Study On Removal Of Petroleum Contaminants In Groundwater By Biosparging

Groundwater as an important part of water resources, owing to its advantages ofextensive distribution, good quality, stability, storage capacity and convenient for use,groundwater becomes main water supply source for people in cities and which isbeing more and more extensive development and utilization.With the rapid development of global economy, rapid growth of population andaccelerated promotion of industrialization process caused the contamination ofgroundwater resource becoming more serious. The contaminants in groundwater canbe generally classified to three types: heavy metal contaminants, organic contaminantsand radioactive contaminants. Above all, organic contaminants are the most seriousand become the main source of groundwater pollution. Therefore, the treatment oforganic contaminants in groundwater got more concern and attention fromresearchers.Biosparging (BS) is a newly developed in-situ remediation technology forgroundwater pollution in the1990s. Its advantages are remediation in-situ, simpleoperation, low cost and high efficiency, etc. The BS technology has been promotedabroad and applied in many field sites projects. The domestic researches did manystudies on BS in laboratory, but the reports on field sites remediation by BS are few.In this study, we selected benzene, xylene and naphthalene as the objects which arepetroleum volatile and semi-volatile organic contaminants of groundwater in acontaminated field site. The paper focused on the BS technology for remediation ofcontaminants and analyzed of influencing factors by laboratory simulationexperiments.Through the cultivation and domestication of indigenous microorganisms incontaminated field sites, four strains which could effectively degrade benzene, xyleneand naphthalene were isolated. Moreover, the morphological characteristics of strains,gram staining and physiological and biochemical experiments were carried out in thisstudy. The results indicated that strain A was identified as brevibacterium and gram staining positive bacteria, strain B was identified as microbacterium and gram stainingpositive bacteria, strain C was identified as plesiomonas and gram staining negativebacteria and strain D was identified as pseudomonas and gram staining negativebacteria.By doing single-factor rotation tests, this paper analyzes the effect ofenvironmental factors on the growth of strains and capable of degradation wereinvestigated and the results showed that the optimum conditions is as following: thetemperature is25℃-30℃, pHis7.0-7.5, NH4Cl and KH2PO4/K2HPO4selected asnitrogen and phosphorus source for microbes, dissolved oxygen is about5.5mg/L andthe salt concentration of1%. Under the optimum conditions, the degradation ofbenzene, xylene and naphthalene by four mixed strains and each four single strainwere investigated in this study. The results showed that the degradation rate ofbenzene, xylene and naphthalene by four mixed strains are93.80%,94.14%and73.39%, respectively, which is significantly higher than that by each four single strain.Therefore, the four mixed strains were selected as the following test strain sources.Through the soil column and sand box tests, we not only determined the rate ofmigration of microorganisms in different medium, but also investigated the actualremoval effect of benzene, xylene and naphthalene by BS technology in differentmedium and heterogeneous medium. The results showed that bio-degradation wasmainly contribution to remove low concentration contaminants, compared withvolatilization. The particle size of the sand medium has a larger impact on the removalrate of contaminants by BS technology. The smaller particle size of medium is, thelarger specific surface area is. Moreover, the more microbial biomass is, the betterdegradation effect of contaminants is, on the contrary, the degradation effect ofcontaminants is worse.