| Due to the urbanization and development of social economy, nitrogen and phosphorus are excessive discharged to the environment, which not only cause the eutrophication of water, but also cause serious damage to aquatic organisms and humans by the free ammonia ionizated from ammonia nitrogen. Industrial ammonia wastewater has a large discharge, complex composition and high concentration of ammonia nitrogen. The treatment of industrial ammonia wastewater is more difficult than urban?domestic? sewage. Dealling with industrial wastewater with high ammonia nitrogen effectively and economically is always a difficult problem in the field of industrial wastewater treatment of domestic and international environmental engineering. Immobilized microorganism technology is used to fix the functional bacteria in the carrier, which resist the adverse environmental conditions, maintain the activity of the bacteria, control the appropriate sludge age, and improve the removal ability of pollutants in the sewage. In recent years, Immobilized microorganism technology is applicated to strengthen the biological denitrification technology, which has become one of the research direction in the field of ammonia nitrogen wastewater.Immobilized particles for the sequencing batch reactor?SBR? experiments were made from entrapping nitrifying sludge using polyvinyl alcohol?PVA?. The nitrification efficiency and physical and chemical characteristics of immobilized particles were obtained by changing the ammonium concentration?50400 mg/L? of simulated wastewater in the SBR. Finally, immobilized particles only, activated sludge only or the mixture of immobilized particles and activated sludge were compared about the effects of nitrification and denitrification in the treatment of ammonia nitrogen wastewater using.The major conclusions were drawn as follows:1 Cultivation and domestication of activated sludge and preparation of immobilized particles.Cultivation of activated sludge: activated sludge was obtained from sequencing batch reactor operated stably of laboratory. Activated sludge was cultivated and domesticated in batch feed by simulated wastewater?NH4+-N: 50mg/L?, until activated sludge floc was firmed and the size of that was about 4070um. Moreover, the oxygen consumption rate increased to 0.4711 mg?O2?/?g?MLSS?·min? and ammonia oxidation rate increased to 0.0616 mg N/?g?MLSS?·min?.Preparation of immobilized particles: polyvinyl alcohol?PVA? and calcium chloride saturated boric acid solution were used as immobilized material and crosslinking agent respectively. Immobilized particles were made by extrusion method. The immobilized particles had the advantages of good elasticity, high gel strength, flow well and so on.2 Nitrification efficiency of ammonia nitrogen wastewater treated by embedded particles.The experiment was conducted in batch feed by a series of 2.5 L reactors. In the experiment, the volume filling rate of embedded immobilized particles was 10% and the initial concentration of ammonia nitrogen of simulated wastewater was 50400 mg/L. Results showed that the microbial activity of immobilized particles recovered gradually, the maximum removal rate of ammonia nitrogen was achieved in the first 28, 40, 46, 58, 58 cycle, respectively and the removal rates were 100%, 100%, 81.74%, 64.62% and 48.42%, respectively. Moreover, the degradation of ammonia nitrogen was in accord with the zero order reaction kinetics, and the maximum ammonia oxidation rate?Vmax? was 271.40 mg N/?L-particles h?, and the half saturation constant K was 66.69 mg/L in the stable phase of the reaction?forty-sixth cycles?.3 Study on the physical and chemical properties of embedded particlesThe mass transfer characteristics, microstructure, specific surface, microbial populations and other physicochemical properties of embedded immobilized particles were analysed. The effective diffusion coefficient of ammonia and oxygen in the particles were determined to be 0.467×10-9 m2/s and 0.279×10-9 m2/s in the stable phase reaction under the experimental conditions. The volume of embedded particles was expanded and the structure was loose, and the specific surface area and average pore diameter were 2.3 times and 1.4 times of freshly prepared particles by SEM observation and specific surface area measurement. What's more, high throughput sequencing was carried out on the microbial species of common activated sludge and the surface and the internal parts of particles, results showed that the number of microbial species was slightly lower than that of the common activated sludge and the nitrification bacteria were preferentially grown on the surface of the particles, and the denitrification bacteria grew preferentially in the interior of the particles.4 Comparative experimental study on the treatment of ammonia nitrogen wastewater with embedded particles only, activated sludge only and the mixed system.For the simulated wastewater with the initial ammonia nitrogen concentration of 50400mg/L, the experiment was carried out separately with immobilized particles only, activated sludge only or the mixture of immobilized particles and activated sludge with the same amount of nitrification sludge in the three systems. The removal efficiency of ammonia nitrogen, COD and total nitrogen were compared and the effect of temperature on the removal efficiency of ammonia nitrogen was discussed. Results showed that the ammonia removal rate of immobilized particles only was 10%40% higher than that of activated sludge only. And when the initial ammonia concentration was higher than 200 mg/L, The removal of ammonia nitrogen was efficient and stable by the mixture of immobilized particles and activated sludge. The correlation between the addition of particles and the removal of COD was not significant. The removel rate of total nitrogen removal was 16%30% in activated sludge single system, and the total nitrogen removal rate of immobilized particles only was 5%15% higher than that of activated sludge system, and the total nitrogen removal rate of the mixed system was 5%35% higher than that of activated sludge system under different initial conditions of ammonia nitrogen in simulated wastewater.At present, Embedded immobilized microorganisms technology applicated in the treatment of high ammonia wastewater is mostly studied in the laboratory. Basic research on the nitrification efficiency and physical and chemical characteristics of embedded particles is still lacking. Immobilized particles were made from entrapping nitrifying sludge using polyvinyl alcohol?PVA? in this paper. Nitrification efficiency and physical and chemical characteristics of embedded particles were discussed under different initial conditions of ammonia nitrogen. Different reaction systems were compared to make immobilized microorganisms playing better metabolic efficiency. This research could provide theoretical support for the treatment of high ammonia nitrogen wastewater, and provided new ideas for the research and development of Immobilized microorganism denitrification reactor. |
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