Degradation Of Ammonia Nitrogen In Urban Landscape Water By Compound Immobilized Nitrifying Bacteria

Urban landscape water provides humans with necessary water resources for survival and plays an important role in people's production and daily life.However,due to rapid urbanization,industrialization and the irrational use of water resources,the problems such as eutrophication,water atrophy,excessive levels of pollutants and other phenomena arise,which bring a huge threat to resource conservation and ecological maintenance of urban landscape water.Among the many factors that cause water pollution in urban lakes,excessive ammonia nitrogen content is one of the main reasons.Therefore,obtaining efficient,convenient and low-cost ammonia nitrogen treatment by experimental research is of great significance for restoring and protecting the water quality of landscape water.In this paper,immobilized microorganism technology was used to explore an effective method for ammonia nitrogen treatment in landscape water through carrier selection,performance testing and condition optimization.The specific research contents and conclusions are as follows:1.Exploration of preparation conditions of immobilized nitrifying bacteria pellets:Using products obtained by blending chitosan?CS?and polyvinyl alcohol?PVA?by IPN as carrier matrix,adding silica,modified attapulgite,modified kaolin and artificial zeolite as carrier modifiers respectively.The optimum preparation conditions of immobilized pellets were determined by orthogonal experiments.The composition of immobilized pellets were as follows:?1?CS/PVA-SiO₂:CS content was 2.5%,PVA content was 2.5%,silica content was 0.4%,nitrifying bacteria content was 2%;?2?CS/PVA-modified attapulgite:CS content was 2.5%,PVA content was3%,ATP content was 0.8%,nitrifying bacteria content was 2%;?3?CS/PVA-modified kaolin:CS content was 2.5%,PVA content was 2.5%,modified kaolin content was 0.6%,nitrifying bacteria content was 2%.?4?CS/PVA-artificial zeolite:CS content was 2.5%,PVA content was 2.5%,artificial zeolite content was0.8%,nitrifying bacteria content was 2%.The cross-linking agent ratio of the four pellets was 15%ethanol,1%sodium sulfate and 1%NaOH,and the cross-linking time was 4 h.2.Characterization of physicochemical properties of immobilized nitrifying bacteria pellets:The immobilized pellets prepared under optimal preparation conditions were characterized by scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The result shows that the carrier of the immobilized pellet has excellent pores and pleated structure for microbial attachment growth.Moreover,the crystallinity of each component in the blend carrier decreases,and the stability increases.The hydrogen bond is closely linked to each other,which optimizes the overall performance and has good mechanical properties and reusability.3.Application research of immobilized nitrifying bacteria pellets:The immobilized pellets can reach the highest degradation rate in the simulated landscape water when the temperature is 30?,the pH is 7,the solid-liquid ratio is 2 g/100 mL and the carbon to nitrogen ratio is 2.At the same time,this study explored the CS/PVA-SiO₂ immobilized pellet's reaction kinetics.The kinetic equation fitted the Monodequation.Thekineticcoefficient:v_max=2.965×10^-3mg·L^-1·S^-1,K_S=60.493mg·L^-1.When the ammonia nitrogen concentration is lower than 15mg/L,the error rate of the actual degradation rate of ammonia nitrogen and the kinetic model is lower.4.Evaluation of degradation performance of immobilized nitrifying bacteria pellets:This study paralleled the degradation effect with free bacteria and obtained results as follows:Each immobilized pellet has excellent ammonia nitrogen degradation performance and good resistance to the changes of initial ammonia nitrogen concentration,temperature and pH.The highest degradation rate of CS/PVA-SiO₂/modified attapulgite/modified kaolin/artificial zeolite can reach more than93%.Among them,the immobilized pellets with modified attapulgite have the best adaptability to environmental factors and better treatment performance in high-concentration ammonia nitrogen.Immobilized pellets with modified kaolin shows a better treatment effect to the medium-low concentration ammonia nitrogen.Taking the ammonia nitrogen wastewater in natural lakes as degradation object,the ammonia nitrogen content in the water treated by immobilized nitrifying bacteria is lower than the limit of ammonia nitrogen in Class II water standard of GB 3838-2002Surface Water Environmental Quality Standard,which reflects its good practical value.