration of contaminated sites.This method minimizes the disturbance to the environment, and overcome thedeficiencies of the PRB remediation techniques on excavation of contaminated soil.(2) Use starch as nano-ferrite modification material to facture coated-shapednano-ferrite, with which, deoxidized groundwater nitrobenzene pollutants. On thebasis of a series experiments, we concluded a set of technologic parameters, furthermore, research into aquifer nitrobenzene pollution.(3) Forming in-situ oxidation reaction zone by injecting Fenton's reagent intogroundwater, oxidized BTEX pollutants, determined the effective parameter, andapplied to the remediation of BTEX contaminated aquifer.We did a series of experiments to study the removal effect of Fenton's reagentand determined the optimal experimental parameters on the processing of BTEXcontamination. The result shows that①in the reaction system, the hydrogen peroxideconcentration higher, the oxidative capacity greater, and the removal effect of BTEXcontamination better; hydrogen peroxide and BTEX molar than being the same,②westudied the oxidation effect of BTEX contaminants in the groundwater under four conditions of when hydrogen peroxide and ferrous ion molar than were1,4,8and10respectively. We found out that hydrogen peroxide and ferrous ion molar than thesmaller, i.e. more of Fe2+, removal effect of BTEX is better, but too much Fe2+couldgreatly increase precipitation amount, recede BTEX removal efficiency.③The resultshows that the average BTEX removal efficiency all can achieve90%a bove Whenthe hydrogen peroxide and two price of iron ion mole ratio to8. The pH of systemfrom initial of6~7quickly reduced to3or so, by the ORP initial-44mV rapidlyincreased to450~500mV range, strong oxidation reaction system belong to theenvironment;④Theprocess of BTEX oxidation removal conform to the secondarydynamic equation.BTEX pollutants were simulated in a horizontal cuvette, in which various hydrogeological factors influencing in-situ reaction zone oxidizing BTEX effect wereinvestigated by Fenton oxidizing reagent injected through the injection well. Resultsshow that①the injected Fenton reagent could form effective in-situ chemicaloxidation zone to degrade BTEX pollutants.②Degradation residue of BTEXpollutants in each sampling is less where closer to the injection wellhead.③In theearly stage, the removal effect of BTEX is better when groundwater velocity is high(0.33m/d) while in the latter stage, better when the velocity is lower (0.11m/d).④Injected the same amount, Fenton oxidizing reagent performs better when injectedtwice rather then once.⑤Taken subsurface lithology into account, the reacting zonemaintaining time varies due to different medium pores—shorter on the grit than on thefine sand.⑥The ORP value of the sampling ports increases after injected Fentonoxidizing reagent; pH values declines diversely. The reaction system exhibits anacidic aerobic environment.With self-made nano-ferrite slurry, copper-modified and starch-modifiednano-ferrite slurry, we deoxidized nitrobenzene in groundwater. Experiments showthat different forms of zero-valent ferrite have a huge influence on nitrobenzenedeoxidization. Starch-modified nano-ferrite(0.8%) slurry deoxidized100%nitrobenzene and has the83.33%conversion of aniline.And the process ofnitrobenzene modified iron nanoparticles grout reduction treatment correspond1dynamic equation㏑C=0.7623t+0.3469.With horizontal cuvette simulating groundwater pollution status of nitrobenzene, and through the injection of starch-modified nano-ferrite slurry injected into thegroundwater environment, we got a pretty good effective in-situ reacting zone todeoxidize nitrobenzene in groundwater. Different hydro geological factors on theformation of starch-modified nano-ferrite slurry that deoxidizing nitrobenzene wereexamined and the results show that①The rate of nitrobenzene was92.98%and36.84%conversion of aniline When aquifer medium is coarse sand, injection of starchmodification of iron nanoparticles slurry concentration(5.0g/L);②The ratenitrobenzene was42.79%and22.17%conversion of aniline, when aquifer medium iscoarse sand, groundwater flow rate (0.4m/d) larger conditions,③the reduction ofnitrobenzene rate was82.98%,26.39%conversion of aniline,the local water flow(0.1m/d), aquifer medium is coarse sand. The result show that aquifer medium iscoarse sand of modified starch, injecting slurry concentration of iron nanoparticlesmore hours, the reduction of nitrobenzene best effect of aniline conversion rate is thehighest.By adding nutrients into the simulating cuvette, in-situ microbial reaction zonewas formed and strengthened the effect of aniline natural attenuation, which provide atheoretical basis for the joint of in-situ chemical reaction with in-situ microbialreactions in remediating the nitrobenzene and products of aniline. The results showthat the nutrients-added simulating cuvette can activate the indigenousmicroorganisms and when carbon, nitrogen, phosphorus has a ratio of100:5:1, theactivated indigenous microorganisms can effectively degrade the removal of aniline tonearly100%. The mercuric chloride biological inhibitors added are to inhibitmicrobial growth.On the research of in-situ reaction technique on remediating BTEX pollutants,we found that when BTEX entered into the aquifer, they formed a pollution halo, firstconcentrated at the top, around the injection well and then gradually to downstream.The diffusion of BTEX pollutant concentration in contaminated halo is graduallytop-down decreasing.22hours after the pollution, a comprehensive pollution halo ofBTEX in the simulation slot was identified. Then we injected Fenton's reagentthrough the injection well, which formed in-situ Fenton's reagent reaction zone in theaquifer. Experiments validate the gradual decrease of BTEX concentration; pollutantE (the ethyl benzene) removal efficiency can reach100%; BTX removal efficiencycan also reach above95%. Changes of pH and DO values in each sampling revealed that when injected Fenton's reagent, dissolved oxygen values were diversely higher,from the average of2.00mg/L quickly rose to20.00mg/L or so, while pH value ofeach sampling were diversely lower compared with the original degree of7.The technique of in-situ reaction zone in remediation of groundwaternitrobenzene pollution is to form in-situ chemical reaction zone by injectingstarch-modified nano-ferrite slurry through injection well, which has pretty effect onthe remediation of nitrobenzene pollution in the aquifer, with the data of nitrobenzenedeoxidization53.72%～69.75%and aniline conversion3.25%～33.20%. Whennutrients injected into the aquifer, part of the indigenous microorganisms wereactivated and formed in-situ microbial reaction zone, which increased the degradationefficiency of nitrobenzene and affected aniline degradation. The pH and DO value inthe aquifer was both higher, and the reaction system exhibits a weak alkalineanaerobic environment.