| At present, the groundwater nitrate pollution is one of environment problems and caused the attention of the world. The researcher through a lot of experiments and tests have shown in our lakes, groundwater, there are seriously overweight NO-3-N concentration and other issues, which may induce methemoglobinemia, but also increases the likelihood of cancer, the health of human beings a great threat. According to China's drinking water health standards(GB 5749-2006) specified in drinking water NO-3-N concentration should not exceed 10 mg / L.Common method of nitrate treatment mainly include reverse osmosis, electrodialysis and ion exchange method, but these methods are often relatively high cost, so researchers at home and abroad in recent years, gradually shifting the focus to autotrophic denitrification in research. The autotrophic denitrification has the advantage is that don't need to adding the additional organic carbon, the researchers used hydrogen, sulfur ions as electron donor, made the nitrate step by step for nitrogen. This method of groundwater pollution has made great breakthrough. Therefore, this article main research content is to iron ions as electron donor to complete the process of biological nitrate removal. The main content of test is as follows:(1) Combining bacteria morphology, physiological and biochemical tests and 16 Sr RNA sequence analysis can be concluded that the similarity of Fe-118 and Pseudomonas sp..(2) Using S2-,Mn2+?Fe2+ as different electron donor, measured A14?A16?Fe-117?Fe-118?Fe-128 denitrification characteristics of the iron autotrophic denitrification medium under the same environmental conditions, respectively. The results showed that five iron autotrophic denitrifying bacteria's nitrate removal rate was highest in the Fe2+ as the electron donor. Respectively, 92.78%, 90.63%, 95.92%, 96.84%, 88.42%. Used S2- as electron donor in nitrate removal rate were 80%, 80.86%, 82.98%, 81.52%, 79.59%, while adding Mn2+ in the medium, nitrates removal rates of five bacteria are only about 50%.(3) Studied the C/N, the concentration of Fe2+ for iron autotrophic denitrifying bacteria characteristics of denitrification. Experimental results showed that nitrate removal rates were 63.29%, 66.23%, 70.67% in CO2 as the electron donor, When the C/N ratio is greater than 1.5, the nitrate removal rates were 80% above, in which the C/N =3, A14's nitrate removal reached 93.75%, C/N = 4.5, Fe-117 and Fe-118's nitrate removal were 96.39% and 96.47%. They are the best results.(4) Discussed autotrophic denitrifying bacteria growth and reproduction of the law by growth curve. When bacteria in culture medium inoculated after 48-72 h, OD600 was significantly increased and nitrate concentration appeared sharp drop at the same time. They tend to stabilize in the 5-6 days. p H accompanied by denitrification are on the rise. Eventually nitrate removal rate of A14, Fe-117, Fe-118 are 86.13%, 88.35% and 86.13% respectively, the removal rate of Fe2+ also reached 87.24%, 88.21% and 90.82%.(5) Five bacteria in Fe2+ as the electron donor condition, nitrate removal rate were 73.33%, 72.22%, 87.5%, 88.89%, 76.47%, while Fe2+ removal was 62.07%, 66.67%, 85.71%, 89.29 %, 70.1%. The result indicated that nitrate removal rate can reach 100% of combination of Z1(compound with strains, Fe2+ and reducing iron powder).(6) Establish a biofilm reactor, examines nitrate concentration in the water, p H value and hydraulic retention time influence on nitrate removal. Test results indicated that nitrate removal rate rises with the increase of the hydraulic retention time, p H in the mildly or acidic environment can make the Fe2+ difficult to be oxidized and provide enough electron donor for denitrification. When nitrate concentration is 50mg/L, p H=6 and hydraulic retention time of 12.5h, nitrate removal rate can be stabled at more than 95%. |
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