| With the change in die structure, component of urban sewage have extremely changed, such as increased nitrogen content and low C/N ratio. When using traditional nitrification and denitrification technology to treat urban sewage with low C/N ratio, nitrogen in form of nitrates in outlet water exceeded emission standard seriously as a result of carbon insufficience and low denitrification efficiency. Plankton in water grows greatly; the dissolved oxygen concentration reduced; the water quality became worse and the water ecological equilibrium was destroyed. In cold area in China, most of a year is at low temperature; the ice period are in the range of 3 to 6 months; water temperature of draining is generally about 10℃. Temperature change will affect absorption characteristic of the active sludge, settling property, microorganism growth and so on, thus influences biological cleaning process. In factors above, temperature is the key factor. According to water quality condition of urban sewage in cold winter, this thesis explores and studies how enhances nitrogen elimination rate in sewage with low temperature and low C/N ratio at low price, which has become current urgent research task in China. Comparing with normal temperature sewage treatment, it is complex and particular.Since the mid-1980s, at home and abroad, many research and the reports have fully certificated the existence of aerobic denitrifying bacteria. It has been report that some aerobic denitrifying bacteria under the different environment (for example soil, drainage ditch, pond, active sludge, deposit and so on) have been isolated. But these research mainly is at the normal temperature with warm-temperature microorganism, simultaneously must provide the enough carbon source, but research of sewage with low C/N by using low temperature and aerobic denitrifying bacteria rarely have the report. The metabolic activity of warm-temperature microorganism was suppressed at the low temperature seriously, but mechanism of low-temperature microorganism enables them to have the good growth and metabolism at the low temperature. Therefore, screening low temperature and low C/N aerobic denitrifying bacteria to sewage treatment will be more effective and has the practical significance.This thesis determines best operational factors through training active sludge to satisfy the condition of organic pollutant degeneration at the low temperature and low C/N ratio; Separating aerobic denitrifying bacteria at low temperature and low C/N ratio to perfect the influence of temperature on nitrogen removal; Using the fossilization technology to enhance activeness and quantity of aerobic denitrifying bacteria in reactor and solve denitrification efficiency problem of urban sewage with low C/N ratio in the winter of North China economically.The conclusions based on the above system research above are as flowing:(1) After one month acclimation of active sludge with low C/N ratio and at low temperature, which was collected from sewage treatment plant and initial control temperature was about at 10℃and C/N ratio was 8, removal rate of COD and NH4+-N were over 95% during 40 days when the sludge density reached 3500mg/L and C/N ratio was 4. Indicator organisms of the sludge were primarily firm-infusorium and the color of sludge changed from dark black, dispersed condition to light, flocculation condition, which showed that the microorganisms of sludge were adapted to the sewage basically and active sludge acclimation ended.(2) The research on influencing factors of removal rate of sewage showed that the removal rate of COD and NH4+-N were both up to over 90%, When MLSS was from 3000 to 4000mg/L, C/N ratio were from 4 to 6, inlet-water temperature was 10℃, pH values were from 7 to 8, DO density was more than 4mg/L, time was 7h and the time of running under conditions of continuous aeration running time was 30d. During the process, nitrite concentration is no more than 1.2mg/L, the removal rate of total nitrogen were from 45% to 64%. The orthogonal experiment with four factors and three levels showed that main factors influencing sewage elimination's rate --- MLSS, pH, DO, C/N was basically consistent with single factor.(3) The dynamics research of ammonia-nitrogen degradation indicated that the degradation dynamics fitted to Monod first-level reaction kinetics equation and correlation coefficients were -0.9548~-0.9856, - 0.9433~-0.9849, - 0.9548~-0.9856, - 0.9548~-0.9856 (at significant level) under conditions of different MLSS, load rate, pH and C/N.(4)In order to enhance TN removal rate of the sewage with low C/N ratio at low temperature and put forward low-temperature strategy. 5 strains of aerobic denitrifying bacteria with strong denitrification ability, which can grow at low temperature of 10℃and C/N was 4, were chosen from trained active sludge, named as HFX000, HFX01, HFX08, HFX12, HFX13 respectively. By evaluating sole strain's 16S rDNA squence, HFX00, HFX01, HF12, HFX13 strains belong to Acinetobacter, HFX08 strain subordinates in Pseudomonas, literature in related country and abroad did not report that there has been strain with the ability to aerobic denitrifying belonging to Acinetobacter.(5) Under the pure culturing condition, the growth of strains have experienced slow-growth phase, logarithmic phase, stabilization phase. The five strains' growth curve conformed to the shape of"S"and correlation coefficient reached at extremely remarkable level. The denitrification speed of the strain is the biggest when sodium acetate as the electron acceptor, KNO3 as the most suitable nitrogen source. pH value has big influence on bacterial growth, the biggest denitrification ability of strain HFX00, HFX01, HFX08, the HFX12 was found when the pH values were between 7 and 8. The pH scope was wider for strain HFX13 and the strain grew well when pH values varied from4 to 10. But when the PH value was 4, its highest denitrification rate was 94.8%, next is the pH value of 10, 7 and 8. The aerobic denitrification ability was strong when DO was 3.5mg/L. The denitrification speed increased when the temperature was bigger than 10℃, but it decreased when temperature was over 20℃, so this strain conforms to temperature growth scope of the low-temperature bacteria.When pH values were from 7 to 8, the added ratio was 5%, the sodium acetate was the carbon source, the potassium nitrate was the nitrogen source, C/N was 4, DO was more than 3.5mg/L, the temperature was 10℃, nitrogen removal rate of 5 strains increased from 85.92% (in theory) to 91.81%, the efficiency enhanced by 6.9%.(6)The research of the carrier adsorption dynamics has determined the pickling zeolite and the acid-modified bentonite as the microorganism carrier, the adsorption amount was 93.69mg/g and 95.49mg/g respectively and the stimulated equation conformed to the second-level reaction kinetics and correlation coefficient of the four kinds of carriers was from 0.9522 to 0.9891, which was at extremely remarkable level.By union fixing between the acid-modified bentonite and the mix strain, as well as adopting orthogonal test, it was determined that the most suitable content of fixing embedding dosage of ball was PVA8%, seaweed acid sodium 1%, bentonite 3%, CaCl2 is 2%; the temperature was 15℃, time was 30h, bacterial content was 50%; choosing 15% most suitable content above of reaction volume into a reactor with the active sludge, a perfect system of aerobic denitrification and nitrogen removal was formed by using aerobic denitrification and denitrification function of fixed ball as well as digestion function of active sludge, it may not only use aerobic denitrification of strain in fixed ball fully, but also overcome outflow of strain; The elimination rate of total nitrogen of sewage may stabilize above 80% in such condition.
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