| Hexavalent uranium (U(VI)) has the toxicity of heavy metals and radioactive. Theenvironmental problems which was caused by uranium mining and utilization hasbecome the focus at home and abroad. Past evidence has confirmed thatSulfate-reducing bacteria (SRB) can enzymatically reduce soluble hexavalent uranium(U(VI)) to insoluble tetravalent uranium (U(IV)) under anaerobic conditions. In thispaper, the sulfate reducing bacteria granular sludge (SRBGS) was obtained bydomestication cultivation. U(Ⅵ) removal by SRBGS was investigated undermicro-aerobic condition (DO:0.6-1.0mg/L), then the removal mechanism wasanalysed with FTIR， SEM-EDX，XPS and finally the deposit morphology of U wasstudied with the sequential extraction procedure. The main results of this work are asfollow：(1) Under the condition of COD/SO42-=1，acclimatization period of12weeks,SRBGS was obtained. The microbial biomass of SRBGS had increased, andmicroflora structure of SRBGS was not destroyed.(2) The results showed that U(VI) removal by SRBGS mainly occursfollowing a2-step process: Initial adsorption(first30min) and microbial reductionprocess. Facultative anaerobes,which come from the surface of SRBGS can consumedissolved oxygen, creating conditions for U (Ⅵ) reduction. The ultimate removalrates of U(Ⅵ) reached98.89%. The concentration of COD and SO42-have apromoting effect on U (Ⅵ) reduction, but they must be less than1500mg/L.(3) The initial adsorption removal rate reached87.48%under pH5. Theremoval of U (Ⅵ) increases with sludge dosage(<0.306gVSS/L). Cu2+have ainhibition effect on activated of sludge. The initial concentration of Cu2+reached200mg/L, U (Ⅵ) final removal only reached about77%. Iron is not only able to restoreU (Ⅵ), but also can consume dissolved oxygen, then promoting SRB reduction for U(Ⅵ).(4) In the system of SRBGS-U (VI) reduction, the nitrate can reoxidation foruranium, but the air can not. With the increase of test cycle，the removal rate of U (Ⅵ)decreased，and SRBGS have signs of broken. Dynamic test showed that The besthydraulic retention time is12.5h. In order to prevent reoxidation of uranium， in the actual waste water should first deal with NO3-.（5）Pseudo secondary adsorption dynamics model (R2>0.99) showed that theinitial adsorption process was mainly affected by particle surface functional groups，biological/chemical adsorption may limit U (VI) initial removal. Dissolved oxygendo not restrict U (VI) reduction rate, pseudo secondary reduction dynamics model (R2>0.94) better fitting experimental data. Analysis of FTIR, SEM-EDS indicated thatgroups-amide group, carboxyl, hydroxyl and phosphoric acid group which came fromthe surface of SRBGS was involved in uranium deposition. And ionexchanges were happened between Na+or Mg2+and UO22+. Finally, U(Ⅵ) mainlydeposited on granular sludge in the form of residual state that has a poorbioavailability, bad migratory aptitude and less secondary pollution. |
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