Study On Remediation Of Petroleum Contaminated Groundwater Using Air-sparging And Bio-sparging

In petroleum exploration and development process, drilling construction,petroleum extraction, fabrication processing, transportation and storage lead topetroleum leak inordinately and consequently cause serious pollution of groundwater.Petroleum contains many highly toxic substances that are carcinogenic, teratogenicand mutagenic, leading to a great threaten to human health and ecological systemsafety. Therefore, developing the cost-efficient remediation technology of petroleumcontamination groundwater is imminent.For petroleum contamination groundwater, the remediation technologies areex-situ and in-situ remediation technology. Recently, the air-sparging andbio-sparging are widely used in remediation of contaminated groundwater, due to itsmany advantages such as in situ treatment a variety of pollutants sustainable, goodtreatment efficiency, little disturbance to environment, easy installation andconstruction and low cost. There are many successful examples on petroleumcontaminated groundwater remediation by using air-sparging and bio-sparging abroad,but rare related reports exist in the literature in China. Therefore, it's essential to carryout air-sparging and bio-sparging technology in remediation of contaminatedgroundwater.This paper supported by The National Water Pollution Control and ManagementTechnology Major Projects–Shallow Groundwater Pollution Control Subject of KeyRemediation Technology and Engineering Demonstration along the Bank ofSonghuajing River which was sub-project of The Remediation Technology of shallowgroundwater petroleum contamination along the Bank of Songhuajing River. By usingairsparging and biosparging which were economic, efficient, little disturbance ofenvironment technology as repair measures remediate petroleum contaminatedgroundwater.Based on the hydro-geological conditions of petroleum contaminated sites in Northeast of China, the lab scale experiments were setup. The groundwater ofcontamination site is Quaternary loose rock pore micro-pressure water. Thickness ofaquifer is about17m. Aquifer is brown fine sand, silty sand gradually transition togravel sand, rock particles gradually thicken from top to bottom. The groundwaterflow direction of contaminated sites is southeast to northwest, water depth is about3.4m, the average hydraulic gradient is5‰which showed the obtained observations data.The main supply source of the groundwater is lateral recharge from groundwater ofmicrowave form mound. The runoff conditions and occurrence regularity and areclosely related to topography and lithology. The main mode of excretion is lateral runoff discharge.In this study,0#diesel was selected as petroleum basement. Benzene, xylene andnaphthalene were selected as target petroleum pollutants. Gravel sand, coarse sand,medium sand and silty sand were used to simulated aquifers. The static adsorptionexperiments were investigated including pollutants of adsorption equilibrium time andadsorption characteristics in the media. The experimental results showed that thepollution adsorption equilibrium time were24h in aquifer and the adsorption ofpollutants fitted linear adsorption. The sequence of adsorption capacity of pollutantsin aquifer follows as: diesel, naphthalene, xylene and benzene. The sequence ofaquifer media adsorption capacity of pollutants follows as: medium sand, coarse sandand gravel sand. The largest adsorption capacity of pollutants was medium sand. It isdemonstrated that the smaller the particle size of sand is, the greater the adsorption ofpollutants is.A one-dimensional column was set up to study the effect of factors on theremoval rate of contaminants. The results showed that the air flow rate and mediumpermeability greatly affected AS remediation efficiency. The contaminant removalrate increased with the increment of air flow rate, but the removal rate increasedslightly when the flow rate exceeding300mL/min. The bigger the hydraulicconductivity is, the better the removal efficiency is with AS remediate contaminations.In the same operating time, pulsed air injection had advantages over continuous airinjection for medium sand with low hydraulic conductivity, while the effects of two air injection modes were similar for coarse sand and gravel sand with higher hydraulicconductivity.A two-dimensional laboratory sand tank was setup to study removal rate andradius of influence during AS operation. The results showed that increased air flowrate led to wider radius of influence. But when the air flow rate increased to a certainamount, the radius of influence was no longer increased. The tank which has side wallexist boundary effect during AS operation. The gas escapes with the side wall of thetank when the air flow rate reached maximum value influencing aeration effect. Thegas distribution is not presented axisymmetric around aeration well, existing bios flowand flow around in heterogeneous media. The shape of influence aeration area wasbasically inverter cone distribution. The radius of influence with air flow rate of0.16m3/h was greater than0.12m3/h with single aeration well. The radius of influencewere24cm,27cm,55cm in gravel sand coarse sand and medium sand with air flowrate of0.28m3/h.The migration rate of TPH and benzene were faster. Xylene hasmoderate migration rate while naphthalene was lowest. The migration rate ofpollutant was faster in horizontal than in vertical. In different media layers AS removeeffects are also different. The removal efficiency in medium sand is better than that incoarse sand and gravel sand. After15days' running, the removal efficiencies of TPH,benzene and xylene reached up to77.4%,75.6%and71.3%. The removal efficiencyof benzene is better than of xylene. A number of non-volatile organic contaminantswhich remain exist in aquifer are difficult to remove. Once the aeration is stopped, theresidual contaminants in the medium will release to the groundwater.The75percents of contaminants was removed by air-sparging. A number ofnon-volatile organic contaminants which remain exist in aquifer are difficult toremove. Once the aeration is stopped, the residual contaminants in the medium willrelease to the groundwater. Therefore, petroleum contaminated groundwater was onlyused air-sparging which not achieve the purpose of completely remove pollutants, so this paper continue to remediate petroleum contaminated groundwater by usingbio-sparging. Through the screening and domestication get pollution degradationbacteria flora.5strains were obtained after separation and purification. Two strainswere high efficiency degradation bacterium. Bacteria B had good degradation effecton benzene, xylene and naphthalene while the bacteria C has good degradation effecton TPH. Bacteria B and C respectively belongs to Pseudomonas and Achromobacter.The optimal condition of pollutants degradation is that the temperature is8-15°C, pHis6-8, DO concentration is4-7mg/L, adding nitrogen and phosphorus nutrient source.Screened bacteria flora achieved the requirements in this study, the degrading bacteriacan be used as bacteria sources of follow-up experiments.A laboratory sand tank was setup to study migration rule of bacteria ingroundwater, removal rate of contaminants and removal mechanism by usingbio-sparging technique. The results showed that the sequence of transport velocity ofbacteria follows as gravel sand, coarse sand and medium sand. The sequence ofadsorption of bacteria in the aquifer follows as medium sand, gravel sand and coarsesand. After4months' bio-sparging running, the removal efficiencies of TPH, benzeneand xylene were reached up to88.2%,86.4%and81.7%. The percentage of removalcontamination is46.24%by volatilization and36.98%by biodegradation.Naphthalene was fitted to remove by using bio-sparging not by air-sparging.Benzene, xylene and naphthalene degradation kinetic equation fit well tofirst-order kinetic equation. The degradation half-life of benzene was0.4-1.7d, ofxylene was1.5-3.6d, of naphthalene was4.4-7d. Extraction metabolites of pollutants atdifferent times and through the scan analyze the degradation pathway of benzene,xylene and naphthalene.Benzene, xylene, naphthalene degradation kinetic equation fit first-orderkinetic equation well. The degradation half-life of benzene was0.4-1.7d, of xylenewas1.5-3.6d, of naphthalene was4.4-7d. Extraction metabolites of pollutants atdifferent times and through the scan analyse the degradation pathway of benzene,xylene and naphthalene.