Remediation Of Nitrobenzene Polluted Groundwater By New Oxygen-releasing Bio-permeable Reactive Barrier

Among the in-situ groundwater remediation ways at home and abroad, Bio-PermeableReactive Wall (BPRB) was very promising and used in remediation. Low dissolvedoxygen (DO) concentration in groundwater was the limited index for the remediationeffect in this technology. Compared with other ways to increase oxygen, oxygenreleasing compounds (ORCs) had the incomparable advantages, including of easywork、quick oxygen supply、low cost and convenient manage. The topic of this articlewas preparing a kind of new filling medium which could not only release oxygen butalso have biological activity. At the same time, its remediation effect on nitrobenzenepolluted groundwater was studied by dynamic and static experiments.Firstly, immobilized material was prepared with polyving akohol(PVA) asembedding material, biochar as carrier and embedded nitrobenzene(NB) degradingbacteria in this project. At the same time, its removal effect of NB, the influencefactors including pH and DO, as well as the reusing condition was studied. Then, akind of new immobilized material (oxygen-releasing biochar immobilized material)with calcium peroxide (CaO2), paraffin and tourmaline was prepared on the basis ofabove biochar immobilization material because NB could be mineralized bymicroorganism in aerobic conditions. The preferred plan was got by studying itsability of adjusting pH, releasing DO and removing NB. Lastly, laboratory simulationwas conducted to discuss its remediation effect. Conclusions were obtained accordingto above study.(1) The parameter values of the substrate inhibition equation under the optimumsimulation circumstance of NB degrading bacteria were: vmax=341.57mg·g-1·h-1、Ks=6.98mg/L、Ki=393.44mg/L. The maximum biodegradation rate of free bacteriawas260mg·g-1·h-1, while that of the biochar immobilized material was720mg·g-1·h-1.The biodegradation rate inside the material was depended mostly by the mass transferor diffusion process interior the particle. The immobilized material could removemore NB when the solution was near neutral, namely, pH=6.8. The free bacteria and immobilized material couldn’t degrade NB better in anoxic condition because NBdegrading bacteria was aerobic. However, a high removal rate of near100%after24hours was still holding when the biochar immobilized material was reused20timeslater. So it could be applied as reaction medium long time in PRB.(2) The ability of different materials from strong to weak was10%CaO2>10%CaO2+t (tourmaline)>10%CaO2+p (paraffin)>10%CaO2+p+t>2%CaO2>2%CaO2+p>2%CaO2+t>2%CaO2+p+t. While the oxygen-releasing speed was2%CaO2+t>2%CaO2+p+t>10%CaO2+p+t>2%CaO2>10%CaO2+p>10%CaO2+t>2%CaO2+p>10%CaO2.10%CaO2and10%CaO2+t were the best amongthose materials and their oxygen-releasing quantity were10.12and7.29mg/(L·gmaterial) respectively. The pH values of the solution after the reaction betweenmaterials and water were similar as the above turn. The NB degradation effect ofoxygen-releasing biochar immobilized materials was very considerable, near100%about12hours. The effect would be worse when paraffin was added.10%CaO2and10%CaO2+t were still the best.(3) The medium of four simulate columns were PVA+BC、PVA+BC+bacteria、10%CaO2+PVA+BC+bacteria、10%CaO2+tourmaline+PVA+BC+bacteria（denoted asPB、PBJ、10%CaO2、10%CaO2+t for convenient record）The removal rate of PBdecreased gradually, that of PBJ was superior to that of PB, while10%CaO2and10%CaO2+t kept a more than90%rate all the time at the inflow NB concentration of300mg/L. The addition of NB degrading bacteria and tourmaline could increase the rateobviously. DO concentration of PB was keeping among7and8.5mg/L, while that ofPBJ was3-6.5mg/L. Both pH was stable at about7and changed hardly. For10%CaO2and10%CaO2+t, DO depressed after rising at first. The peak DO concentrationwas14mg/L in the initial operation stage. With the reaction going on, both DOconcentration decreased under that of PB, even below PBJ. Both pH changes weresame as DO concentration and stable near7.0. Phosphate in the inorganic salt mediumand tourmaline had a buffer effect on the increased alkalinity.