The Experimental Research And Fluorescence Spectroscopy Analysis On Biological Nitrogen Removal Process

The TN(total nitrogen) concentration of the effluents is relatively high in the wastewater treatment plants which use traditional biological denitrification technology. And it can not meet the increasingly discharge standard of the pollutant, so it is important to reform old sewage plant in order to meet the discharge standard of the effluent. The commonly used transformation methods include carbon source dosing and step-feed process.Two SBR(sequenced batch reactor) devices were operated to study the simulated wastewater treatment. After the startup of the reactor, the research on carbon source dosing and step-feed process was carried out. The pre- and post-independent denitrification stage were settled to study effect of the external carbon source and C/N(the ratios of carbon versus nitrogen) on biological nitrogen removal process. The SBR reactor was reformed with step-feed process, and comparison of nitrogen removal with different segment ratios and influent C/N was researched under the 2 segment model. With the oxidation ditch pilot device settled in the sewage treatment plant, the actual domestic wastewater was treated to study the startup and the carbon source type in enhancing the nitrogen removal process. In the process of the experiment the fluorescence spectral analysis technology was also used. The main results were as following:1. After SBR reactor aeration stage, the increasement of post anoxic denitrification phase can significantly improve the total nitrogen removal rate. The utilization efficiency of the denitrifying bacteria in the carbon source is low, adding external carbon source in the beginning of the anoxic phase to supplement the requirement of the denitrification, the denitrification effect could be enhanced. Adding equal concentrations of sucrose, sodium acetate and complex carbon source as external carbon source, the total nitrogen removal rate were 55.7%, 94.6% and 96.6%, respectively. With sodium acetate as the carbon source for denitrification, when the dosage of sodium acetate was to make the influent COD/N value reached more than 5:1, the nitrogen removal effect was the best. In the pre denitrification process, the SBR reactor can only degrade nitrate nitrogen in the remaining supernatant of previous cycle, the organic matter in raw water used for denitrification was of low proportion, and the actual removal effect for nitrogen pollutants in the influent of this cycle is not obvious.2. When the inlet section number of the SFSBR reactor was 2, the nitrogen concentration of nitrate in water was 22.7mg/L as the proportion of step-feed was 5:5, which was less than the ratio of influent water was 7:3. The results of the relationship between influent COD/N value and nitrogen removal effect showed that higher influent COD/N value could provide more carbon source for denitrification stage, and the nitrate nitrogen removal rate could higher. When carbon nitrogen ratio of the influent was above 5:1, two segment equivalent feed SFSBR process could obtain better nitrogen removal, total nitrogen removal rate of the effluent could be increased to 78.3%. Adding additional carbon source in anoxic stage could significantly enhance the nitrogen removal effect.3. The pilot device was adopted to simulate the oxidation ditch, the alternation between anoxic and aerobic can be realized in time by the adoption of intermittent aeration mode, and the simulation of oxidation ditch process could be performed. Adding external carbon source in the anoxic phase could improve the nitrogen removal capacity of traditional oxidation ditch process, the total nitrogen removal rate could increased from 47% to more than 80%. When choose sodium acetate as carbon source, nitrogen removal rate was 86.4%. The effect of nitrogen removal could be improved by using compound carbon source as the carbon source for denitrification.4. Fluorescence spectroscopy could rapidly characterize the changes of fluorescent components in the various processing stages in water samples. Metabolic product produced by microorganisms in the degradation of organic matter and intracellular substances released from microbial decay would lead to an increasement of fluorescence intensity. The concentration of humic-like acid fluorescent material increased in biological treatment stage and decreased in precipitation stage by the analysis of fluorescence regional integration method. The three-dimensional fluorescence spectrum technology can directly reflect the concentration of organic pollutants in the influent and effluent of the wastewater. The integral value of the fluorescent substance can be calculated by fluorescence regional integration method so as to statistics the removal rate of fluorescent substances in each treatment stage. There was a good correlation between the COD value and the fluorescence of the protein in the wastewater. The ratio between the area integral value of protein-like and humic-like acid(Rp/Rf) can be used as an index to evaluate the efficiency of the organic matter treatment in the sewage plant.