| We are now facing water resource crisis, pollution of water makes the thing worse, and affects the development of civil economy and human living. The pollution of nitrogen destroys the ecological balance, makes surface water eutrophication. It also causes the dissolved oxygen of surface water to reduce, and makes hydrobiology such as fish dead, even to cause dead lake, at the same time it harms human health.At present, there are many methods to remove nitrite and nitrate from wastewater, there are mainly physical chemistry method, chemical denitrification method and biological denitrification. The disadvantages of physical method and chemical method are that the running cost is very high and they cause second pollution easily, so it is difficult to apply these. Biological denitrification method has the advantages of economic and high efficiency. Traditional nitrogen removing theory considers that denitrification always happens in anoxic or anaerobic condition, but in the resent years , many scholars have found denitrification with the existence of oxygen in laboratory, people also find the sign of nitrogen removing in practice. Pochana found that in SBR reactor the removing rate of TN is 95%, many practical aerobic nitrification reactors are often found 30% of TN lost. These signs prove the existence of aerobic denitrification. One aerobic denitrification bacteria in this experiment is called FR1, which is got via domestication of activated sludge, filtered and saved under low temperature.The biological infection of ultraviolet radiation is that it causes the structure of DNA to change, ultraviolet radiation has double biological infection of sterilization and mutation. UV-induced mutation is a new method to mutation and filtrate bacteria, which has the characteristic of simple equipment, high mutation efficiency and easy operation. Ultraviolet radiation causes microorganism gene mutation.Nearly the ten years, immobilization bacteria technology is a hotspot in N-removing field, domestic and overseas scholars develope a technology which immobilizes nitrifying bacteria and denitrifying bacteria to realize simultaneous nitrification and denitrification in a reactor. This can save ground and investment, and avoid the redundant process that nitrite has to be deoxidized to nitrate after it is oxidized, so this can save 25% of oxygen and 40% of organic carbon.According to the different mode of embedment and carbon source supply, there are three kinds technics which are delaminating embedment, mixed embedment and carbon source circulation embedment. It is a common mode to use PVA and other compounds to embed nitrifying bacteria and denitrifying bacteria mixed in immobilization. This technic mainly uses diffuse resistance to produce grads of oxygen consistence, which can form aerobic district, anoxic district and anaerobic district, so nitrification and denitrification can happen simultanetly with the existing of oxygen.In the experiment, we use aerobic denitrifying bacteria called FR1 to be UV-induced mutated, try to find better mutants, then immobilize the mutants to deal with waste water containing nitrite and nitrate.In the first step, the physiological character of FR1 is studied, first it is gram-positive, its growth curve is made, we found that after growing 24h, FR1 develops to logarithm period, and lasts to 48h, 48h～72h is its stabilization period, after 72h it develops to contabescence period. Then the influence of temperature, pH, C/N and carbon source is researched, the result indicates that the optimum temperature for FR1 is 30℃, at the temperature of 20℃, the bacteria nearly do not grow. When pH is 7, the removing rate of nitrate is the highest. With the increase of C/N, the consistence of nitrate is reduce, because when C/N is higher, carbon source is enough, the denitrification reaction completes better. When the carbon source is succinic acid, the bacteria grow better, the removing rate of nitrate is higher and nitrite does not accumulate clearly.In the second step, FR1 is mutated by UV. In the first mutation, a bacteria is filtrated called ZR43, then ZR43 is mutated once more, through the first filtration and second filtration, a better bacteria is found which is called SZR8. Then the physiological character of these two bacteria is studied detailedly. The growth curve of these two bacteria is made, the result indicates that SZR8 grows faster and develops to logarithm period when it is not 24h, after 72h, it develops to contabescence period, ZR43 grows slower, after 72h it is still growing, when it is 124h, it is still growing. Then the influence of temperature, pH, C/N, carbon source and nitrogen source is researched, the result indicates that these two bacteria have wide temperature range, but the optimum temperature for ZR43 is 35℃and for SZR8 is 30℃. In comparing with FR1, these two bacteria have wider pH range, and the optimum pH is 7 for them. The optimum C/N for these two bacteria is 8, with the increase of C/N, the removing rate of nitrate is higher, we have to choice the optimum C/N to save resource. With different carbon source, these two bacteria grow differently; sodium acetate is not perfect carbon source for these two bacteria. The adaptive carbon source scope for these is different; SZR8 has wider carbon source scope than ZR43.In the third step, the two mutants were immobilized mixed. First, a better carrier has to be chosen, there are two methods which are sodium alginate +activated carbon and PVA +sodium alginate+additive. Using the method of sodium alginate +activated carbon, the removing rate of nitrate is higher, the effect is the most obvious. So we choose sodium alginate +activated carbon for immobilization,Then the immobilized globules were put to fluid bed reactor, the influence of temperature, pH, C/N, hydraulic retention time to aerobic denitrification was researched, the result indicates that the adaptive temperament range is wide, the optimum temperament for nitrogen removing is 30℃, the optimum C/N is 4, and the optimum hydraulic retention time is 5h.
|
PDF Full Text Request