| In recent years,with the increase of factory sewage and the large-scale use of farmland chemical fertilizer,the concentration of ammonia nitrogen and organic matter in the surface water source has increased significantly.If residents drink the surface water with high ammonia nitrogen without treatment for a long time,it can lead to the canceration of human organs.It has been proved that the coagulation sedimentation filtration disinfection process in the urban waterworks has no obvious removal effect on the ammonia nitrogen.The ammonia nitrogen concentration in the drinking water still has the risk of exceeding the standard.It is found that the combined process of biofilter and ultrafiltration can effectively degrade ammonia nitrogen and organic pollutants,but when the process is used to treat micro polluted drinking water,the concentration of nitrate nitrogen and nitrite nitrogen will increase,accompanied with serious membrane fouling.In order to solve this problem,in this study,when the coupling process of biofiltration and ultrafiltration is used to treat micro polluted source water,by optimizing the combination of filter materials and preparing new filter materials,the purpose is to improve the removal effect of organic pollutants and "three nitrogen" in micro polluted drinking water and control the ultrafiltration membrane fouling.Firstly,the paper investigated the effect of conventional biofilter + ultrafiltration process and the optimization of combined filter material on treating "three nitrogen" in micro polluted drinking water and controling membrane pollution.Secondly,a new bimetallic catalyst was prepared through experiments,which can degrade "three nitrogen" pollutants efficiently.And its catalytic degradation mechanism was explored.Finally,the new catalyst was applied in the biofilter process named bimetallic catalytic biofilter(BC biofilter).It was used to treat micro polluted source water by coupling with ultrafiltration process,and its effect on membrane fouling controling was analyzed as pretreatment of the ultrafiltration process.The results show that:1.When the coagulation/conventional biological filter / ultrafiltration combined process is adopted,the removal rates of ammonia nitrogen and TOC by conventional biological filters can reach 85% and 79%,respectively.However,the effluent nitrate and nitrite concentrations were increased by 130% and 65%,accompanied by serious membrane fouling phenomenon.By comparing the three-dimensional fluorescence spectrum,infrared spectrum,and molecular weight distribution of the incoming and outgoing water,it can be known that the main pollutants that cause the ultrafiltration membrane pollution are aromatic proteins and fulvic acids and other organic substances in the water.2.In order to effectively degrade nitrate nitrogen and nitrite nitrogen produced by nitrification in biofilter,the filter material in biofilter was optimized.The results show that none of the combination of activated carbon particle diatomite filter material,activated carbon quartz sand filter material and activated carbon zeolite filter material could degrade anitrate and nitrite nitrogen significantly.However,it is found that the activated carbon particle diatomite filter material is significantly better than the other two combined filter materials in reducing the pollution of ultrafiltration membrane.3.It was found that the new bimetallic catalyst prepared by loading palladium tin metal and Fe0 on ?-Al2O3 diatomite carrier filter material can reduce nitrate nitrogen to nitrogen,and the removal efficiency could reach over 78%.The catalytic activity of the catalyst is up to 0.42 mg /(L·g·min).The catalytic reduction is in accordance with the first-order kinetic equation of L-H,and the recovery rate of regeneration can be upto 99.9%.4.It is found that the bimetallic catalyst can replace the conventional quartz sand filter material to form the bimetallic catalyst biofilter process.It can effectively improve the removal efficiency of nitrate nitrogen in the treatment of micro polluted source water.The results show that the removal rate of nitrate and nitrite nitrogen is over 60% and 90% respectively,and the effluent concentration is reduced to 0.13mg/l and 0.009mg/l respectively.5.The bimetal catalytic filter biological filter / ultrafiltration coupling process has significant treatment effect when treating highly polluted source water with high ammonia nitrogen."Trinitrogen" pollutants and organic matter in water were effectively removed,and the rate of ultrafiltration membrane fouling was effectively controlled.The research results show that the biochemical system in the filter can remove aromatic proteins,fulvic acid and other organics in the water,which effectively prevents the fouling of ultrafiltration membrane.The catalytic reduction reaction increases the electronegativity of the Zeta potential of the filter water,colloid particles and flocs are not easy to deposit on the membrane surface under the action of electrostatic repulsion.6.Micro-flocculation formed in the filter can remove colloidal particles with a particle size of 200-350 nm in water,and effectively prevent the filter pore size of the ultrafiltration membrane from being blocked.Micro-flocculation can effectively reduce the van der Waals force between the colloidal particles and the ultrafiltration membrane,and change the direction of the electric double layer force.And ensure that the floc forms a high porosity filter cake layer on the membrane surface.The synergistic effect of biodegradation,catalytic reduction and micro-flocculation in the bimetal catalyzed biofilter not only solves the "trinitrogen" problem in high ammonia nitrogen source water,but also effectively mitigating the ultrafiltration membrane fouling. |
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